JPH06254585A - Air blowing device for aeration tank - Google Patents

Abstract

PURPOSE:To prevent the degradation of a treatment capacity by controlling the rotating speed of an air blower by the signals from a dissolved oxygen sensor and a temp. sensor in such a manner that the saturation rate of the dissolved oxygen attains a target saturation rate at the time of driving this air blower and executing a sewage treatment by an activated sludge method. CONSTITUTION:This air blowing device for an aeration tank has the air blower 10 for supplying air via an air diffusion pipe 11 into the aeration tank 1 in which sewage is put. The air blower 10 is rationally driven by a universal three-phase AC motor 13 controlled in rotating speed by means of an inverter 14. The air blowing device is provided with the temp. sensor 15 for detecting the temp. of the sewage of the aeration tank 1, the dissolved oxygen sensor 16 for detecting the dissolved oxygen quantity in the sewage and a target saturation rate setting means 17 for setting the target saturation rate of the dissolved oxygen saturation rate of the dissolved oxygen of the sewage. The output signals therefrom are inputted to a control section 20. The actual saturation rate is calculated from the detected values of the satd. dissolved oxygen quantity and dissolved oxygen quantity based on the sewage temp. and the control value of the inverter 14 is set according to the deviation from the target saturation rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air blowing device for an aeration tank for treating sewage by a generally popular activated sludge method, and more particularly to a blower supplying air into the aeration tank. The present invention relates to an air blowing device for an aeration tank, which makes variable the amount of air blown by inverter control.

[0002]

2. Description of the Related Art Generally, wastewater treatment by the activated sludge method is performed in a tank called an aeration tank. In this tank, the aerobic microorganisms contained in the activated sludge are decomposing organic substances, and sufficient oxygen must be constantly supplied here. In general, supplying pure oxygen into this aeration tank increases the operating cost, and therefore a method of sending air by an air blowing device is generally used.

Conventionally, as an air blowing device of this type of aeration tank, for example, a device as shown in FIG. 9 is known (JP-A-53-122248). This is because the air is blown into the aeration tank 1 from the air blower 2 through the air diffuser 3 and a variable speed motor 4 is used to drive the air blower 2 and its rotation speed is changed, so that the amount of air blown from the air diffuser 3 is increased. The amount of dissolved oxygen is controlled within a certain range by controlling. That is, in this conventional air blowing device, the upper limit value and the lower limit value of the dissolved oxygen amount are set in advance, the dissolved oxygen amount in the aeration tank is detected by the DO sensor 5, and DO
The converter 6 converts the output value indicating the dissolved oxygen amount (hereinafter referred to as “DO meter value”). When the dissolved oxygen amount reaches the upper limit set value, the DO meter value and the set value of the upper limit setting unit match. As a result, the comparator 7 sends a deceleration signal to the variable speed motor 4 to slow down the rotation of the air blower 2 and reduce the aeration amount from the air diffuser 3. As a result, the dissolved oxygen amount begins to decrease and reaches the lower limit set value. On the other hand, when the DO meter value and the setting value of the lower limit setting unit match, the comparator 7 issues a speed increasing signal to the variable speed motor 4 to increase the rotation of the air blower 2,
The amount of aeration from the air diffuser 3 is increased. In this way
The amount of sewage supplied to the sewage treatment equipment and the concentration of organic substances contained in the sewage change from time to time by supplying air into the aeration tank to set the upper and lower limits of the dissolved oxygen amount in the aeration tank. It should be within the range of values.

In this way, the rotational speed of the motor is changed to control the dissolved oxygen amount within a certain range. When the air blower is operated continuously and continuously, most of the operating cost of the sewage treatment apparatus is the air blower. This is because it is occupied by the electricity charge and the operating cost increases. Also, if the amount of air corresponding to the maximum load is constantly supplied to the aeration tank, the turbidity of the discharged water deteriorates because the sludge in the tank is disassembled due to excessive aeration and the sludge is discharged without settling. .

[0005]

By the way, in the above-mentioned conventional air blowing device for the aeration tank, the rotational speed of the variable speed motor 4 is changed so that the dissolved oxygen amount is controlled within a certain range. However, since the upper and lower limits of the dissolved oxygen amount are given as set values for control, there is a range, and considering the change in the saturated dissolved oxygen amount due to the water temperature, the range is also set large. Therefore, there is a problem in that the operation time of the motor becomes longer and the amount of electric power is wasted.

