JP2950661B2 - Control unit for water treatment plant - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control apparatus for a water treatment plant having an aeration tank and a sedimentation tank, and more particularly to a control apparatus for a water treatment plant capable of stabilizing the DO concentration in the aeration tank.

[0002]

2. Description of the Related Art Generally, a water treatment plant has an aeration tank for treating wastewater such as general sewage and organic wastewater using activated sludge. Raw water (sewage) flowing into the aeration tank is aerated by a blower connected to the aeration tank, is bio-oxidized, and is solidified as sludge. Thereafter, these solids are separated from water in the sedimentation basin to be clarified.

In such a water treatment plant, the effect of purification, the stability of operation, and the energy consumption are determined by the conditions of aeration, that is, the DO concentration (dissolved oxygen concentration) of the aeration tank. That is, it is necessary to maintain the DO concentration in the aeration tank at a constant value in order to enhance the effect of purification and prevent excessive aeration to reduce the energy consumption of the blower.

Conventionally, as a control method for maintaining the DO concentration in the aeration tank at a constant value, a DO concentration meter is provided in the aeration tank, and the blower volume of the blower is automatically adjusted so that the indicated value becomes a target value. Is used. In this feedback control method, a cascade control method in which the control output is corrected by the flow rate of raw water is also used. Further, in the feedback control method or the cascade control method, the deviation of the DO concentration (the difference between the target value of the DO concentration and the indicated value of the DO concentration meter), which is the control input, is determined by another process value of the aeration tank, for example, the concentration of suspended solids. There is a control method for correcting.

[0005]

However, these control methods are all based on feedback control by a PID controller or the like, and there is necessarily a response delay. Therefore, when fluctuations in the flow rate of raw water, the concentration of organic substances, or the concentration of toxic substances to activated sludge organisms, that is, the disturbance of control is relatively small, the response delay can be compensated in a sufficiently short time, but heavy rain or snowfall etc. When these disturbances are large and the fluctuation range is high, a transient response occurs. If the disturbance is large, overshoot and vibration phenomena appear, and the biological activity in the activated sludge becomes abnormal due to the incorporation of toxic substances in the raw water.
In some cases, the O concentration cannot be controlled to the target value.

Further, as a method of controlling the DO concentration to be constant, two or more DO concentration meters are installed at different positions in the downflow direction of the aeration tank, and feedback control is performed by the downstream DO concentration meter while the upstream DO concentration meter is controlled. A method of correcting the feedback output of the downstream DO densitometer based on the fluctuation of the indicated value of the DO densitometer can be considered. However, the control method requires a large number of DO densitometers, so that it is expensive and maintenance is complicated.

The present invention has been made in view of the above points, and provides a water treatment plant control device capable of stabilizing the DO concentration in an aeration tank even when various environmental conditions fluctuate. The purpose is to do.

[0008]

SUMMARY OF THE INVENTION The present invention provides a raw water flow meter, an organic matter concentration meter, and an SS concentration meter provided in a raw water inflow path to an aeration tank to be aerated by a blower, and a downstream side of the aeration tank. Return flow meter and return concentration meter provided in the return sludge pipe from the sedimentation basin to the aeration tank, and signals from these raw water flow meter, organic matter concentration meter, SS concentration meter, return flow meter and return concentration meter A process simulator for predicting the oxygen utilization rate and the DO concentration in the aeration tank based on the DO simulator and a DO concentration measured by the DO concentration meter provided in the aeration tank and the DO concentration predicted by the process simulator. Calibrating means for calibrating the oxygen utilization rate measured, and a value obtained by correcting the DO concentration measured by the DO concentration meter with the oxygen utilization rate calibrated by the calibration means. A control device for water treatment plants, characterized in that a controller for controlling the air volume of the blower are.

