JP2002219481A - Equipment for controlling concentration of dissolved oxygen in aerating tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide equipment for controlling an aerating tank which can stabilize the concentration of dissolved oxygen in the aerating tank to provide stable treatment performance even if the quality of inflowing water changes, and a method for controlling the dissolved oxygen in the aerating tank using this equipment. SOLUTION: This equipment for controlling the concentration of dissolved oxygen in the aerating tank for treating wastewater includes a flowmeter and control valve for the raw water fed to the aerating tank, a return sludge flowmeter, a dissolved oxygen analyzer, a pressure sensor for the pressure in the aerating tank, a pressure control valve and pressure controller, an oxygen feed rate control valve and measuring instrument, a neural net optimizer for predicting the concentration of dissolved oxygen over the long term based on input process data and calculating the target value, a short term predictive PID controller for the concentration of the dissolved oxygen, and an oxygen feed rate controller.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control apparatus and a control method of a dissolved oxygen concentration in an activated sludge aeration tank used in a general wastewater treatment plant and a sewage treatment plant such as a chemical factory.

[0002]

2. Description of the Related Art In a wastewater treatment process by the activated sludge method, a method of oxidizing and decomposing organic matter in an aeration tank, coagulating sludge as necessary, and then separating and separating the same in a sedimentation tank to obtain treated water is generally used. It is a target. In particular, in many cases, a closed aeration tank is used for treating high-load wastewater in a chemical factory or the like.

In this treatment, the supply of oxygen to the aeration tank is usually performed by measuring the flow rate of raw water supplied from a pretreatment facility from a raw water neutralization tank or a first settling tank, and based on the measured flow rate. Adjust the oxygen supply so that the pressure of
It is performed by dissolving oxygen in water by stirring in a tank. Adjustment of the amount of oxygen in the aeration tank to an appropriate range is performed by adjusting the discharge valve of the exhaust pipe to discharge exhaust gas out of the system according to the oxygen concentration of the gas phase in the aeration tank. Have been done.

However, if such oxygen supply is adjusted based on the internal pressure of the aeration tank and the oxygen concentration, the following can be obtained: "lower oxygen concentration in the gas phase of the aeration tank → opening of the pressure control valve in the aeration tank → lower pressure in the tank → oxygen supply amount. Control valve open → Oxygen supply → Oxygen concentration rise in tank → Aeration tank pressure control valve closed → Tank pressure rise → Oxygen supply amount control valve closed →
The cycle of "lower oxygen concentration" is repeated, the control is not stabilized, and the dissolved oxygen concentration in the aeration tank is not stable. Also, since we ignore the quality of the raw water supplied,
Processing results were also unstable.

[0005]

SUMMARY OF THE INVENTION A control device for an aeration tank which can stabilize the concentration of dissolved oxygen in the aeration tank and therefore can provide a stable treatment result even when the quality of the inflowing water changes, and an apparatus using the same. Provided is a method for controlling the concentration of dissolved oxygen in an aeration tank.

[0006]

The gist of the present invention is to provide an oxygen supply pipe, a raw water supply pipe, a return sludge receiving pipe, an exhaust pipe,
And a control device for a dissolved oxygen concentration of an aeration tank (4) for wastewater treatment provided with a discharge pipe to a settling tank for treated water / sludge, the control device including the following instrumentation equipment.

A) Raw water flow meter (1) for measuring the flow rate of raw water supplied to the aeration tank and a raw water flow control valve (2) b) Return sludge flow meter (3) for measuring the flow rate of sludge returned from the sedimentation tank C) a dissolved oxygen concentration meter for measuring the dissolved oxygen concentration in the aeration tank (5) d) a pressure detector for measuring the internal pressure of the aeration tank (6) e) evacuation of the aeration tank to adjust the internal pressure of the aeration tank A pressure control valve (7) and a pressure control controller (1
2) f) Oxygen supply amount control valve (9) for adjusting the amount of oxygen supplied to the aeration tank g) Oxygen supply amount measurement device (8) installed immediately near the oxygen supply amount control valve (9) of the oxygen supply pipe h) By inputting predetermined process data,
Neural net optimizer (1) that performs long-term prediction of dissolved oxygen concentration and calculates the target value of dissolved oxygen concentration
3) i) P with short-term prediction function for calculating the amount of oxygen to be supplied based on the measurement result of the dissolved oxygen concentration meter and the target value of the dissolved oxygen concentration calculated by the neural net optimizer
ID control device (11) j) Based on the measurement result of the oxygen supply amount measuring device (8) and the oxygen amount to be supplied indicated by the PID control device with short-term prediction function (11), the oxygen supply amount adjusting valve (9) Oxygen supply controller (10)

