JP4250110B2 - Wastewater treatment method - Google Patents

Description

  The present invention relates to a sewage treatment method for reducing excess sludge by dissolving sludge in sewage using an alkaline agent.

Excess sludge is always generated when sewage is treated.
Therefore, an alkaline agent is used to mix fine bubbles with a fine bubble mixing device so that the sludge in the sewage can be dissolved, and the sludge is put into an aeration tank and decomposed by microorganisms to reduce the amount of excess sludge generated. A wastewater treatment method (Patent Document 1) is implemented.
In this method, if the amount of the alkaline solubilizer used for dissolving the sludge is large, the pH value of the sewage becomes high. For example, if a large amount of an alkaline agent having a pH value of 14 is added, the pH value of sewage will be about 12.
If the sludge is put directly into the aeration tank, the high pH value inactivates the sludge decomposing activity of microorganisms and kills useful microorganisms, reducing the ability of sludge decomposition treatment in the aeration tank. Or it may be destroyed.
For this reason, conventionally, the sewage having such a high pH value is not directly put into the aeration tank, but is once returned to the flow rate adjustment tank as shown in FIG. The sewage was mixed with sewage to dilute the pH value of the returned sewage, and the value was lowered to about 7.5 before being sent to the aeration tank.
Therefore, if inflow of new sewage cannot be expected with this method, for example, equipment installed in a store or office will not generate new sewage on non-business days such as holidays, so the operation of the sewage treatment equipment will be suspended. I had to.
JP-A-9-285207

  The present invention has been made in view of the above circumstances, and by mixing the fine bubbles with a fine bubble mixing device using an alkaline agent to make the sludge in the sewage soluble, the sludge is put into an aeration tank to be a microorganism. In sewage treatment that attempts to reduce the amount of excess sludge generated by decomposing, sewage that can stably reduce excess sludge without stopping operation even if new sewage inflow is not obtained every day It is an object to provide a processing method.

In order to solve the above problems, the sewage treatment method of the present invention performs microbial treatment in an aeration tank after the raw sewage is placed in a flow rate adjustment tank to adjust the amount of inflow.
Then, the sewage acidified by the treatment is settled and separated in a sedimentation tank, and the sedimentation sludge is transferred to a storage tank. In the storage tank, the residue contained in the sludge is removed and the inflow amount is constant. Then, an alkaline agent is added to the sludge and the pH value of the sewage in the storage tank is adjusted to 7.5 to 8.5.
Furthermore, the sludge is circulated between the storage tank and the fine bubble mixing device for a certain period of time, the fine bubbles are stirred and mixed in the sludge, the sludge is solubilized, and the sludge is sent from the fine bubble mixing device to the aeration tank. repeat.
And it is characterized by draining the cleaned supernatant liquid in a sedimentation tank.

According to a second aspect of the present invention, in the configuration of the invention described above, the method for adjusting the pH value in the storage tank collects sewage in the tank in advance as needed before introducing the alkaline agent into the storage tank. In the sample test, a mixing ratio of sewage and alkaline agent whose pH value can be adjusted to 7.5 to 8.5 is obtained.
And based on the ratio, it converts into the amount of sewage of the said storage tank, determines the injection amount of an alkaline agent, and puts the quantity of alkaline agent in the said storage tank.

Since this invention is the said structure, the pH value is set to 7.5-8 in the said storage tank for the sewage acidified by the microbial treatment in an aeration tank, maintaining the function which inputs an alkaline agent and solubilizes sludge. By adjusting to .5, even if the sewage which is circulated for a certain time between the storage tank and the fine bubble mixing device and the sludge and fine bubbles are mixed by stirring and solubilized is sent directly to the aeration tank, The sludge decomposition activity of microorganisms in the aeration tank can be maintained normally.
For this reason, even if the sewage does not flow in a new day, the sewage treatment device can be operated normally without stopping the operation of the sewage treatment device. Since it is no longer necessary to stop the operation, the management becomes easier, and the amount of excess sludge can be reliably reduced for the operation time than before.
And, if the method of adjusting the pH value in the storage tank is determined by sampling the sewage in the tank at any time and determining the input amount of the alkaline agent by the sample test, depending on the type of raw sewage and the input amount of the alkaline agent It became possible to reliably adjust the pH value, which was not constant, to 7.5 to 8.5, so that effective sludge was solubilized and at the same time, the use of an excess alkali agent could be prevented.

The best mode for carrying out the present invention will be described in detail below.
As shown in FIG. 1, the method of the present invention comprises a flow rate adjusting tank 1, an aeration tank 2, a sedimentation tank 3, a storage tank 4, and a fine bubble mixing device 5, and the storage tank 4 contains sludge contained in sludge. A processing device provided with a rotary screen device 6 is used.
Then, the raw sewage sent by the liquid feed pipe 11 is put into the flow rate adjusting tank 1 to adjust the inflow amount, and then sent to the aeration tank 2 by the aeration through the liquid feed pipe 12, where the microorganisms are treated, and the liquid feed The pipe 13 is sent to the settling tank 3 where the settling tank 3 performs the precipitation separation process.
And it sends to the storage tank 4 with the liquid sending tube 9.
An alkaline agent is introduced into the storage tank 4 to adjust the sewage in the storage tank 4 so that the pH value becomes 7.5 to 8.5.