Further, since the amount of dissolved oxygen in the aeration tank reciprocates between the upper limit value and the lower limit value, depending on these settings, the control system may become unstable and the processing capacity may decrease. Control responsiveness also deteriorates, and there is the problem that rapid changes in water quality in the aeration tank cannot be followed. Further, since the set value must be set to the upper limit value, the lower limit value, the deceleration amount and the acceleration amount for the motor, there is a problem that the setting operation becomes complicated.

The present invention has been made in view of the above problems, and it is possible to drive a blower motor with a target of a constant dissolved oxygen saturation rate regardless of a change in saturated dissolved oxygen amount due to water temperature, which is wasteful. This is to suppress the driving of the motor to further save the labor, and to keep the inside of the aeration tank at a constant saturation rate to stabilize the control system and prevent the deterioration of the processing capacity.

[0008]

The means of the present invention for solving such a problem is an air blower for supplying air to an aeration tank containing dirty water, a motor for driving the air blower, and a control. An inverter that changes the operating condition of the motor based on the value to control the amount of air blown into the air blower, a temperature sensor that detects the temperature of sewage in the aeration tank, and a dissolved oxygen sensor that detects the amount of dissolved oxygen in the sewage in the aeration tank. And a target saturation ratio setting means for setting a target saturation ratio of the dissolved oxygen saturation ratio of the sewage, and the inverter based on the detection result of the temperature sensor and the detection result of the dissolved oxygen sensor so that the target saturation ratio is set. And a control unit that determines the control value of.

Then, if necessary, the control unit includes a saturated dissolved oxygen amount calculating means for calculating the saturated dissolved oxygen amount in water at the temperature based on the detection result of the temperature sensor, the detection result of the dissolved oxygen sensor and the saturated dissolved oxygen amount. The actual saturation rate calculating means for calculating the actual saturation rate of the dissolved oxygen saturation rate from the calculation result of the amount calculating means, the target saturation rate set in the target saturation rate setting means and the actual saturation rate calculated by the actual saturation rate calculating means. And a control value determining means for determining the control value of the inverter so that the actual saturation rate matches the target saturation rate based on the comparison result of the comparing means.

Further, if necessary, the control unit is
From the saturated dissolved oxygen amount calculating means for calculating the saturated dissolved oxygen amount in water from the detection result of the temperature sensor, and the saturated dissolved oxygen amount calculated by the saturated dissolved oxygen amount calculating means and the target saturation rate set in the target saturation rate setting means. A comparison comparing the target oxygen amount calculating means for calculating the target oxygen amount of the dissolved oxygen amount at the temperature, and the target oxygen amount calculated by the target oxygen amount calculating means and the actual oxygen amount of the dissolved oxygen amount detected by the dissolved oxygen sensor. And a control value determining unit that determines the control value of the inverter so that the actual oxygen amount matches the target oxygen amount based on the comparison result of the comparing unit.

When the air from the air blower is branched from the path leading to the aeration tank and used for another purpose, the control unit controls the rotation speed of the air blower regardless of the determined control value. It is effective to have other-use control value giving means for giving the inverter another control value to operate at the designed value.

Further, when the stop time of the air blower exceeds a certain time, the control section gives the inverter another control value for forcibly operating the air blower regardless of the determined control value. It is effective to have the forced operation control value giving means.

Further, it is effective that the control section is provided with a display means for displaying the actual saturation rate or the actual oxygen amount and the control value of the inverter.

[0014]

According to the air blowing device of the aeration tank configured as described above, the air blower can be driven by setting the target saturation rate of the dissolved oxygen saturation rate of sewage in the target saturation rate setting means in advance. When the sewage treatment by the activated sludge method is performed, the air blower is adjusted so that the dissolved oxygen saturation rate in the aeration tank reaches the set target saturation rate by the signals from the dissolved oxygen sensor and temperature sensor installed in the aeration tank. Is controlled by an inverter to adjust the amount of air discharged to the aeration tank.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An air blowing device for an aeration tank according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings.
As shown in FIG. 1, in the air blowing device for an aeration tank according to the embodiment, 10 is an air blower for supplying air to the aeration tank 1 in which dirty water is put, and 11 is an aeration tank for air supplied from the air blower 10. It is an air diffuser that blows into the inside of 1. The air path from the air blower 10 to the air diffuser 11 is branched, and this branch path 12 is used for another purpose, in the embodiment, when the sludge returning device for returning sludge is used every predetermined time. .

