JPS58202096A - Method for controlling concentration of dissolved oxygen - Google Patents

Abstract

PURPOSE:To hold the concentration of residual substrates in a drained liquid after being aerated in a sewage system, by adjusting an amount of air to be supplied to an airflow regulator at the inflow side of an aeration tank for performing an activated sludge process in response to a DO value in a constant airflow part at the outflow side. CONSTITUTION:Sewage having flowed through an inflow opening 2 into an aeration tank 1 is biologically treated with activated sludge by O2 in air sprayed through a sparger pipe 7 connected to a variable speed blower 5 inside tanks 1a, 1b at an airflow regulating part 4. Thereafter, the sewage under the condition that its treatment is approximately completed is let flow into a tank 1c at a constant airflow part 8 to which a relatively small amount of O2 is supplied by a sparger pipe 11 connected to a constant speed blower 9. Consequently, by satisfactorily performing the treatment at the regulating part 4, the sludge flowing into the fixed part 8 is made into a stable endogeneous-respiring state, and a DO value is held at a preset one. However, when the DO value obtd. by a detecting part 12 is low, the flow rate of air from the blower 5 is increased by a regulator 13. When the sludge flows into the fixed part 8, it is adjusted to be the endogeneous-respiring state.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the control of dissolved oxygen concentration (hereinafter referred to as Do) so that the residual substrate concentration after aeration treatment in sewage facilities can be maintained at a stable and low value.

Conventionally, when supplying oxygen to wastewater flowing into an aeration tank,
Air is sent from one blower to diffuser pipes that are branched into various parts of the processing tank where aeration is performed, and the air volume is adjusted by detecting the DO value at an appropriate position within the processing tank.

Therefore, even if the DO value is detected near the outlet, it is within the area where the air volume is being adjusted.
Although it is possible to maintain the DO value of the detection unit at the set value,
Detection is performed while biological treatment is actively progressing,
The relationship with the residual substrate concentration is weak, and the residual substrate concentration in the discharged liquid becomes higher than the expected value, making it impossible to monitor the progress of biological treatment, which is the original purpose of supplying air. However, the main purpose was to save electricity for aeration.

The present invention has been improved in view of these points, and in the embodiment shown in FIG. 9, l is an airage run tank, and in the embodiment, there are three tanks/m and /b.

/c. 2 is the inlet, 3 is the outlet to the final sedimentation tank, l occupies the majority of the tank from the inlet, and the tank/
A diffuser pipe 7, which is supplied with air from a variable speed blower S through a pulp 6, is disposed in the air volume adjustment section including a and 7b. 1 is the air volume foot section consisting of the rear half of the aeration tank/, for example, the tank/C, and is equipped with an aeration pipe// which is supplied with air from a constant speed blower via a valve/θ. /2 is the DO detector installed at an appropriate position between the air volume and the foot, /3 is the D
This is a controller that adjusts the rotation speed of the variable speed blower S or the opening degree of the valve B based on the detection output of the O detector 12.

The sewage that has flowed into the aeration tank from the inlet λ is first mixed with activated sludge by the oxygen in the air that is blown out from the aeration pipe 7 connected to the variable speed blower j in the tanks /a and /b of the air volume adjustment section. Biological treatment is carried out, and when the treatment is almost completed, the air flows into the air flow tank /C where a relatively small amount of oxygen is supplied by a diffuser pipe connected to a constant speed blower 9.

Therefore, if the treatment in the tanks 7g, /, and b of the air volume adjustment section t is performed well, the state of the sludge flowing into the air volume - foot zone /C will be in a stable endogenous respiration state. The DO value is also maintained at the set value, but if the detected DO value becomes low, this indicates that substrate decomposition accompanied by oxygen consumption is actively occurring even after the inflow. In this case, the air volume of the diffuser pipe 7 is increased via the variable speed blower j, and the amount of air supplied to the air volume adjustment part v is increased to perform effective decomposition activities, and the air flows into the air volume - leg area. Sometimes the patient is forced to adjust to a state of endogenous respiration.

Furthermore, when the detected DO value is high, the air volume to the diffuser pipe 7 is restricted so that the air supply does not become excessive.

FIG. 2 shows another embodiment in which the aeration tank l is
Consisting of two tanks /a, /b, /c, /d, the diffuser pipe /g installed in the first half tank /b is connected to variable speed blower j, and installed in the other tanks /a, /c, /d. Diffusion pipe/3. /O and /7 are each connected to a constant speed blower.

Hence the influx Roy. The sewage that has flowed into the tank/a is
Initial biological treatment is performed by air supplied from diffuser pipe /3, which flows into the air volume adjustment section of tank /b, and active treatment is performed by adjusting the air volume from variable speed blower j. Supplementary substrate decomposition is performed in tank /c, and the substance flows into tank /d in a stable state of endogenous respiration, and DO detection is performed in this state.

In this example, as a result of the experiment, the distance between the air volume adjustment section and the DO detection section is long, so the DO detection value fluctuates slightly as shown in curve A in Figure 3, but the residual substrate concentration is low, and the air volume adjustment may be the minimum air volume for stirring the tank, as shown by curve B.The total air volume can be reduced compared to the conventional case where the air volume of all tanks is adjusted.

Note that the air volume - the air volume at the feet is determined by taking into account operating conditions, seasonal water temperature, and other factors.

In this way, in the present invention, the aeration tank has an air volume adjustment part that occupies most of the inflow side and is able to adjust the volume of air blown out from the aeration pipe arranged here, and an air volume adjustment part that is provided on the discharge side and is arranged in this part. Air volume with a constant air volume from the installed air diffuser pipe - A foot section is provided, and the air volume is adjusted to the air volume adjustment section according to fluctuations in the detected value of a DO detector installed at an appropriate position of the air volume - foot part. Since the activated sludge condition in the air volume and foot section is adjusted to a stable endogenous respiration condition, the state of biological treatment in the aerated gin tank can be determined by the detected DO value, and the DO value can be determined. By keeping the concentration within the set range, the residual substrate concentration in the effluent can be maintained at a low value. In addition, since the air volume adjustment section with a high substrate concentration adjusts the air volume according to the substrate concentration, the efficiency of air usage is high and the power consumption of the aeration tank can be reduced, making it an effective measure for energy conservation.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, FIG. 2 is a schematic diagram showing another embodiment, and FIG. 3 is a characteristic curve diagram of Do detection value and air volume showing experimental results. / is aeration tank, 2 is inlet, 3 is outlet,
gu is an air volume adjustment part, j is a variable speed blower, 7 is a diffuser pipe, l is an air volume - foot part, 9 is a constant speed blower. 1/ is a diffuser pipe, /2 is a Do detection unit, /3 is a controller, and 1-/7 are diffuser pipes. Figure 1 Figure 2 Figure 3 → Time

Claims (1)

[Claims] 1. An airage run tank that performs activated sludge treatment is equipped with an air volume adjustment part that is installed on the inflow side and can adjust the supply air volume, and an air volume constant part that is installed on the discharge side and supplies a constant air volume, A method for controlling dissolved oxygen concentration, characterized in that the amount of air supplied to the air amount adjusting section is adjusted in accordance with a change in the detected value of the Do detector, so that the activated sludge in the constant air amount section is brought into a state of endogenous respiration. .