JPH0679717B2 - Return sludge amount control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a sewage treatment apparatus, and more particularly to a sewage amount control apparatus in a sewage treatment apparatus.

B. The present invention is performed by inflowing sewage into the aeration tank,
In the device for guiding the treated wastewater to the settling tank for treatment, a return sludge amount control device capable of controlling the return sludge amount with high accuracy by automatically calculating the control target value and constantly correcting it to an appropriate value is provided. I will get it.

C. Conventional technology In the activated sludge treatment process that treats sewage and factory wastewater, the activated sludge that is solid-liquid separated in the final settling tank is returned to the aeration tank through the return sludge circuit. Conventionally, the following method has been used to control the amount of returned sludge.

(1) Return method A fixed-quantity return method that returns the amount of sludge at a constant flow rate (for example, 500 m ³ / h).

(2) Flow rate control method that returns (k: Q _S ) at a fixed ratio (k) of inflow wastewater (Q _S : m ³ / h).

(3) MLSS (mixed liquor suspended solids concentration) operation control method, i.e. the return sludge concentration _{(C R: mg / l)} , the inflow wastewater use (Q _S: m ³ /
h), inflow SS concentration (C _P : mg / l), MLSS set value (C _A : mg / l) Calculate the amount of sludge to be returned (Q _R ) by, and control the amount of sludge to be returned to this value.

D. Problems to be Solved by the Invention In any of the above-mentioned methods, it is necessary to set a set value in the control device. In the case of quantitative return, the flow rate setting, ratio (k) in inflow water proportional control, and MLSS concentration become set values in the case of MLSS constant control and MLSS arithmetic control, respectively. The setting of these set values is usually decided based on the experience of the operator, but the set values will not be appropriate in the long term due to mutual interference with the excess sludge amount control, so it is necessary to correct the set values each time. I got it.

E. Means for Solving Problems The present invention solves the above-mentioned problems, and a mixed suspended matter concentration meter is installed in the aeration tank, and the time moving average value of this output is calculated, and at the same time. Set the moving average value of the set time at which the time is set as the mixed floating material set value of the returned sludge amount calculation formula,
The calculated mixed floating material set value is controlled so as to reach the target value.

Therefore, the return sludge target value is automatically corrected, and the excess sludge control and the return sludge amount control do not interfere with each other, and highly accurate return sludge amount control is performed.

F. Examples The present invention will be specifically described below with reference to Examples shown in the drawings.

In the drawing, 1 is an aeration tank and 2 is a final settling tank. The sludge settled in the final settling tank 2 is returned to the aeration tank 1 by the pump 3. Reference numeral 4 denotes a first arithmetic unit that receives the measured value of the MLSS meter (mixed material suspended solids concentration meter) 8 and calculates a moving average value corresponding to the time of the MLSS value. 5 is a return sludge amount calculating unit, return sludge amount of inflow wastewater quantity Q _S and return sludge meter 10 of the first moving average value C _A of the arithmetic unit 4 flows wastewater amount detector 9 C _R
Input these and calculate these. 6 is returned in the sludge flow rate control unit receives as input the return sludge amount C _R of the return sludge calculation unit 5 of the operation output value or the return sludge amount set value Q _Rset and return sludge quantity meter 11, controlling the pump 3. 7 is a limiter for setting the upper and lower limits of the amount of sludge to be returned.

In the control device having the above configuration, the output (MLSS value) from the MLSS meter 8 installed especially near the outlet in the aeration tank 1 is input to the moving average calculation device 4, and the average of the past 24 hours is sampled for the MLSS value. Calculate every step. Then, at a certain preset time, for example, at 10 am, the moving average value ( _CAset ) at that time is output to the returned sludge calculation device 5. In return sludge arithmetic unit 5, arithmetic expression _{Q R = (C Aset -C P} ) · Q S / the C _R of (C _R -C _Aset) in change to the new setting value, by the該演formula connexion return sludge Calculate the quantity Q _R. Here, the returned sludge concentration C _R , the inflow sewage utilization Q _S , and the inflow suspended substance concentration (inflow SS concentration) C _P are continuously measured from the process as in the MLSS meter 8 and input to the arithmetic unit 5. The return sludge amount _QRset calculated in this way becomes the target value of the return sludge amount control unit 6, and the rotation speed of the return sludge pump 3 or the return sludge control valve opening is adjusted so as to reach this value. In addition, the amount of sludge to be returned shall be limited by upper and lower limits.

When the aeration tank is a plug flow type, the installation position of the MLSS meter 8 should be on the aeration tank outlet side, which is less affected by fluctuations in the inflow load of the MLSS value. Further, the returned sludge concentration (C _R ) and the inflowing wastewater amount (C _P ) in the returned sludge calculation formula may be set to set values (for example, values close to target values).

According to the returned sludge amount control device according to the present embodiment, the conventional control method automatically sets the control target value set by human experience to an appropriate value, and the effect produced by this is It is as follows.

(1) Even if the initial target value setting is inappropriate, the target value is automatically corrected to the proper value. This correction is made gradually every day.

(2) The target value for returning sludge control changes depending on the amount of sludge in the sludge process (the amount of sludge in the system). That is, the control of the amount of sludge in the system and the control of the amount of returned sludge interfere with each other. Therefore, in the conventional method, if the setting of the surplus sludge control is changed, the control target value of the returned sludge amount control becomes inadequate, and the control may become impossible or may diverge.
However, according to the present invention, even in the above-mentioned case, the target value can be automatically corrected to a new target value and the adverse effect of mutual interference can be eliminated.

G. Effect of the Invention The present invention is as described above, and since the control target value is automatically calculated and always corrected to an appropriate value, there is no mutual interference between the various controls of the wastewater treatment device and high performance. It is possible to control the amount of returned sludge.

[Brief description of drawings]

The drawings are block connection diagrams of the returned sludge amount control device according to the embodiment of the present invention. 1 ... Aeration tank, 2 ... Sedimentation tank, 3 ... Return sludge pump,
4 ... Time moving average value calculation unit, 5 ... Returned sludge amount calculation unit, 6 ... Returned sludge flow rate control unit, 7 ... Limiter, 8 ...
… MLSS meter, 9 …… Inflow sludge meter, 10 …… Return sludge concentration meter, 11 …… Return sludge meter.

Claims (1)

[Claims] 1. A treatment device for treating sludge by inflowing sewage into an aeration tank, and guiding the treated sewage to a settling tank for treatment, wherein the time of concentration of mixed suspended solids of sewage in the aeration tank A calculating means for calculating a moving average value, a returning sludge amount calculating means for calculating a returning sludge amount at a predetermined set time of a predetermined time according to the time moving average value of the mixed suspended matter concentration, and the returning A returned sludge amount control device, which is configured by means for controlling the returned sludge amount returned from the settling tank to the aeration tank with the returned sludge amount calculated by the sludge amount calculation means as a target value.