[0009]

The process simulator predicts the oxygen utilization rate and the DO concentration in the aeration tank based on signals from the raw water flow meter, the SS concentration meter, the return flow meter, and the return concentration meter. Calibration means is used to calibrate the oxygen utilization rate from the DO concentration measured by the densitometer and the DO concentration predicted by the process simulator, and is corrected using the DO concentration measured by the DO concentration meter and the oxygen utilization rate after the calibration,
The controller controls the air volume of the blower based on the corrected value.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 to 3 are diagrams showing an embodiment of a control device for a water treatment plant according to the present invention. In FIG. 1, raw water flows into the aeration tank 4 from a raw water inflow channel 31.

A diffuser 7 is provided in the aeration tank 4, and a blower 6 is connected to the diffuser 7 via an air blower 32. Further, a suction pipe 35 is connected to the blower 6,
An air flow meter 5 is provided in the suction pipe 25. In addition, a DO concentration meter 9 is installed near the outlet of the aeration tank 4.

Downstream of the aeration tank 4, a sedimentation basin 8 is disposed via a communication path 33. Between the bottom of the sedimentation basin 8 and the entrance of the aeration tank 4, sludge in the sedimentation basin 8 is aerated. A return sludge pipe 34 for returning into the tank 4 is connected. Return sludge pipe 3
4, a return pump 10 is attached.

A raw water flow meter 1, an organic matter concentration meter 2, and an SS concentration meter 3 are sequentially provided in the raw water inflow passage 31, and a return flow meter 11 and a return concentration meter 12 are provided in a return sludge pipe 34. They are arranged sequentially.

A raw water flow meter 1, an organic matter concentration meter 2, S
The S concentration meter 3, the return flow meter 11, and the return concentration meter 12
Each is connected to the process simulator 13.
The process simulator 13 predicts the oxygen utilization rate and the DO concentration in the aeration tank 4 based on signals from the raw water flow meter 1, the organic matter concentration meter 2, the SS concentration meter 3, the return flow meter 11, and the return concentration meter 12. Things. The DO concentration meter 9 in the aeration tank 4 is provided with a process simulator 13.
The DO concentration meter 9 is also connected to a controller 15 for calibrating the oxygen utilization rate predicted by the above. The controller 15 controls the air volume of the blower 6 based on a value obtained by correcting the DO concentration measured by the DO concentration meter 9 with the calibrated oxygen utilization speed from the process simulator 13. The controller 15 includes an air flow meter 5 and a blower 6
Are connected to each other.

Next, the operation of this embodiment having the above-described configuration will be described. During operation of the water treatment plant, first, the flow rate of raw water, the organic substance concentration, and the SS concentration are measured by the raw water flow meter 1, the organic matter concentration meter 2, and the SS concentration meter 3. At the same time, the flow rate and concentration of the returned sludge are measured by the return flow meter 11 and the return concentration meter 12, and these signals are input to the process simulator 13. Next, in the process simulator 13, the oxygen utilization rate and the DO concentration in the aeration tank 4 are predicted as follows. The operation in the process simulator 13 will be described in detail.

That is, in the process simulator 13, a substrate model representing the oxidation of organic substances as shown in FIG. 2A and a mixed model of the aeration tank as shown in FIG. I have. FIG The 2 matrix model shown in (a), the raw water suspendable organic 16 (concentration X _o) and adsorption to activated sludge following formula dissolved organic matter 17 (concentration S _o) (1)
And (2).

[0017]

(Equation 1) Here, _Sa is the concentration of the active substrate 18 in FIG. 2A and is a state variable of the process simulator.

The dissolved organic matter d reduced by the formula (2)
Part of the S p _/ dt is directly assimilated substrate at a rate given by Equation some other becomes adsorption substrate (3).

[0019]

(Equation 2) Here, k _oc is the direct assimilation rate.

The absorbed suspended substrate 21 (concentration S _s ) is hydrolyzed and distributed according to the formula (4) and is added to the adsorbed substrate 19 (concentration S _d ).

[0021]

(Equation 3) The adsorption substrate 19 (concentration S _d ) is calculated from the formula (5) as
(Concentration S _c ).

