JPH02194897A - Do control apparatus - Google Patents

Abstract

PURPOSE:To control DO variations even for an abrupt change in inflow sewage amt. by estimating the aeration amt. required at a point the sewage reaches the outlet of an aeration tank when variations in the inflow amt. of sewage in the aeration tank are detected and controlling the schedule of changes in air amt. predictively. CONSTITUTION:An aeration tank 1 is provided with PI control device having a DO meter 2 as detecting means at its beginning and an aeration amt. adjusting meter 4 as operating means at its end and with an inflow amt. variation detector 13 for sensing variations in the inflow amt. of sewage in the aeration tank. There are also provided an arrival time computing arithmetic unit 14 for computing the time required until variations in the inflow sewage amt. reach the mounting point of the DO meter 2, an air amt. multiplying memory device 11 for stable DO value and a required aeration amt. estimating device 15. In addition, there are provided an aeration amt. setting device 17 for determining a change in the air amt. so as to attain an estimated required air amt. computed by the air amt. multiplication after the arrival time computed by the aforesaid arithmetic unit 14 and an integral element arithmetic unit 12 for computing the correction amt. of the air flow.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for controlling Do constant in an aeration tank in the activated sludge method, which is most widely used in sewage treatment.

[Conventional technology]

The activated sludge method uses the action of activated sludge (aerobic microorganisms) to decompose pollutants in inflowing sewage and purify the sewage. In this method, activated sludge, which is the main active ingredient, must be maintained in a good environment.

The first factor in environmental conditions is dissolved Ms in water.
degree (DO), and to ensure this, air is blown into the aeration tank.

However, if the aeration air volume becomes excessive, the activated sludge becomes finer, resulting in a decrease in purification ability and worsening of sedimentation in the final sedimentation tank, as well as a large energy loss.

In consideration of the above points, Do constant control is implemented to maintain the DO at the aeration tank outlet constant.

FIG. 3 shows a block diagram of constant DO control using a conventional PI (proportional integral) control system.

According to this control system, the required aeration air volume is determined by the DO controller 3 using the Do measurement value detected by the Do meter 2 installed at the aeration slide outlet and the preset DO value 9. Calculated. This calculation is based on the set DO value 9 and D
PI using the deviation of the O measurement value and the rate of change of the DO measurement value
Calculation methods are common.

Next, set the required aeration air volume obtained by calculation.
The air flow rate is manually input to the air flow controller 4 as the air flow rate lO. The air volume controller 4 compares the air volume measured by the air volume meter 5 and the set aeration air volume 1.
From 0, the operating amount of the solenoid valve 6 for adjusting the air volume is calculated, and an opening/closing 11 operation command is output to the solenoid valve 6.

Conventionally, the above-described steps have been used to control the DO value at the outlet of the aeration tank to be kept constant.

By the way, changes in DO in the aeration tank are caused by changes in the inflow pollution load, that is, the product of the sewage flowing into the aeration tank ↑ and the concentration of pollutants Tt in the sewage flowing into the aeration tank, and changes in the respiration rate of activated sludge.

Among these factors, factors other than the amount of sewage flowing into the aeration tank had a relatively small rate of change and could be handled by conventional control systems. However, the amount of sewage flowing into the aeration tank is determined by the operating status of the sewage pump that initially sends sewage to the settling tank, and the operation of the sewage pumps is often controlled by the number of sewage pumps.

Therefore, changes in the amount of sewage flowing into the aeration tank caused by changing the number of sewage pumps are steep and the amount of change is large. Conventional control systems have difficulty coping with such fluctuations.

[Problem to be solved by the invention]

As mentioned above, in the conventional Do constant control system, it is difficult to cope with the fluctuations in the sewage flowing into the aeration tank caused by changing the number of sewage pumps and to maintain the DO at a constant value.

That is, when increasing the number of sewage pumps, the amount of sewage flowing into the aeration tank increases rapidly, causing a decrease in DO in the aeration tank. In addition, when the number of sewage pumps decreases, the problem with conventional glue is that Do increases.

Existed in constant control systems.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a DO-constant control device that can cope with rapid fluctuations in the amount of sewage flowing into an aeration tank.

[Means to solve the problem]

In order to achieve this objective, the DO control device of the present invention uses a PLL control coloring system with a DO meter installed in the aeration tank as the detection end and an aeration air flow rate controller as the operation end, and an aeration tank inflow sewage flow meter. , aeration (inflow rate fluctuation detection device that detects changes in the amount of inflow sewage; arrival time calculation device that calculates the time for fluctuations in inflow amount to reach the installation point of the DO meter; and an air volume magnification storage device that stores an air volume magnification of , a required aeration air volume estimation device that estimates the required aeration air volume from the air volume magnification stored in the air volume magnification storage device and the amount of sewage flowing into the aeration tank, and the arrival time calculation device. An aeration air volume setting device that determines the schedule for changing the aeration atmosphere so that the estimated required air volume is calculated from the air volume multiplier after the calculated arrival time, and an aeration air flow m correction based on the deviation 1 between the measured value of DO and the set target value. The present invention is characterized by comprising an integral component calculation device for calculating ↑.