[0008] The gist of the present invention is to provide a short-term prediction function P
As a predictive model of the ID control device, there is also a control device of the dissolved oxygen concentration of the aeration tank using a discrete linear model that takes into account the dynamic characteristics of the dissolved oxygen concentration with respect to the oxygen supply amount and noise, and as process data, Raw water temperature, flow rate,
Hydrogen ion concentration (pH), chemical oxygen demand (CO
D), Biochemical oxygen demand (BOD5), suspended solids (SS), aeration tank temperature, pressure, dissolved oxygen concentration, mixed liquid suspension in tank (MLSS), mixed liquid volatile suspension in tank The present invention also provides a control device for the dissolved oxygen concentration in the aeration tank, which uses at least one kind of data selected from the group consisting of substances (MLVSS).

Another aspect of the present invention is a method for controlling the concentration of dissolved oxygen in an aeration tank using the above-described dissolved oxygen concentration control apparatus, and the method for controlling the concentration of dissolved oxygen in an aeration tank using oxygen having a purity of 50% or more as oxygen to be supplied. There is also a method for controlling the dissolved oxygen concentration.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The control device of the present invention uses the target dissolved oxygen concentration of the aeration tank determined by the long-term, multivariable and non-linear prediction optimization calculation as the target value of the short-term linear prediction control, and determines the required oxygen in the aeration tank. Calculates the amount of oxygen and adjusts the supply of oxygen based on this.This is used to prevent excessive supply of oxygen and to prevent temporal fluctuations caused by unsteady fluctuation factors and process disturbances. Even if water is generated, stable water treatment is performed.

The neural net optimizer used in the control device of the present invention learns in advance the relationship between the process data during the past operation and the dissolved oxygen concentration and, based on this, learns the oxygen data from the process data during the operation. Consumption,
Calculates the target value of dissolved oxygen concentration that can optimize cost functions related to wastewater treatment volume, wastewater quality, etc., and calculates this target value with a PID controller (Predictive PID Control
ller). Here, process data which are variables to be input in the neural net optimizer of the apparatus of the present invention include raw water temperature, flow rate, hydrogen ion concentration (pH), and chemical oxygen demand (CO
D), Biochemical oxygen demand (BOD5), suspended solids (SS), aeration tank temperature, pressure, dissolved oxygen concentration, mixed liquid suspension in tank (MLSS), mixed liquid volatile suspension in tank It is preferable to use at least one kind of data selected from the group consisting of substances (MLVSS). It is preferable to input these data together with the upper and lower limit values.

Incidentally, these process data can be measured by an ordinary method or based on JIS K0102 or the like. Further, in a facility for treating wastewater from a plurality of plants, for example, a centralized wastewater treatment facility of a chemical factory, it is preferable to individually measure the flow rate, pH, COD, etc. of the wastewater from each plant. is there. The process data to be input is not limited to the above.

The neural net optimizer used in the apparatus of the present invention preferably has a three-layer structure having an input layer, a middle layer, and an output layer. If the number of layers is two, the nonlinear model cannot be handled. On the other hand, if the number of layers is four or more, the model becomes too complicated and “training” of the model takes too much time, and the practicality tends to decrease.

Further, in the apparatus of the present invention, the neural network optimizer is used to calculate the dissolved oxygen concentration, for example, 1%, from the various process data described above, taking into account the upper and lower limits of each variable and the cost function. The target value of the dissolved oxygen concentration that enables cost optimization by predicting the long-term response from
D control device.

The PID control device with a short-term prediction function used in the present invention is obtained by adding a short-term model prediction function to an ordinary PID control device. Specifically, using the operation data indicating the relationship between the dissolved oxygen concentration in the past and its target value and the set value of the oxygen supply amount, the future transition of the dissolved oxygen concentration is calculated using a linear model of the controlled object. That is. As the linear model to be controlled, it is preferable to use a discrete linear model (ARIMAX model) that takes into account the dynamic characteristics of dissolved oxygen concentration with respect to the oxygen supply amount and noise. The ARIMAX model is called “Auto Regressive
"Integrated Mov-ing Average eXogenous model" (autoregressive integral moving average exogenous variable model).

