JP3327979B2 - Septic tank sludge treatment method and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating septic tank sludge, and more particularly to a biological treatment method and apparatus capable of biologically denitrifying and dephosphorizing septic tank sludge.

[0002]

2. Description of the Related Art Currently, a guideline for the construction guideline of human waste treatment facilities-19
The treatment target of the septic tank sludge treatment method described in the 1988 version is BOD and SS, and nitrogen and phosphorus are not excluded. Therefore, the inventors have been studying a method capable of biologically treating nitrogen and phosphorus in addition to BOD and SS. Initially, after treating the septic tank sludge and pretreating the septic tank sludge in accordance with the explanation of the urine treatment facility structure guidelines, denitrification and dephosphorization of the septic tank sludge were attempted.
/ N and BOD / P ratio decreased, and it was not possible to sufficiently perform denitrification and dephosphorization.

[0003]

Therefore, the present invention relates to
Without reducing the OD / N and BOD / P ratios, sufficiently denitrified, and to provide a device with a biological treatment method of septic tank sludge that can of doing dephosphorization process.

[0004]

In order to solve the above problems, according to the present invention, the septic tank sludge that has passed through the foreign matter removal step is supplied with an air volume of 0.01 to 0.04 m / min in the storage step.
³ / m ² (storage tank area) air stirring, mechanical stirring, water flow stirring
Internal gas circulation using gas in the gas phase during the stirring or storage process
After stirring by cyclic stirring, colloidal S in the sludge
The S-soluble BOD component is transferred to the separation water side , and solid matter in the septic tank sludge is sedimented and separated without chemical using a gravity sedimentation tank, and the sedimentation tank separated water is subjected to a biological nitrification denitrification step. Alternatively, the sludge is treated in a biological denitrification / dephosphorization step, and the activated solid sludge in the settling tank and the excess activated sludge in the nitrification / denitrification step or biological denitrification / phosphorus removal step are treated in a sludge treatment step. It is a biological treatment method for septic tank sludge. Further, in the present invention, the contaminant removal device for removing contaminants from the septic tank sludge, and the amount of air per minute for storing the sludge from which contaminants have been removed are reduced.
0.01 to 0.04 m ³ / m ² (reservoir area)
Gas in the gas phase during stirring, mechanical stirring, water stirring or the storage process
With stirring means by internal gas circulation type stirring using
Storage tank and colloidal SS BOD from the storage tank
A gravity sedimentation tank for sedimenting and separating solids without chemical injection of sludge whose components have been transferred to the separation water side, and a nitrification denitrification apparatus or a denitrification / phosphorus removal apparatus for biologically treating the separated water in the sedimentation tank And a sludge treatment apparatus for treating a solid matter in the settling tank and an excess activated sludge of a nitrification denitrification apparatus or a denitrification / phosphorus removal apparatus, which is a biological treatment apparatus for a septic tank sludge. is there.

Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a process chart showing one embodiment of the processing method of the present invention. In FIG. 1, the sludge 1 in the septic tank 1 is removed from coarse impurities 15 by the screen 2 in advance, and is stored in the storage tank 4 as the sludge 3 for removing the sludge. The separated water 6 is solid-liquid separated and flows into the first denitrification tank 9 under anaerobic conditions together with the returned sludge 7 and the circulating nitrification liquid 8. In the first denitrification tank 9, nitric acid in the circulating nitrification liquid 8 is reduced and decomposed (denitrified) into nitrogen gas by denitrifying bacteria using a BOD source as a reducing agent.

Next, the activated sludge mixture in the first denitrification tank 9 is introduced into a nitrification tank 10 under aerobic conditions, and the ammonia in the liquid is oxidized to nitric acid by nitrifying bacteria. Most of the effluent from the nitrification tank 10 is circulated to the first denitrification tank 9, and the remainder flows into the second denitrification tank 11 under anaerobic conditions to remove nitric acid in the inflow liquid, and then recycle. It flows into the solid-liquid separation step 13 via the aeration tank 12. Most of the activated sludge separated in the solid-liquid separation step 13 is returned to the first denitrification tank 9 as sludge 7.
And the remainder is discharged as surplus sludge 14. The separated water 18 in the solid-liquid separation step 13 is discharged as treated water, or further subjected to advanced treatment such as coagulation treatment and activated carbon adsorption treatment.