Reference numeral 13 is a general-purpose three-phase AC motor for driving the air blower 10. The lower limit value of the rotation speed is set to 20% of the rated frequency regardless of the output wattage of the air blower 10 due to its characteristics. 14 is the motor 1 based on the control value
3 is an inverter that controls the amount of air blown into the air blower 10 by changing the operating conditions of No. 3. The inverter 14 drives the motor 13 at a frequency corresponding to an analog signal as a control value sent from the control unit 20 described later. Further, the inverter 14 receives the stop signal and the operation signal as the control value sent from the control unit 20 described later, and the motor 1
Stop and run 3. Furthermore, the lower limit value of the operating frequency to the general-purpose inverter 14 is set to 20% on the control algorithm of the air blowing device of the aeration tank 1.

Further, in the air blowing device, 15 is a temperature sensor for detecting the temperature of the sewage in the aeration tank 1, and 16 is a dissolved oxygen sensor for detecting the amount of dissolved oxygen in the sewage in the aeration tank 1. As the dissolved oxygen sensor 16, for example, a well-known diaphragm type galvanic cell type or a diaphragm type polarographic type is used. Further, 17 is a target saturation rate setting means for setting a target saturation rate M of the dissolved oxygen saturation rate of sewage.

A control unit 20 determines the control value of the inverter 14 based on the detection result of the temperature sensor 15 and the detection result of the dissolved oxygen sensor 16 so that the dissolved oxygen saturation rate is set. Is. More specifically, as shown in FIG. 2, the control unit 20 includes a saturated dissolved oxygen amount calculation means 21 that calculates the saturated dissolved oxygen amount in water at the temperature based on the detection result of the temperature sensor 15. As shown in FIG. 4, the saturated dissolved oxygen amount calculating means 21 calculates the saturated dissolved oxygen amount at the detection temperature from the relationship line between the water temperature and the saturated dissolved oxygen amount in water.

The control unit 20 also includes a dissolved oxygen sensor 16
The actual saturation rate calculating means 22 for calculating the actual saturation rate S of the dissolved oxygen saturation rate from the detection result of the above and the calculation result of the saturated dissolved oxygen amount calculating means 21, and the target saturation rate M set in the target saturation rate setting means 17. A comparison means 23 for comparing the actual saturation rate S calculated by the actual saturation rate calculation means 22, and a comparison means 23.
And a control value determining means 24 that determines the control value of the inverter 14 so that the actual saturation rate S matches the target saturation rate M based on the comparison result.

Further, when the air from the air blower 10 is branched from the path leading to the aeration tank 1 and used in the sludge returning device, the control section 20 receives the sludge returning operation signal and the control value determined above. Irrespective of the above, other control values for operating the rotation speed of the air blower 10 at the designed value are set to the inverter 1
4 is provided with another use control value giving means 25.

Furthermore, the control unit 20 controls another control value for forcibly operating the air blower 10 regardless of the determined control value when the stop time of the air blower 10 exceeds a certain time. Is provided to the inverter 14. 27 is a display means for displaying the actual saturation rate and the control value of the inverter.

The function of the control unit 20 is realized by the microcomputer system shown in FIG. In FIG. 3, 34a and 34b are A / D converters which respectively convert two analog signals from the temperature sensor 15 and the dissolved oxygen sensor 16 into digital quantities, 32 is a RAM which stores the converted digital quantities, and 33 is a dissolved quantity. The setting switch 33 is the target saturation rate setting means 17 for setting the target saturation rate M of the oxygen saturation rate. 32 is ROM3
An actual saturation rate S of the dissolved oxygen saturation rate, which is an MPU operated by a program stored in 0, in which the two digital quantities are digitally filtered in order to remove the influence of noise and then the temperature is corrected by calculation. Converted to
The actual saturation rate S corrected for temperature and the target saturation rate M are compared,
From this result, the control value for the general-purpose inverter 14 is obtained by digital PID calculation. In this case, the control value is the number of revolutions of the motor 13 displayed in percentage. Reference numeral 39 is an I / O port for exchanging signals.

Reference numeral 37 denotes a D / A which converts a control value for the inverter 14 into an analog signal and outputs it to the inverter 14.
It is a converter. From the comparison result of the actual saturation rate S and the target saturation rate M, reference numeral 38 sends a stop signal to the inverter 14 to stop the operation of the air blower 10 when the dissolved oxygen is more than sufficient, and the dissolved oxygen saturation rate decreases. This is a relay that sends an operation signal to the inverter 14 and restarts the operation of the air blower 10 when the above operation is performed.