〔Example〕

Hereinafter, the present invention will be specifically described based on embodiments shown in the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. The aeration j'J l is equipped with a Do meter 2 that measures the DO value at its outlet, and from the measured value and the set DO value 9,
DO controller 3 uses PI calculation to set aeration air ff1l.
o is output. With the air volume controller 4, the set aeration air volume lO
By using PI calculation as the target value and the output from the airflow meter 5 as the measured value, an opening/closing operation command is output to the electric valve 6 so as to maintain the set aeration airflow rate of 10. As a result, blower 7
The amount of aeration air is controlled.

The air volume magnification storage device 11 calculates and stores the ratio of the amount of sewage flowing into the aeration tank to the aeration air volume when the measured value of the aeration tank inflow sewage flow meter 8 and the Do measurement value are stable, that is, the air volume magnification. . The integral component calculation device 12 calculates a correction amount for the aeration air volume t from the deviation k of the D○ measurement value and the set DO value. The inflow single fluctuation detection device 13 detects fluctuations in the flow rate of inflow sewage from the measured value of the flow rate of inflow sewage, outputs the occurrence of a fluctuation to the arrival time calculation device 14 and the required aeration air volume estimation device 15, and also outputs the occurrence of the fluctuation to the arrival time calculation device 14 and the required aeration air volume estimation device 15. The aeration air volume switching command 18 is output, and the output source of the set aeration air volume 10 is switched from the normal Do controller 3 to the aeration air volume setting device 17 system.

When a change in the flow rate of inflowing sewage is detected, the arrival time calculating device 14 calculates the time required for the currently flowing sewage to reach the outlet of the aeration tank 1 from the flow rate and the volume of the aeration tank 1. . When a change in the flow rate of inflowing sewage is detected, the required aeration landscape estimating device 15 calculates the required aeration airflow when the currently inflowing sewage reaches the aeration tank outlet, based on the flow rate and the stored air volume magnification. The position is estimated based on the following formula.

Required aeration air volume = inflow sewage flow rate
A schedule for changing the set aeration air volume is created so as to shift from the current aeration air volume to the aeration air volume estimated by the required aeration air volume estimation device 15. The aeration style setting device 17 periodically outputs the set air volume value according to the aeration air volume change schedule.

Regarding the operation of the control device of the present invention equipped with the above device,
The explanation will be divided into a normal time when the sewage flow m flowing into the aeration tank is stable, and a fluctuation time when a fluctuation in the sewage flow rate is detected.

(1) Do constant control during normal times During normal times when the flow rate of sewage flowing into the aeration tank is stable,
Do constant control is performed using a method similar to the conventional method.

That is, the Do value at the outlet of the aeration tank 1 is measured by the Do meter 2, and using this measured value and the set Do value 9, P! in the Do controller 3 is calculated. The required aeration air volume is calculated by the calculation. Next, the required aeration air volume is the set aeration air volume (4) IO
is input to the air volume controller 4 as follows. Setting aeration wind 110
As DOJ! Whether to use the output from the meter 3 or the output from the aeration air volume setting device 17 and the integral component calculation device 12 is determined by the set aeration air volume switching command that is output depending on the fluctuation of the inflow sewage flow. 18. In normal times, the output from the Do controller 3 is selected.

Next, the air volume controller 4 calculates the operation of the electric valve 6 for air volume adjustment based on the air volume measured by the air volume meter 5 and the set aeration air volume 10, and outputs an opening/closing operation command to the electric valve 6. Further, during this operation period, the ratio of the aeration air volume measured by the air flow meter 5 to the inflow volume measured by the aeration tank inflow sewage flow meter 8, that is, the air volume magnification is stored in the air volume magnification storage device 11.

In this way, during normal times when the flow rate of sewage flowing into the aeration tank is stable, the same Do constant control as in the past is implemented.

(2) Constant Do control when aeration tank inflow sewage outlet fluctuates Generally speaking, the amount of sewage flowing into a sewage treatment plant is small during late night hours and large during daytime hours. Therefore, the number of operating sewage pumps is also increased or decreased accordingly, causing fluctuations in the flow rate of sewage flowing into the aeration tank.

Detection of fluctuations in the flow rate of sewage flowing into the aeration tank is performed based on the measured value of the flow rate meter 8 of sewage flowing into the aeration tank. That is, as shown in Figure 2, the flow rate of inflowing sewage is measured every minute, and (na)
The average inflow sewage flow rate Q2 from time to current time n and the average inflow sewage flow IQ from time (n-c) to time (n-b) are determined. And the difference Δ between Ql and Q2
If the absolute value of Q is equal to or greater than the set value, it is detected that a fluctuation in the flow rate of inflowing sewage has occurred.