The excess sludge 14, the contaminants 15 and the solids 16 separated in the sedimentation tank 5 are subjected to a dehydration treatment. The storage tank 4 swallows and averages fluctuations in the inflow amount of the septic tank sludge, and stores the septic tank sludge in order to constantly send a constant amount to the treatment device even during the suspension period of the pretreatment operation on Saturday and Sunday. is there. Further, the storage tank 4 plays an important role of averaging the properties of the septic tank sludge in which the SS concentration fluctuates remarkably.
Stirring is performed to prevent the formation of scum due to the floating of the water and to make the properties of the septic tank sludge uniform throughout the tank 4.

[0008] However, if the septic tank sludge is stirred with air using a large amount of air, the BOD source necessary for denitrification disappears. This is because most of the septic tank sludge currently carried in is activated sludge which was originally subjected to aerobic treatment of domestic wastewater in the septic tank.
This causes activated sludge treatment of the BOD.
Therefore, when air agitation is adopted, 0.01 to
It must be stirred at a flow rate of about 0.04 m ³ (air) / m ² (reservoir area) and about a minute. Further, as a desirable stirring method, mechanical stirring, water flow stirring, or internal gas circulation type stirring using gas in the gas phase portion of the storage tank 4 is recommended.

The reason why the sedimentation tank 5 is necessary for the solid-liquid separation of the sludge 3 in the decontamination / purification tank is that the BOD / N value is 3 or more and the BOD / P value is required for biological denitrification and dephosphorization. 25 or more, and the solid-liquid separation by the sedimentation tank can transfer the colloidal (small) SS BOD, which is the BOD component of the sludge removal tank 3 required for denitrification, to the separation water side, and This is because most of the organic solids in the septic tank sludge can be separated by sedimentation. The coagulant injection method, which is a conventional solid-liquid separation method for the sludge in the septic tank, also separates the above-mentioned colloidal SS, so that the value of BOD / N of the separated water is reduced and the denitrification is improved. You will not be able to do it. Further, in the method of mechanically and forcibly separating solid and liquid by a centrifugal separation method or the like, the colloidal SS is separated even without chemical injection. The installation position of the sedimentation tank 5 may be between the screen 2 and the storage tank 4.

Next, another embodiment of the present invention will be described with reference to FIG. 2, which is a process drawing in which a sedimentation tank 5 is provided in a stage preceding a storage tank 4 in another embodiment. Septic tank sludge 1 is screened beforehand to remove coarse impurities 15, and is subjected to solid-liquid separation in sedimentation tank 5 without undergoing coagulation treatment with chemicals. After being stored in the storage tank 4, the separated water 6 flows into the first denitrification tank 9 under anaerobic conditions together with the return sludge 7 and the circulating nitrification liquid 8, and the same treatment as in the embodiment of FIG. 1 is performed. .

In the method of sedimentation and separation immediately after the septic tank sludge 1 is separated by the screen 2, since the operation of the screen 2 is usually performed only in the daytime, the water load applied to the sedimentation tank 5 is concentrated only in the daytime. A sedimentation tank having a larger water area than the sedimentation tank 5 of the embodiment is required. However, unlike the embodiment of FIG. 1, the sediment separation water 6 stored in the storage tank 4 can be agitated with a small amount of air or stirring energy because coarse SS having a large sedimentation speed has been removed. In this case, the BOD concentration is prevented from decreasing, and the stirring becomes easy.

Next, another embodiment of the present invention for carrying out biological dephosphorization in addition to biological denitrification will be described with reference to the process chart of FIG. Septic tank sludge 1 is removed from coarse impurities 15 in advance by screen 2, stored as sludge removal tank sludge 3 in a storage tank, and then subjected to solid-liquid separation in sedimentation tank 5. The separated water 6 flows together with the returned sludge 7 into an anaerobic tank 17 under anaerobic conditions. In the tank 17, the phosphorus is released from the activated sludge, so that the phosphorus concentration in the liquid rises. However, the BOD source in the sludge of the clarification tank is absorbed by the activated sludge, so that the BOD concentration decreases. In order for phosphorus to be released from the sludge in the same tank 17 and dephosphorization activity to be expressed in the activated sludge, the BOD source must be sufficiently present in the sludge 3 in the clarification tank, and the value of BOD / P must be not less than a certain value. Must.