Reference numeral 36 is a temperature-corrected dissolved oxygen saturation rate, water temperature, a control value for the inverter 14, a liquid crystal display as a display means for displaying the actual saturation rate S, and 35 is the sludge return operation signal. This is the input switch.

Therefore, in the air blowing device for the aeration tank 1 according to this embodiment, the target saturation ratio M of the dissolved oxygen saturation ratio is set in the target value setting switch 33 in advance. In this case, since only the switch operation is required, the upper and lower limits of the dissolved oxygen amount, the deceleration amount to the motor, and
The operability becomes extremely good without the complexity of giving the four acceleration values as set values for control.

When the apparatus is in operation, as shown in FIG. 5, the control unit 20 controls the dissolved oxygen sensor 16 to move to the aeration tank 11.
Receives the amount of dissolved oxygen in sewage as an analog signal. Further, the temperature of the sewage water is received as an analog signal from the temperature sensor 15.

In the control unit 20, all operations are performed in the ROM 30.
This is performed by the MPU 32 operating according to the program stored in. The above two analog signals are converted into digital quantities by the A / D converters 34a and 34b, respectively, and stored in the RAM 32. These two digital quantities are converted into an actual saturation rate S of the dissolved oxygen saturation rate in which the temperature has been corrected by calculation after being subjected to digital filtering in order to remove the influence of noise.

On the other hand, when the value of the target saturation rate M of the dissolved oxygen saturation rate set by the setting switch 33 is read, the temperature-corrected actual saturation rate S and the target saturation rate M are compared, and the inverter 14 is calculated by the digital PID calculation. A control value is required. The control value for this inverter 14 is D /
The analog signal is converted by the A converter 37 into the inverter 14
Is output to. The inverter 14 drives the motor 13 at a frequency according to the input analog signal. As a result, the air blower 10 rotates and air is supplied to the aeration tank 1 by the air diffuser 11.

Further, according to the above comparison result, when the dissolved oxygen is more than sufficient, the relay 38 operates to send a stop signal to the inverter 14 to stop the operation of the air blower 10. Further, according to the above comparison result, when the dissolved oxygen saturation rate decreases, the relay 38 operates, an operation signal is sent to the inverter 14, and the operation of the air blower 10 is restarted.

In this case, even if there is a day-night temperature change or a summer-winter temperature change, in this embodiment, the microcomputer calculates in accordance with the change in the water temperature, so that a constant target value that is a set value is obtained at any water temperature. Since the inverter 14 controls the rotation speed of the motor 13 with the saturation rate M (%) as the target, unlike the conventional case where a constant value (mg / l) is targeted, when the water temperature rises, the target value is eventually set. Since the value (mg / l) to be reduced decreases, the number of revolutions can be reduced by that amount, and the amount of electric power can be saved. In particular, since the target saturation rate M does not change even if the saturated dissolved oxygen amount changes due to temperature change, when the respiration rate of aerobic microorganisms is small, such as when the temperature is low in winter, the power consumption of the motor 13 is significantly reduced. Is reduced to.

Regarding the power saving of the operation of the air blower 10,
The following results were obtained in the demonstration operation. Air blower 10 per day (rated power 2.2kWh)
Average power consumption of 1. Without control 40.5kWh / day 2. In the case of control according to the example: 31.2 kWh / day

Further, in this case, a control value for the inverter 14 is obtained by a digital PID control calculation by software, and this is converted into a control signal to convert the inverter 1 into a control signal.
Since it is sent to No. 4, finer and stepless adjustment can be performed, and control with less fluctuation and response delay becomes possible.
Further, since the inside of the aeration tank 1 is always maintained at a constant saturation rate, the control system is stabilized and the decrease in processing capacity is prevented.

Furthermore, since the motor 13 is the three-phase AC motor 13, it is less expensive than the expensive variable motor 13. When the air blower 10 is driven by the general-purpose three-phase AC motor 13, the lower limit value of the rotation speed is 20% of the rated frequency regardless of the output wattage of the air blower 10 due to its characteristics.
Is. Below this, abnormal vibration called surging occurs and normal operation cannot be performed. Since the lower limit value of the operating frequency to the inverter 14 is set to 20% in the control algorithm of the air blowing device of the aeration tank 1, this prevents surging.