Here, the set value is determined based on the maximum value of flow rate fluctuation that can be handled by the constant Do control system during normal operation.

Note that the inflow sewage flow m from time (n-b) to time (na) was excluded in order to eliminate the transient part of the flow rate change due to the change in the number of units.

When a fluctuation in the flow rate of sewage flowing into the aeration tank is detected, the arrival time calculation device 14 calculates the time H for the fluctuation to reach the outlet of the aeration tank 1 based on equation (1).

H-work V-t/Q ・・・・・・・・・・・・
...(1) However, V. is the volume of the aeration tank 1, and Q is the flow rate of sewage flowing into the aeration tank after the change.

In addition, the required aeration air volume estimating device 15 calculates the required air flow ff1AQ using equation (2) using the air 1 magnification recorded in the air volume magnification storage device 11.

AQ=Kl/Q・・・・・・・・・・・・
-(2) However, is the fffffl magnification, and Q is the flow rate of sewage flowing into the aeration tank after the change.

Next, the aeration air volume schedule device 16 creates a schedule for changing the air volume so that the current aeration air volume IAQ becomes the aeration air volume AQ after H hours. An example of schedule creation is the following method.

n=H/TC・・・・・・・・・・・・(3)ΔAQ−
(ΔQ−ΔQa) / n・・・・・・・・・・・・(
4) A Q+ = A Qg + i・ΔΔQ...
(5) Here, Tc is the update cycle of the set air volume output from the aeration air volume setting device 17, and i is the number of updates.

According to this method, a schedule in which the set aeration style changes in an arithmetic manner is created.

The aeration air volume setting bag @17 updates its output value at regular intervals based on the aeration air volume change schedule.

On the other hand, the integral component calculation device 12 calculates the correction amount of the set air volume using equation (6) so that the Do value is maintained at the set value.

AQc=ni+(DOsp-Do,) ・・・・・・
...(6) Here, AQc is the corrected air volume, Do8. is a set Do value, DOl is a measured Do value, and KI is a proportional coefficient.

Then, the output AQm from the aeration air volume setting device 1f17 and the output AQc from the integral component calculation device 12 are added, and the result is manually input to the air volume controller 4 as the set aeration air volume 10.

As an output source of the set aeration airflow m10, an aeration airflow setting device 1
7 and the integral component calculation device 12 are selected by the set aeration air volume switching command 1 that is output when a change in the amount of inflowing sewage is detected.
8.

In the air volume controller 4, from the measured value and set value, the electric valve 6
The operation is performed in the same way as in normal times.

Then, after the estimated arrival time H has elapsed after the detection of the flow rate fluctuation, the control is returned to the Do constant control based on the PI calculation during normal operation.

〔Effect of the invention〕

As described in section 2 below, in the present invention, fluctuations in the sewage m flowing into the aeration tank are detected and control is performed to change the aeration air volume in advance. This makes it possible to suppress fluctuations in the aeration tank outlet DO caused by fluctuations in the sewage flowing into the aeration tank. When setting the aeration air volume in advance, windward correction is performed based on the set Do value and the measured value, so there is no risk that the measured value will deviate from the set value. Furthermore, since the air volume magnification is constantly updated, even if the quality of the inflowing sewage changes, the accuracy of estimating the required air volume can be maintained at a high level of accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a graph showing the relationship between the operation of the sewage pump and the flow rate of sewage flowing into the aeration tank, and FIG. 3 is a block diagram showing the configuration of a conventional control device. 1: Aeration tank 2: Do meter 3: DO controller 4: Air volume controller 5: Air volume meter 6: Electric valve 7: 9; ll: 12: 13: 14: 15: 16; 17: 18 Niblower 8: Li air Flower sewage flow meter setting DO value lO: setting aeration wind seal air flow rate magnification storage storage integral component calculation device inflow flow fluctuation detection device arrival time calculation device required aeration air flow estimation device aeration air h1 schedule device five aeration air flow setting device settings Aeration air volume switching command

Claims (1)

[Claims] 1. A PI control device with a DO meter installed in the aeration tank as the detection end and an aeration air flow rate controller as the operation end, an aeration tank inflow sewage flow meter, and an inflow volume that detects changes in the aeration tank inflow sewage volume. a fluctuation detection device, an arrival time calculation device that calculates the time it takes for the fluctuation in inflow amount to reach the installation point of the DO meter, and an air volume magnification storage device that stores the air volume magnification when the DO value is stable;
a required aeration air volume estimating device that estimates the required aeration air volume from the air volume magnification stored in the air volume magnification storage device and the amount of sewage flowing into the aeration tank, and a required aeration air volume estimating device that estimates the required aeration air volume from the air volume magnification stored in the air volume magnification storage device; The present invention is equipped with an aeration air volume setting device that determines the schedule for changing the aeration air volume so as to achieve the estimated required air volume, and an integral component calculation device that calculates the correction amount of the aeration air volume from the deviation between the measured value of DO and the set target value. Characteristic DO control device.