[0022]

(Equation 4) Next, the assimilation substrate 20 is used for the propagation of the activated sludge organism, and is converted into the activated substrate 18 (concentration S _a ) according to the equation (6).

[0023]

(Equation 5) Here, μ is the maximum growth rate of activated sludge, and K ^s is the saturation constant of the Monod equation.

The active substrate 18 (concentration S _a ) is inactivated to become the inactive substrate 22, a part of which is killed and the dissolved organic matter 17 (concentration S _o ) is increased by the formulas (7) and (8). It becomes S _o .

[0025]

(Equation 6) Here, _Kao is the solubilization rate.

Further, as shown in FIG. 2 (b), the mixed model of the aeration tank in the process simulator 13 divides the aeration tank 4 into a predetermined number in the flow direction, and
The ratio of the complete mixed flow in 24b is α, and the ratio is represented by two flows of a short-circuit flow that passes through the divided tank without undergoing complete mixing and complete mixing. The biooxidation described above is intended to take place only in this perfectly mixed stream.

Further, the calculation of the DO concentration and the oxygen utilization rate Rr is performed as follows. That is, in the model in which the substrate changes as shown in FIG. 2A, the path through which dissolved oxygen 23 is consumed is a direct path of assimilative assimilation and inactivation, and the oxygen utilization rate R _r is _calculated by the equation (9). Predict.

[0028]

(Equation 7) K _qd , K _qc , K _qa , and K _qi are the respiratory quotients in the pathway of each substrate conversion. Here, the respiratory quotient refers to the amount of oxygen per unit substrate required when the substrate is converted.

The concentration of the adsorbed substrate S _d , the concentration of the assimilating substrate S _c , the concentration of the fouling substrate S _a , the concentration of the suspended substrate S _s, and the concentration of the inactive substrate S _{i shown} in FIG. signal Q _s, signal _{S s} of toll concentration meter, SS concentration of the signal X _o, signal X of the signal Q _r and return densitometer of the return flow meter
Based on _r , it can be obtained using a predetermined calculation formula.

When the oxygen utilization rate _Rr is determined, the DO concentration C
_s is predicted by the material balance with the supply of the dissolved oxygen concentration C _pv . That is DO concentration C _s by aeration formula (10)
(11) Predicted by (12).

[0031]

(Equation 8) Here, K _la is the overall oxygen transfer coefficient, k and n are plant constants, and _CT is the saturated DO concentration of pure water at the water temperature T ° C.

By using the equations (1) to (12) stored in the process simulator 13 and identifying the parameters in these equations, the DO of each of the divided tanks in the aeration tank that fluctuates every moment is identified. and concentration C _s and an oxygen utilization rate R _r, it can be predicted online. However, since these parameters, particularly the respiratory quotient in the equation (9) cause diurnal and seasonal variations depending on the composition of the organic matter in the raw water and the type of activated sludge organisms growing in the aeration tank, the oxygen utilization rate R The prediction of _r may be significantly shifted. Therefore, equation (13) is used to calibrate the oxygen utilization rate by multiplying the entire right side of equation (9) by the respiratory quotient coefficient K _qr.
think of.

[0033]

(Equation 9) This K _qr is obtained by the calibration means 14 so that the predicted value of the DO concentration of the divided tank in which the DO concentration meter 9 is installed and the DO concentration actually measured by the DO concentration meter 9 become the same value.

[0034] That is, in the calibration means 14, the deviation △ C between the signal C _pv and, of split vessel in DO concentration meter 9 the location of predicted by the process simulator 13 DO concentration estimated value C _s from the DO concentration meter 9 Occurs, the respiratory quotient coefficient K _qr is calculated by the formulas (14), (15), and (16) every calculation cycle of the process simulator 13 (one minute in this embodiment).
To obtain the corrected value.

[0035]

(Equation 10) In equation (15), A _qr is a correction gain, and equation (1)
In 6), K _qrn is the current respiratory quotient,
_qrn-1 is the previous respiratory quotient coefficient.