In the apparatus of the present invention, the PID controller having such a short-term prediction function is capable of dissolving at least 3 to 8 hours ahead using the signal taken from the dissolved oxygen concentration meter and the above linear model. By comparing the predicted value of the oxygen concentration with the target value of the dissolved oxygen concentration indicated by the aforementioned neural net optimizer, and adjusting the supply amount of oxygen so as to reduce the deviation, the dissolved oxygen concentration can be reduced. To control.

Since the PID control device with the short-term prediction function can incorporate a statistical model capable of approximating the dynamic characteristics of the concentration of dissolved oxygen to be controlled, the process in which the dead time is long and changes, and It shows good control performance even for processes with long time constants.
In addition, by considering the noise model, it is possible to maintain good control performance without adjusting the parameter values of the model even for process disturbance.

It is to be noted that a dissolved oxygen concentration meter that emits a signal of the dissolved oxygen concentration to the PID control device having the short-term prediction function is installed near the outlet from which sludge and treated water flow out of the aeration tank. It is preferable for grasping. The method of the present invention uses the control device described above, and as described above,
Preferably, the dissolved oxygen concentration in the closed aeration tank is controlled.

The supply amount of oxygen is automatically changed by the output of the PID controller having the short-term prediction function, and the flow rate set value of the oxygen supply controller is automatically changed. And controlling the oxygen supply amount control valve. The oxygen used in the method of the present invention preferably has high purity in terms of processing efficiency and control responsiveness. As its purity, the oxygen content is 50
% Or more, preferably 70% or more, more preferably 90%
Above, more preferably 95% or more.
As the aeration tank to which the control device and the control method of the present invention are applied, a closed aeration tank is suitable from the viewpoint of efficient use of supplied oxygen.

[0020]

The embodiments of the present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the present invention. FIG. 1 shows a closed aeration tank (4), a raw water flow meter (1) for measuring the flow rate of raw water flowing into the tank, and a flow control valve (2) thereof, and the flow rate of sludge returned from the sedimentation tank. Return sludge flow meter (3), dissolved oxygen concentration meter (5) for measuring the dissolved oxygen concentration in the aeration tank, pressure detector (6) for measuring the internal pressure of the aeration tank, pressure provided on the exhaust pipe of the aeration tank A regulating valve (7), a pressure control controller (12), an oxygen supply amount regulating valve (9) for regulating the flow rate of oxygen supplied to the aeration tank, an oxygen supply amount measuring device provided immediately adjacent to the oxygen supply amount regulating valve (8) Raw water temperature, flow rate, hydrogen ion concentration (pH) and chemical oxygen demand (COD), biochemical oxygen demand (BOD5), suspended solid (SS), aeration tank temperature, pressure, Dissolved oxygen concentration, mixed liquid suspension in the tank (MLSS),
Neural net optimizer (13), which calculates the target value of the dissolved oxygen concentration based on the data of the mixed liquid volatile suspended solid (MLVSS) in the tank, the measurement result of the dissolved oxygen concentration meter and the neural net optimizer PID control device with short-term prediction function (11) for calculating the amount of oxygen to be supplied based on the dissolved oxygen concentration also calculated based on the target value, the measurement result of the oxygen supply amount measuring device, and the PID control with the prediction function 3 shows a dissolved oxygen concentration control device for an aeration tank comprising an oxygen supply amount controller for adjusting an oxygen supply amount control valve based on an oxygen amount indicated by the device.

The method for controlling the dissolved oxygen concentration in an aeration tank using this control device incorporates the measurement result of a dissolved oxygen concentration meter (5) in the aeration tank into a PID control device (11) with a short-term prediction function, and In this way, the difference between the dissolved oxygen concentration and the target value calculated by the neural net optimizer is compared to calculate the oxygen supply amount that can be closer to the target dissolved oxygen concentration, and the result is used as the oxygen supply controller. (10) to control the oxygen supply amount by operating the oxygen supply amount control valve (9) in comparison with the measurement result of the oxygen supply amount measuring device (8), and subsequently to regulate the pressure of the aeration tank. The pressure control valve (7) is operated by the meter (12) to discharge the gas in the aeration tank (4) to a predetermined pressure.