If the operating frequency of the inverter 14 at the upper limit of the discharge pressure is set as the upper limit value of the frequency and the operating frequency of the inverter 14 at the lower limit of the discharge pressure is set as the lower limit value, the discharge pressure can be designed at the time of designing the sewage treatment apparatus. The range can be adjusted. These settings are stored in the inverter 14 once set at the time of installation of the apparatus and are not lost even when the power of the inverter 14 is turned off.

Further, the air blower 1 is continuously operated for a certain time or longer.
When 0 is stopped, the air blower 10 is operated regardless of the dissolved oxygen saturation rate. When the air blower 10 is stopped, the sludge settling in the aeration tank 1 starts, which prevents the sludge settling due to a long stoppage.

When the sludge return operation signal is input, the input switch 35 operates and the rotation speed signal and the operation signal are output to the inverter 14 so that the inverter 14 operates at the designed rotation speed regardless of the dissolved oxygen saturation rate. It Therefore, deterioration of purified water quality due to a decrease in the amount of aerated air is prevented.

FIGS. 6 and 7 show the dissolved oxygen saturation ratio in the aeration tank 1 when the air blower 10 is continuously operated without control and when the air blower 10 is controlled according to this embodiment. It is the graph which showed each experimental value. According to this, it can be seen that the target constant dissolved oxygen saturation rate is obtained by the present embodiment, and it can be said that the dissolved oxygen is not insufficient even if the air blower 10 is controlled.

As shown in FIG. 8, reference numeral 40 shows another example of the configuration of the control unit. The control unit 40 according to this example calculates the saturated dissolved oxygen amount in water from the detection result of the temperature sensor 15, and the same saturated dissolved oxygen amount calculating unit 41 as described above, and the saturated dissolved oxygen amount calculating unit 41 calculates the saturated dissolved oxygen amount. A target oxygen amount calculating means 42 for calculating a target oxygen amount N of the dissolved oxygen amount at the temperature from the oxygen amount and the target saturation rate M set in the target saturation rate setting means 17, and a target calculated by the target oxygen amount calculating means 42. Comparing means 43 for comparing the oxygen amount N with the actual oxygen amount T of the dissolved oxygen amount detected by the dissolved oxygen sensor 16;
The control value determining means 44 determines the control value of the inverter 14 so that the actual oxygen amount T matches the target oxygen amount N based on the comparison result of the comparing means 43. Reference numeral 47 is a display means for displaying the actual oxygen amount T and the control value of the inverter.

The control unit 40 also controls the inverter 14 for the rotation speed of the motor 13 with the target oxygen amount N calculated from the constant target saturation rate M (%) which is a set value at any water temperature as a target. Similarly, the power consumption can be saved.

In the above embodiment, the target saturation rate may be set in any way.

[0041]

As described above, according to the air blowing device for the aeration tank of the present invention, the number of revolutions of the motor is controlled by the inverter targeting the constant dissolved oxygen saturation rate which is the set value at any water temperature. Therefore, unlike the conventional case where a fixed amount of dissolved oxygen is set as the target, when the water temperature rises, the target amount of dissolved oxygen decreases as a result, so the rotation speed can be reduced by that amount. Therefore, it is possible to suppress unnecessary driving of the motor and further save the labor.

Further, since the inside of the aeration tank can always be maintained at a constant saturation rate, the control system can be stabilized and the deterioration of the processing capacity can be prevented. Therefore, it is possible to prevent the water quality of the discharged water from deteriorating due to sludge dismantling due to excessive aeration, and to stabilize the water quality of the discharged water by controlling the fluctuation of the dissolved oxygen amount and reducing the response delay. Furthermore, since it is sufficient to set only the target saturation rate as the set value, there is an effect that the setting operation becomes easy.

When the other-use control value giving means is provided, it is possible to prevent the quality of purified water from being deteriorated due to the decrease of the aeration air amount due to the other use.

Further, when the forced operation control value giving means is provided, there is an effect that the sludge can be prevented from settling due to a long stop.

Further, when the display means for displaying the actual saturation rate or the actual oxygen amount and the control value of the inverter is provided, the situation with respect to the target can be visually recognized and the operating state of the apparatus can be grasped. The effect is that you can do it.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an air blowing device for an aeration tank according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a control unit of the air blowing device for the aeration tank according to the embodiment of the present invention.

FIG. 3 is a diagram showing a specific configuration of an air blowing device for an aeration tank according to an embodiment of the present invention.