The activated sludge mixture in the anaerobic tank 17 then flows together with the circulating nitrification liquid 8 into the first denitrification tank 9 under anaerobic conditions, and the nitric acid in the circulating nitrification liquid 8 is removed using a BOD source as a reducing agent. It is reductively decomposed (denitrified) into nitrogen gas by nitrifying bacteria. Next, the activated sludge mixed liquid in the first denitrification tank 9 is introduced into a nitrification tank 10 under aerobic conditions, and ammonia in the liquid is oxidized to nitric acid by nitrifying bacteria, and the amount of effluent from the nitrification tank 10 is increased. The part is circulated to the first denitrification tank 9, and the remainder flows into the second denitrification tank 11 under anaerobic conditions, and after nitric acid in the influent is removed, it is solidified via the re-aeration tank 12. Liquid separation step 13
Flows into. Most of the separated activated sludge is returned sludge 7
And returned to the first denitrification tank 9, and the remainder is discharged as surplus sludge 14. The separated water 18 in the solid-liquid separation step 13 is discharged as treated water, or further subjected to advanced treatment such as coagulation treatment and activated carbon adsorption treatment.

[0014]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples. Embodiment 1 This embodiment is an example of processing performed according to the process diagram of FIG. The operating conditions are shown below. The tank volume indicates the effective volume. Sludge removal tank sludge treatment amount: 10 m ³ / day Storage tank: 30 m ³ (4 m height) Agitated air amount: 4.8 m ³ / hour Sedimentation tank (diameter 0.8 m): 0.7 m ³

First denitrification tank: 12 m ³ Nitrification tank: 9 m ³ Second denitrification tank: ³ m ³ Re-aeration tank: omitted Solid-liquid separation step, hollow fiber MF membrane separator Membrane area: 21.6 m ² Filtration pressure: −0 0.5-3.0 mAq Returned sludge amount: 31 m ³ / day Circulating nitrification liquid amount: 315 m ³ / day Aeration tank MLSS: 11000 mg / L

The results are shown in Table 1.

[Table 1]

For comparison, after the experiment in Table 1, the stirring air volume of the sludge removal tank in the storage tank was increased from 4.8 m ³ / hour to 36 m.
³ / hour increased to 3500mg on average
The BOD concentration of the sludge in the septic tank, which was kept at 1 / liter, gradually decreased to 1200 mg / l, which was three times the TN concentration.
Liters (at this time, the sludge removal tank sludge T-
(N was 400 mg / liter), however, the NOx-N concentration in the nitrification tank increased, and NOx-N began to remain in the treated water. Therefore, methanol was injected into the first denitrification tank.

Thereafter, the BOD concentration of the sludge in the septic tank was further reduced to 200 mg / liter. At this time, methanol was added to the first denitrification tank, which was necessary to obtain the same water quality as in Table 1. The volume was 38 liters / day. Thus, without injecting methanol into the first denitrification tank,
In order to perform denitrification, BOD of sludge removal tank in storage tank
/ TN ratio must be maintained at 3 or more, and the amount of air for stirring is determined by the BOD / TN
It has been found that it is necessary to keep the ratio at a predetermined value which does not drop below 3.

Example 2 In this example, the sludge removal tank sludge 1 according to the process diagram of FIG.
This is a processing example of processing 0 m ³ / day. The processing apparatus is the same as that of Example 1 except that a sedimentation tank (diameter 1.6 m, volume 3.0 m ³ ) is interposed in the preceding stage of the storage tank, and the amount of agitated air in the storage tank is 1.2 m ³ . The conditions of the flow rate and the MLSS are almost the same as in the first embodiment.

The results are shown in Table 2.

[Table 2]

For comparison, when the cationic polymer was added at 50 mg / l to the sludge removal tank sludge of the storage tank in which the amount of air was stirred at 4.8 m ³ / hour, the BOD concentration of the sediment separation water of the sludge removal tank sludge was 500 mg. Per liter and the denitrification became poor, so methanol was added to the first denitrification tank. When 40 liters / day of methanol was added, the same nitrogen removal rate as in Table 2 could be obtained.

Example 3 In this example, a sludge removal tank sludge 1 according to the process diagram of FIG.
This is a processing example of processing 0 m ³ / day. The processing device is the first
This is the same as Example 1 except that an anaerobic tank (1.2 m ³ ) was interposed in front of the denitrification tank. The conditions of the flow rate and the MLSS are almost the same as in the first embodiment.

The results are shown in Table 3.

