JPS59222298A - Method for controlling filthy water treating plant - Google Patents

Abstract

PURPOSE:To control stably concn. of dissolved oxygen (DO) and the amt. of total activated sludge by interlocking the control of flow rate of feed air to an aeration tank and the control of flow rate of returned sludge from a settling basin, and compensating interference of the low rate of the feed air and the flow rate of the returned sludge with each other. CONSTITUTION:Filthy water is introduced into an aeration tank 1-1 through a channel passage A, and a mixture of the filthy water and the activated sludge flowed therefrom is introduced into a settling basin 1-2 through a channel passage A1, and the solid component is separated from the liquid, and the supernatant liquid is discharged through a channel passage A2. A part of the activated sludge 1-8 precipitated in the settling basin 1-2 is withdrawn through a drawing pipe 1-9, and a part of the drawn sludge is returned to the aeration tank 1-1 through a channel passage B, and a part thereof is discharged through a channel passage C to the outside as excess sludge. Air is fed to the aeration tank 1-1 from an air feeding device 1-5 through an air dispersing device 1-6, and the flow rate of the feed air QA* is controlled to a set value QA by a controller 5.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for controlling a sewage treatment plant that is equipped with an aeration tank and a settling tank and performs secondary treatment of sewage by an activated sludge method, and particularly relates to a method for controlling a sewage treatment plant that is equipped with an aeration tank and a sedimentation tank and performs secondary treatment of sewage by an activated sludge method. This relates to method I: l-, which continuously studies and controls the flow rate of sludge and the flow rate of sludge returned from the settling tank.

[Technical background of the invention and its problems] Sewage that has undergone primary treatment such as pre-sedimentation is not sent to an aeration tank, but is aerated while being mixed with activated sludge and subjected to secondary treatment. It is sent to the settling pond along with the sludge.

The treated sewage is separated into solid and liquid in a settling tank, the top water is taken out to the outside, solids and activated sludge are settled in the settling tank, and part of the activated sludge is returned to the aeration tank.

After t', excess sludge is discharged to the outside.

In the above secondary treatment, in order to efficiently purify sewage C1 (- is the air flow rate QA to the aeration tank + the return sludge flow needle Qn from the settling tank (hereinafter referred to as the return flow rate), and the excess sludge withdrawal flow rate Qw (hereinafter referred to as the withdrawal flow rate) must be appropriately controlled.

However, since the operations of the three control variables and the mutual forces interfere with each other, comprehensive control is safe, but in conventional methods, sufficient consideration is not given to mutual interference.

[Object of the invention] The present invention controls the air flow itQm and the return flow rate QR in conjunction with each other, thereby increasing the dissolved oxygen concentration (hereinafter referred to as D) in the aeration tank.
The purpose of the present invention is to provide a control method for a sewage treatment plant that is capable of stabilizing and highly accurate C control.

[Summary of the Invention] The present invention provides a control method for a sewage treatment plant that is equipped with an aeration tank and a settling tank and performs secondary treatment of wastewater by an activated sludge method, in which DO9 degree in the aeration tank is compared with a target DO concentration. a first controller that outputs a primary setting value of the air flow rate; a second controller that compares the sludge amount in the sedimentation tank with a target sludge amount and outputs a return sludge flow rate; A compensation calculator is provided which calculates the secondary setting values of the air blowing flow rate and the return sludge flow rate by inputting each of the secondary setting values of 1゛ and performing a predetermined calculation that interlocks the two. The flow rate and the return sludge flow rate are controlled, thereby preventing the mutual interference between the blast flow and the return flow, and reducing the DOg%j within 1 + 1 and the total activated sludge. It is controlled at a constant rate.

[Embodiments of the invention] An embodiment of the present invention is shown in FIG.

In FIG. 12, 1 is a sewage treatment plant that performs secondary treatment, and sewage flows through pipe A into an aeration tank 1-1.

The mixed liquid of sewage and activated sludge flowing out from the aeration tank 1-1 flows into the sedimentation tank 1-2 through the pipe A1 [7] where it is separated into solid and liquid, and the supernatant liquid is discharged through the pipe A2.

In addition, activated soil/IP precipitated in settling tank 1-2, 1-8
A part of the water is drawn out through the drawing pipe 1-9, a part of which is returned to the aeration @1-1 through the pipe B, and a part of which is sent to the pipe C
It passes through the sludge and is discharged outside as surplus sludge.

In addition, at the aeration pulse 1-IC, air is sent from the ventilation unit 1-5 through the diffuser 1-6, and the air flow rate for 9 people is determined by the controller 51-, so the set value QA*l2. A return device 1-1f) is provided in the conduit B, and the controller 6 controls the return flow rate QR to a set value 1.

Further, a surplus drawing device 1-13 is provided in the conduit C, and the drawing flow rate "QW" is adjusted by this.

In addition, a DO concentration meter ]-7 is installed in the interior C2 of the aeration tank 1-1, and the detected Do concentration is inputted by the first controller 21.

In addition, the pipe operator has an inflow sewage flow meter 1-3 and an inflow sewage concentration meter 1-4, pipe B has a return sludge flow meter 1-II, and a return sludge concentration meter 1-12, and the pipe wIC has a surplus sludge flow meter 1-2. A total of 1 to 14 extraction flows are provided, and their detection signals Q
s+ The second controller 3
is input.

The first controller 2 compares the detected fcDoJ degree DO with a preset target concentration DO*, and sequentially outputs the primary setting value S2n of the air flow rate through the following calculations.