[0022]

By using the control device of the present invention,
The dissolved oxygen concentration in the aeration tank can be predicted and controlled, and the dissolved oxygen concentration can be stabilized, so that the quality of the treated water can be stabilized. In addition, by combining the short-term prediction and the long-term prediction, not only the above-described dynamic control but also the cost-minimum control by the neural net optimizer can be simultaneously performed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a configuration of a control device for a dissolved oxygen concentration in an aeration tank according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Raw water flow meter 2 ... Raw water flow control valve 3 ... Return sludge flow meter 4 ... Aeration tank 5 ... Dissolved oxygen concentration meter 6 ... Pressure detector 7 ... Pressure regulation Valve 8 ... Oxygen supply amount measuring device 9 ... Oxygen supply amount control valve 10 ... Oxygen supply amount controller 11 ... PID controller with prediction function 12 ... Pressure control controller 13 ... Neural Net Optimizer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kazutoshi Itoyama 3-10 Utsudori, Kurashiki City, Okayama Prefecture Mitsubishi Chemical Mizushima Office (72) Inventor Yoshiaki Yamamoto 3-10 Utsudori, Kurashiki City, Okayama Prefecture Mitsubishi Chemical F-term in Mizushima Plant (reference) 4D028 AB00 BD07 CA07 CA10 CB01 CC00 CC01 CC05 CC07 CC12 CD01 CD08 CE03 4D029 AA09 AB05 BB10 CC02

Claims (5)

[Claims] 1. The dissolved oxygen concentration of an aeration tank (4) for wastewater treatment comprising an oxygen supply pipe, a raw water supply pipe, a return sludge receiving pipe, an exhaust pipe, and a discharge pipe to a settling tank for treated water and sludge. A control device comprising the following instrumentation device. a) Raw water flow meter (1) for measuring the flow rate of raw water supplied to the aeration tank and a raw water flow control valve (2) b) Return sludge flow meter (3) for measuring the sludge flow returned from the settling tank c) Dissolved oxygen concentration meter for measuring the dissolved oxygen concentration in the aeration tank (5) d) Pressure detector for measuring the internal pressure of the aeration tank (6) e) Installed in the exhaust pipe of the aeration tank to adjust the internal pressure of the aeration tank Pressure control valve (7) and pressure control controller (1
2) f) Oxygen supply amount control valve (9) for adjusting the amount of oxygen supplied to the aeration tank g) Oxygen supply amount measurement device (8) installed immediately near the oxygen supply amount control valve (9) in the oxygen supply pipe h) By inputting predetermined process data,
Neural net optimizer (1) that performs long-term prediction of dissolved oxygen concentration and calculates the target value of dissolved oxygen concentration
3) i) P with short-term prediction function for calculating the amount of oxygen to be supplied based on the measurement result of the dissolved oxygen concentration meter and the target value of the dissolved oxygen concentration calculated by the neural net optimizer
ID control device (11) j) Based on the measurement result of the oxygen supply amount measuring device (8) and the oxygen amount to be supplied indicated by the PID control device with short-term prediction function (11), the oxygen supply amount adjusting valve (9) Oxygen supply controller (10) 2. The dissolved oxygen in an aeration tank according to claim 1, wherein a discrete linear model taking into account dynamic characteristics of dissolved oxygen concentration with respect to the oxygen supply amount and noise is used as a prediction model of the PID control device with a short-term prediction function. Concentration control device. 3. Process data includes raw water temperature, flow rate, hydrogen ion concentration (pH), chemical oxygen demand (CO
D), Biochemical oxygen demand (BOD5), suspended solids (SS), aeration tank temperature, pressure, dissolved oxygen concentration, mixed liquid suspension in tank (MLSS), mixed liquid volatile suspension in tank The apparatus for controlling the concentration of dissolved oxygen in an aeration tank according to any one of claims 1 to 3, wherein at least one kind of data selected from the group consisting of substances (MLVSS) is used. 4. A method for controlling the concentration of dissolved oxygen in an aeration tank using the dissolved oxygen concentration control apparatus according to claim 1. 5. The method for controlling the concentration of dissolved oxygen in an aeration tank according to claim 3, wherein oxygen having a purity of 50% or more is used as the supplied oxygen.