[Table 3]

For the purpose of comparison, after the experiment in Table 3, the stirring air volume of the sludge removal tank in the storage tank was increased from 4.8 m ³ / hour to 36 m.
³ / hour increased to 3600mg on average
The BOD concentration of the sludge from the septic tank maintained at 1 / L gradually decreased to 4.5 times the TN concentration and 1760 mg / L which was 25 times the TP concentration (the removal at this time). Residue septic tank sludge TN, TP each 390,
70 mg / liter). Thereafter, the nitrogen removal performance was not affected, but the phosphorus concentration in the treated water gradually began to increase. Thereafter, as the BOD concentration gradually decreased to 25 times or less of TP, the biological dephosphorization performance further decreased, and it became impossible to perform the biological dephosphorization.

From these results, it can be seen that even if the BOD / TN ratio of the sludge in the wastewater treatment tank in the storage tank is a value at which denitrification is sufficiently performed,
It has been found that biological dephosphorization cannot be performed when the BOD / TP ratio is 25 or less. Therefore, biological denitrification,
In order to simultaneously perform the dephosphorization, the BOD / TN ratio of the sludge removal tank in the storage tank is 3 or more, and the BOD / TP ratio is 25.
It is necessary to satisfy both of the above conditions, and the amount of air to be stirred is maintained at a predetermined amount such that the BOD / TN ratio of the stored sludge purification tank sludge is 3 or less and the BOD / TP ratio is not reduced to 25 or less. There is a need.

[0026]

According to the present invention, the following effects can be obtained. (1) Denitrification can be performed without adding methanol to the first denitrification tank. (2) Biological dephosphorization of septic tank sludge becomes possible. (3) In the pretreatment process of the septic tank sludge, the content of the colloidal SS in the solid matter 16 can be reduced, so that the amount of the dehydrating chemical used can be reduced and the water content of the dewatered cake can be reduced. (4) Since there is no need to perform an aggregation treatment for dephosphorization,
The hardly dewaterable flocculated sludge is reduced or not generated. Therefore, the sludge load on the dehydrator can be reduced (reduction of the dehydrator, reduction of the amount of injected chemicals), and the water content of the dewatered cake can be reduced.

[Brief description of the drawings]

FIG. 1 is a process chart showing one embodiment of a processing method of the present invention.

FIG. 2 is a process chart showing another embodiment of the processing method of the present invention.

FIG. 3 is a process chart showing another embodiment of the processing method of the present invention.

[Explanation of symbols]

1: septic tank sludge, 2: screen, 3: sediment removal septic tank sludge, 4: storage tank, 5: sedimentation tank, 6: separated water, 7: return sludge, 8: circulating nitrification liquid, 9: first denitrification tank, 10 : Nitrification tank,
11: second denitrification tank, 12: re-exposure tank, 13: solid-liquid separation step, 14: excess sludge, 15: contaminants, 16: solid matter, 1
7: Anaerobic tank, 18: Separated water

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Shinji Yoshida 1-6-27 Konan, Minato-ku, Tokyo Inside Ebara Infilco Co., Ltd. (56) References JP-A-57-15896 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 11/00 ZAB

Claims (2)

(57) [Claims] 1. A septic tank sludge that has passed through a contaminant removal step is subjected to a storage step in which the amount of air per minute is 0.01 to 0.04 m.
After stirring by 3 / m2 (storage tank area) air stirring, mechanical stirring, water jet stirring or internal gas circulation type stirring using gas in the gas phase part of the storage process, the colloidal S in the sludge is stirred.
The S-soluble BOD component is transferred to the separation water side, and solid matter in the septic tank sludge is sedimented and separated without chemical using a gravity sedimentation tank, and the sedimentation tank separated water is subjected to a biological nitrification denitrification step. Alternatively, the sludge is treated in a biological denitrification / dephosphorization step, and the activated solid sludge in the settling tank and the excess activated sludge in the nitrification denitrification step or the biological denitrification / phosphorus removal step are treated in a sludge treatment step. The biological treatment method of septic tank sludge. 2. A contaminant removing device for removing contaminants from a septic tank sludge, and air having a capacity of 0.01 to 0.04 m3 / m2 (storage tank area) per minute for storing the sludge from which contaminants have been removed. Stirring, mechanical stirring, water flow stirring or a storage tank having stirring means by internal gas circulation type stirring using gas in the gas phase part of the storage step, and the colloidal SS BOD component from the storage tank is separated water side. A gravity sedimentation tank for sedimenting and separating solid matter without chemical transfer of the transferred sludge, a nitrification denitrification apparatus or a denitrification / dephosphorization apparatus for biologically treating the separated water in the sedimentation tank, A sludge treatment device for treating excess activated sludge of a solid substance and a nitrification denitrification device or a denitrification / dephosphorization device.