E -DO book-1) O------(1')n l △s1n=xclp(gln"1(n-1))"'I
',, ,E,n,,,(2)Sin = ”'l (
n-1) + △sln --- (81 where Kl
p+ llb TI I is a control constant.

In addition, in the second system @ 1 unit 3, the sedimentation basin sludge needle BS is compared with the preset target sedimentation basin sludge age BS*, and the following calculation is performed to return i# and the primary set value S2n of the amount to the j visceral output. be done.

E, n=B8*-BS, --------(4)8s
n-82(n-1)+△8. n------<a) Here, K11I'+ h2+ T2 is a control constant.

The above-mentioned -order setting values S1n and SBn (hereinafter referred to as sl and s2) are obtained by the first calculation circuit 11 of the compensation calculation unit 7,
1: ((Two people are working, each setting constant AI, B1
．． A2. The following calculation is performed using B2.

The above output signals 'DI+DS1 and 81.8g are further;
- The signals are input to the second input circuit 12 and 14, and the following calculations are performed respectively.

QA*= (1+Di) 81 -------
(9) Qn*-(1+DB) Sn ------
The above output signals QA* and Q- are the secondary set values and are input to the controller 5.6, respectively, and the air flow rate QA is
And the return flow rate QR is controlled to the above secondary set value.

Using the method described above, the set value QA* of the air flow ml and the set value QR* of the return needle are calculated using equations (B) and (6), respectively.
The primary setting value S1 calculated from the formula I7. The values are interlocked with each other when S2 is assembled.

For example, Qh' becomes the following equation from equations (8) and (9).

In other words, compared to Q person*ke SI, it is 11 and 820J
Assuming that the proportional coefficient is reduced by Soka C2, and thereby the air flow rate QA is controlled in conjunction with the return flow rate QR.

The same applies even if there are two QR*.

Next, the specific effects brought about by the control device of the present invention will be explained using the response Vt to fluctuations in the flow rate of sewage water, which is the main disturbance in an activated sludge method sewage treatment plant.

Figure 2 shows the control of the sewage flowing into the aeration tank (1) when the loss suddenly increases, the conventional method of controlling the DO concentration at a constant level, and the independent control of the sedimentation pond sludge center (1). 1'- without interlocking
When operating the air flow amount and return amount, and the difference in direction μm of the present invention
This is a graph of the results of rear driving compared to the case of driving at ■7.

Figure 2 (A) 14 IHI change when sewage flows in, (B
) is the change in the DO concentration in the aeration tank, and (C) is the change in the amount of sludge present in the settling pond. (a) is the result obtained by the conventional method, and (b) is the result obtained by the control method of the present invention. This is the result.

In conventional control methods, the amount of air blown increases to keep up with the increase in the amount of inflowing sewage, but as the amount of returned water also increases, the DO concentration rapidly decreases, and when there is a shortage of sewage, the amount of air blown decreases. In addition, although the amount of returned air is reduced, the response is delayed (as a result, the inverse (2)O concentration increases, resulting in an overaerated state).

Although the fluctuation of the amount of sludge existing in settling tank C2 is accompanied by small fluctuations in the conventional method, the deviation from the target value is smaller than the control result according to the present invention. It can be seen that the response is no longer subject to interference because the return sound control is related to the Do concentration as described above, and its control characteristics are greatly improved.

[Effects of the Invention] As explained above, according to the present invention 1'', in a sewage treatment plant that is equipped with an aeration tank and a settling tank and performs secondary treatment of wastewater by the activated sludge method, it is possible to control the air flow rate to the aeration tank and It is controlled in conjunction with the return sludge flow rate control from the settling tank, thereby compensating for mutual interference between the air blowing flow rate and the return flow rate, and stably controlling the DO concentration in the aeration tank and the overall activated sludge flow. A rational method for controlling sewage treatment plants is provided.

[Brief explanation of drawings]

Fig. 1 is a plant system diagram showing one embodiment of the present invention;
(1 is a graph showing an example of the effects of the present invention.0 1 Sewage treatment plan l-2, 3 controller 1 unit 4 sludge amount simulator 5.6 Controller 7 Compensation calculator 11~
I4 Arithmetic circuit 1-1 Aeration tank 1-2 Sedimentation tank 1-3 Inflow sewage concentration needle 1-4 Inflow sewage concentration needle 1-5 Air blower 1-6 Aeration equipment 1-7 DO gameter 1-8 Activated sludge 1-9 Drawing pipe 1-10 Returning device 1-11 Return sludge flow meter 1-12 Return sludge daughter flow meter 1-13 Excess drawing device 1-14 Extra aim I drawing flow meter Fig. 1 Fig. 2

Claims (1)

[Claims] In a control method for a sewage treatment plant that uses an aeration tank and a settling tank and performs secondary treatment of sewage using an activated sludge method,
A first controller that compares the Do concentration in the aeration tank with the target Do concentration and outputs a primary setting value of the air flow rate, and compares the amount of sludge in the settling basin with the target sludge firewood to determine the return sludge flow rate. A second controller that outputs the set value of the air flow h↑ and the flow rate of the returned sludge, and a predetermined operation in which the set values of the air flow h↑ and the flow rate of the returned sludge are input and the two are linked. 1. A control method for a sewage treatment plant, comprising: providing a compensation calculator for outputting secondary setting values of the flow rate, and controlling the air flow rate and return sludge flow t in accordance with each of the secondary setting values.