Next, the controller 15 mainly performs PI control using the signal C _pv of the DO densitometer 9 as a feedback signal.
The oxygen utilization rate R _r that is calibrated at 4 for controlling the blower 6 sends a control output MV correction to the output deviation of the PI control to the blower 6.

The equations in the controller 15 in this case are shown in equations (17) to (20).

[0038]

[Equation 11] In Equations (17) to (20), n and n-1 are the current control time and the previous control cycle time, and ΔE (n) is the input deviation 1 K _c and K _r are weighting factors (usually 1.0). It is.

The air volume of the blower 5 can be controlled by changing the rotation speed of the blower 5 or opening and closing a suction valve (not shown) of the blower 5. The air volume of the blower 5 is actually measured by the air volume meter 5, and the signal of the air volume meter 5 is sent to the controller 15.

[0040] In this case, the control output MV from the controller 15 (n) as shown in equation (21) may also be a control output MV that cascade control with the raw water flow meter 1 signal Q _s .

[0041]

(Equation 12) Next, effects of the control device of the present invention will be described.

FIG. 3 is a diagram showing the effect of the present invention. FIG.
(A) shows the flow rate Q _{s of} raw water flowing into the aeration tank, that is, the pattern of load fluctuation. FIG. 3 (b) and (c)
3A and 3B are diagrams respectively showing the DO concentration in the aeration tank when controlled by the control device of the present invention and when controlled by the conventional control device in the load variation pattern as shown in FIG.

The control device of the present invention shown in FIG.
The signal C _pv of O densitometer performs PI control of a feedback signal, is corrected by the oxygen utilization rate after calibration it is obtained by cascade control with more raw flowmeter signal Q _s.

[0044] On the other hand, the conventional control device shown in FIG. 3 (c), performs PI control to the feedback signal DO concentration C _pv, is obtained by cascade control with this raw water flow meter signal Q _s.

As shown in FIG. 3, according to the control device of the present invention (FIG. 3 (b)), the signal C _pv of the DO concentration meter is corrected based on the calibrated oxygen utilization rate, thereby obtaining the conventional control device. As compared with (FIG. 3 (c)), extremely stable DO concentration control can be performed.

[0046]

As described above, according to the present invention,
Extremely stable DO concentration control can be performed by correcting the DO concentration measured by the DO concentration meter using the oxygen utilization speed after calibration and controlling the air volume of the blower based on the corrected value.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one embodiment of a control device for a water treatment plant according to the present invention.

FIG. 2 is a diagram showing an operation in a process simulator.

FIG. 3 is a diagram showing the effect of the control device of the water treatment plant according to the present invention in comparison with a conventional control device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 raw water flow meter 2 organic matter concentration meter 3 SS concentration meter 4 aeration tank 5 air flow meter 6 blower 8 sedimentation basin 9 DO concentration meter 11 return flow meter 12 return concentration meter 13 process simulator 14 calibration means 15 controller

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C02F 3/12

Claims (1)

(57) [Claims] 1. A raw water flow meter, an organic matter concentration meter, and a SS provided in a raw water inflow passage to an aeration tank to be aerated by a blower.
A concentration meter, a return flow meter and a return concentration meter provided in a sludge pipe returned from the sedimentation tank installed downstream of the aeration tank to the aeration tank, and a raw water flow meter, an organic matter concentration meter,
A process simulator for predicting the oxygen utilization rate and the DO concentration in the aeration tank based on signals from the S concentration meter, the return flow meter and the return concentration meter; and a DO provided in the aeration tank.
Calibration means for calibrating the oxygen utilization rate predicted by the process simulator from the DO concentration measured by a densitometer and the DO concentration predicted by the process simulator;
A controller for controlling the air volume of the blower based on a value obtained by correcting the DO concentration measured by the DO concentration meter with the oxygen utilization rate calibrated by the calibrating means. apparatus.