In this pH value adjustment method, sewage in which sewage in the tank is previously collected at any time in advance and the pH value can be adjusted to 7.5 to 8.5 in the sample test before introducing the alkaline agent into the storage tank 4. To obtain a mixing ratio of the alkaline agent.
And based on the ratio, it converts into the amount of sewage of the said storage tank 4, determines the injection amount of an alkaline agent, and puts the quantity of the alkaline agent in the said storage tank 4. FIG.

Then, the sewage in the storage tank 4 is circulated for a certain period of time with the fine bubble mixing device 5 via the liquid feed pipes 7 and 8, and the fine bubbles are stirred and mixed in the sludge.
The setting of the time varies depending on the type of sludge and the capacity of the apparatus. As a guideline, if the pH value falls by about 0.5 to 1.0 from the value before stirring and mixing, it is considered that the treatment can be performed here. Since it is possible, the time required for this can be adopted.
Then, the sewage is repeatedly sent back from the fine bubble mixing device 5 to the aeration tank 2 by the return pipe 10.
When the supernatant liquid in the sedimentation tank 3 is cleaned, the sewage is discharged from the sedimentation tank 3 through the drain pipe 14.
When a large amount of sludge is precipitated in the settling tank 3, the sludge is pulled out to the outside by a drawing pipe 15 opened at the bottom of the settling tank 3.

(Experimental example 1)
In order to confirm the sewage treatment effect of the present invention, the following experiment was conducted. The sewage treatment apparatus in this experiment was an existing long-time aeration system.
The treatment capacity was 1.5 m ³ / day, and a method was adopted in which surplus return sludge was returned to the aeration tank.
Sludge was started to be introduced when MLSS was 2000 mg / L.
The amount of removed BOD and SS converted to MLSS was measured and found to be 140 g / day.
Then, an experiment for 18 days was conducted.
The amount of generated sludge during this period was 140 g / day × 18 days = 2520 g.
In the meantime, MLSS increased from 3832 g at the beginning to 5722 g on the final day in the aeration tank, and the difference increased by 1890 g.
Then, the alkaline agent is introduced into the storage tank at a ratio of 0.5 cc to 1 L of sludge and adjusted so that the pH value becomes 8.0, and the sewage in the storage tank is mixed with the fine bubble mixing device for 18 days. The sludge that was circulated for a certain period of time and sludge stirred and solubilized was returned.
Conventionally, since the alkaline agent is introduced at a ratio of about 5 cc to 1 L of sludge, the pH value is about 10 to 13. This high pH value is a factor that impedes sewage treatment in the aeration tank. However, in the present invention, it becomes a value close to neutrality, so there is no problem even if it is returned to the aeration tank as it is.
The returned amount was 200 l in 18 days and MLSS was 6300 mg / l. Therefore, the MLSS return amount is 200 l × 6300 mg = 1260 g.
During this time, the MLSS of the aeration tank was almost the same as 2500 mg / L.
Therefore, the sum of the generated sludge amount 2580 g and the returned sludge amount 1260 g is 3780 g, and the amount obtained by subtracting the increased amount 1890 g, that is, 1890 g can be reduced.
In the present invention, it was confirmed that the amount of alkali agent used can be accurately controlled, and that sludge can be reduced sufficiently even when the amount of alkali agent used is one-tenth that of conventional methods.

  The present invention mixes fine bubbles with a fine bubble mixing device using an alkali agent so that the sludge in the sewage can be dissolved, puts the sludge into an aeration tank and decomposes it with microorganisms to reduce the amount of excess sludge generated. Although it is used for the treatment of sewage, it is possible that chemicals other than alkaline agents can be effectively used for the method of reducing excess sludge stably without stopping the operation of the sewage treatment equipment. There is.

It is a schematic diagram which shows the flow of this invention. It is a schematic diagram which shows the flow by the conventional method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flow control tank 2 Aeration tank 3 Precipitation tank 4 Storage tank 5 Fine bubble mixing apparatus 6 Rotary screen apparatus 7 Liquid feed pipe 8 Liquid feed pipe 9 Liquid feed pipe 10 Return pipe 11 Liquid feed pipe 12 Liquid feed pipe 13 Liquid feed Pipe 14 Drain pipe 15 Extraction pipe

Claims (2)

  The raw sewage is put into a flow control tank and the amount of inflow is adjusted, then the microorganisms are treated in the aeration tank, and the sewage acidified by the treatment is separated into sludge by the sedimentation tank and the precipitated sludge is transferred to the storage tank When the amount of inflow reaches a certain level, the alkaline agent is added to the sludge and the pH value of the sewage in the storage tank is adjusted to 7.5 to 8.5. Furthermore, the sludge is circulated for a certain period of time between the storage tank and the fine bubble mixing device to stir and mix the fine bubbles in the sludge and solubilize the sludge. The wastewater treatment method is characterized in that the purified supernatant in the sedimentation tank is drained by repeatedly sending the water to the aeration tank. The method of adjusting the pH value in the storage tank is to collect the sewage in the tank in advance as needed before introducing the alkaline agent into the storage tank, and to adjust the pH value to 7.5 to 8.5 in the sample test. Obtaining a mixing ratio of sewage and alkaline agent that can be adjusted, converting the amount of sewage in the storage tank based on the ratio, determining the amount of alkali agent to be charged, and putting the amount of alkaline agent into the storage tank The sewage treatment method according to claim 1.

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