FIG. 4 is a graph showing the amount of saturated dissolved oxygen in water as a function of water temperature.

FIG. 5 is a flowchart showing the operation of the air blowing device for the aeration tank according to the embodiment of the present invention.

FIG. 6 is a graph of the dissolved oxygen saturation rate in the aeration tank when the air blower is not controlled.

FIG. 7 is a graph of the dissolved oxygen saturation rate in the aeration tank when controlled according to this example.

FIG. 8 is a block diagram showing the configuration of another control unit of the air blowing device for the aeration tank according to the embodiment of the present invention.

FIG. 9 is a diagram showing an example of a conventional air blowing device for an aeration tank.

[Explanation of symbols]

 1 aeration tank 10 air blower 13 motor 14 inverter 15 temperature sensor 16 dissolved oxygen sensor 17 target saturation rate setting means 20 control unit M target saturation rate S actual saturation rate 21 saturated dissolved oxygen amount calculation means 22 actual saturation rate calculation means 23 comparison means 24 Control Value Determining Means 25 Other Use Control Value Applying Means 26 Forced Operation Control Value Applying Means 27 Displaying Means 40 Control Unit T Actual Oxygen Amount N Target Oxygen Amount 41 Saturated Dissolved Oxygen Amount Calculating Means 42 Target Oxygen Amount Calculating Means 43 Comparing Means 44 Control value determination means 47 Display means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Kayaba No.11, Nishimiyanome, Hanamaki-shi, Iwate Prefecture No. 1 11th percentile S-Brain Toyouchi Co., Ltd.

Claims (6)

[Claims] 1. An air blower for supplying air to an aeration tank containing dirty water, and a motor for driving the air blower,
An inverter that changes the operating conditions of the motor based on the control value to control the amount of air blown into the air blower, a temperature sensor that detects the temperature of sewage in the aeration tank, and dissolved oxygen that detects the amount of dissolved oxygen in the sewage of the aeration tank. A sensor, a target saturation rate setting means for setting a target saturation rate of the dissolved oxygen saturation rate of sewage, and the above-mentioned based on the detection result of the temperature sensor and the detection result of the dissolved oxygen sensor so as to reach the set target saturation rate An air blowing device for an aeration tank, comprising: a control unit that determines a control value of an inverter. 2. The controller comprises a saturated dissolved oxygen amount calculating means for calculating a saturated dissolved oxygen amount in water at the temperature based on a detection result of the temperature sensor, and a detection result of the dissolved oxygen sensor and a saturated dissolved oxygen amount calculating means. Comparison comparing the actual saturation rate of the dissolved oxygen saturation rate from the calculation result with the actual saturation rate calculation means and the target saturation rate set in the target saturation rate setting means and the actual saturation rate calculated by the actual saturation rate calculation means Means and
2. An air blower for an aeration tank according to claim 1, further comprising control value determining means for determining the control value of the inverter so that the actual saturation rate matches the target saturation rate based on the comparison result of the comparing means. Including device. 3. The control unit includes a saturated dissolved oxygen amount calculating means for calculating a saturated dissolved oxygen amount in water from a detection result of a temperature sensor, and a saturated dissolved oxygen amount and a target saturation rate calculated by the saturated dissolved oxygen amount calculating means. Target oxygen amount calculating means for calculating the target oxygen amount of the dissolved oxygen amount at the temperature from the target saturation ratio set in the setting means, the target oxygen amount calculated by the target oxygen amount calculating means and the dissolved oxygen detected by the dissolved oxygen sensor And a control value determining means for determining the control value of the inverter so that the actual oxygen amount matches the target oxygen amount based on the comparison result of the comparing means. An air blowing device for an aeration tank according to claim 1. 4. When the air from the air blower is branched from the path leading to the aeration tank and used for another purpose, the control unit controls the rotation speed of the air blower regardless of the determined control value. An air blowing device for an aeration tank according to claim 1, 2 or 3, further comprising: another use control value giving means for giving the inverter another control value to operate at the designed value. 5. The control unit provides the inverter with another control value for forcibly operating the air blower regardless of the determined control value when the stop time of the air blower exceeds a certain time. The air blowing device for an aeration tank according to claim 1, 2, 3 or 4, further comprising a forced operation control value giving means. 6. The control unit comprises display means for displaying the actual saturation rate or the actual oxygen amount and the control value of the inverter, 2, 3, 4 or 5.
Air blowing device for the aeration tank described.