JPH09141289A - Operation control method for oxidation ditch system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an operation control method capable of improving the quality of a treated water by optimally setting control factors such as the time ratio of aeration to stoppage of a mechanical aeration agitator in an oxidation-ditch system, being is one of sewerage disposal methods. SOLUTION: A respiration speed meter 10 is provided at the downstream side of a raw water flow-in port 2 and the aeration and the stoppage of aeration of the mechanical aeration agitator 3 is controlled based on the measured value by a controller 11. Also the respiration speed mater 10 and a dissolved oxygen meter 13 are provided respectively at the upstream side and the downstream side of the mechanical aeration agitator 3 and the supply quantity of oxygen by the mechanical aeration agitator 3 is controlled based on the measured value of the respiration speed meter 10, and the aeration and the stoppage of aeration of the mechanical aeration agitator 13 are controlled by estimating a position where the dissolved oxygen concentration DO becomes 0 based on each measured value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling operation by using a respiration rate meter in an oxidation ditch method (hereinafter abbreviated as OD method) which is one of sewage treatment methods.

[0002]

2. Description of the Related Art With the recent improvement of sewerage, research on treatment methods at small-scale sewage treatment plants is progressing. Above all, the system configuration is simple, construction cost and maintenance cost are low, and treated water quality is low. The OD method, which is stable, is drawing attention. This OD method is a type of activated sludge method. As shown in FIG. 6, raw water 2 is introduced into an elliptic biological reaction tank 1 which is an endless water channel having an appropriate water depth, and partition walls 4 are used. A circulation flow is created by using a mechanical aeration stirrer 3 such as a rotor to mix the raw water with the activated sludge while circulating the raw water as shown by the arrow A to supply oxygen necessary for the treatment.

Reference numeral 5 is a final sedimentation pond, and this final sedimentation pond 5
The supernatant liquid is discharged as treated water 6 through a disinfecting tank (not shown), etc., and a part of the sludge settled in the final settling tank 5 is returned to the biological reaction tank 1 via a pipe 7. And excess sludge 8
Is sent to a surplus sludge treatment device (not shown) for treatment.
1 or 2 mechanical aeration mixers per bioreactor
It is customary to use four or four units.

In this OD method, the hydraulic retention time (HRT) of the inflowing raw water 2 is set to be longer than that of the standard activated sludge method, and the activated sludge suspended matter (MLSS) is increased so that the volume load is increased. It has the characteristic that both sludge load is low. Therefore, it has the advantages that it is resistant to fluctuations in inflow load and that the amount of sludge generated is small, and because it is relatively easy to maintain and manage, the number of small-scale sewage treatment plants is increasing.

On the other hand, in order to prevent eutrophication in a closed water area, it is required to reduce nitrogen and phosphorus in raw water during sewage treatment. Nitrogen removal in the OD method can be performed by providing a concentration gradient of dissolved oxygen (DO) in the flow direction in the endless water channel to partially create an anaerobic / aerobic state and causing a denitrification / nitrification reaction. However, in this case, it is important to keep the mixing state of sludge uniform while maintaining the DO concentration gradient in the biological reaction tank 1.

[0006]

The above-mentioned OD method is basically set to be carried out at low load operation, but the load is generally smaller at the beginning of operation. It is known that it takes a considerable amount of time to reach the planned water volume. When the stirring operation is continuously performed as described above, the dissolved oxygen concentration (hereinafter abbreviated as DO concentration) increases, and there is a problem that a so-called over-aeration state is likely to occur.

[0007] In the over-aeration state, sludge is dispersed, and the sedimentation separability of sludge in the final settling basin 5 is deteriorated, which may deteriorate the quality of treated water. Further, since the DO concentration becomes higher as a whole, the denitrification reaction that requires an anaerobic state is less likely to occur, so that the nitrogen removal rate also decreases.

[0008] In response to the above, means for carrying out intermittent aeration by stopping the stirring operation by the agitator at a certain time is also known, but such intermittent aeration means is
Since the processing efficiency varies depending on the setting of the aeration / stopping time ratio or the total time of one cycle, there is a problem that it is technically difficult to optimally set the time ratio and the total time.

Further, in the case of continuously operating with the inflow of raw water close to the planned amount of water secured, a method of adjusting the DO concentration distribution by changing the operating number of aeration agitators or the agitation rotation number is used, but the load It is difficult to optimally adjust the above factors in consideration of the effects of fluctuations and changes in water temperature due to seasonal changes. For example, when the load is low, the DO concentration becomes high, so that the anaerobic portion becomes small, and in some cases, the entire reaction tank may become aerobic. In such a case, there is a fear that the nitrogen removing effect will be extremely lowered.

On the other hand, when the load is high, the anaerobic portion increases, the nitrification reaction that occurs in the aerobic state is stopped, and as a result, the nitrogen removal rate may decrease. The reality is that no method has been developed for optimally controlling this anaerobic and aerobic part.

Therefore, the present invention has been made in view of the above, and optimally sets a control factor such as a time ratio of aeration and stop of a mechanical aeration stirrer to prevent excessive aeration and to separate sludge sedimentation. It is an object of the present invention to provide an operation control method capable of improving the quality of treated water by improving the quality of the treated water and preventing the decrease in the nitrogen removal rate due to the increase in the DO concentration.

[0012]

[Means for Solving the Problems] In order to achieve the above object, the present invention allows raw water to flow into a bioreaction tank consisting of a non-terminating water channel to perform aeration by a mechanical aeration stirrer installed in the channel. In the water treatment apparatus by the oxidation-ditch method, in which the raw water is circulated and mixed with the activated sludge, first, according to claim 1, a respiration rate meter is installed on the downstream side of the raw water inlet, There is provided an operation control method in which a control device drives and controls aeration and an aeration stop state of a mechanical aeration stirrer based on a measurement value of a speedometer.

According to claim 2, a respiration rate meter is installed on the upstream side of the mechanical aeration stirrer, and a dissolved oxygen concentration meter is installed on the downstream side of the mechanical aeration stirrer. When the value is high, control is performed to increase the oxygen supply by the mechanical aeration stirrer, while when the measured value of the respiration rate meter is low, control is performed to reduce the oxygen supply to measure the dissolved oxygen concentration. The position where the dissolved oxygen concentration becomes zero is predicted from the value and the respiration rate value, and the aeration and aeration stop state of the mechanical aeration mixer are drive-controlled.

Further, according to claim 3, a plurality of mechanical aeration stirrers and a respiration rate meter are installed in the biological reaction tank, and a plurality of machines are controlled by the controller based on the measured value of the respiration rate meter. Provided is an operation control method in an oxidation ditch method in which the aeration and aeration stop states of a static aeration stirrer are individually driven and controlled.

According to the operation control method of the first aspect, when the influent pollutant concentration is high and the respiration rate of microorganisms is also high, the control device controls the aeration by the mechanical aeration mixer based on the measured respiration rate. When the time setting is made longer and conversely the inflowing pollutant concentration is low, control is performed such that the aeration time by the mechanical aeration stirrer is shortened or the stirrer is stopped for a long time.

According to the operation control method of the second aspect, in addition to the above action, the dissolved oxygen concentration is measured by the dissolved oxygen concentration meter, and the position where DO becomes zero is calculated from the DO value and the respiration rate value. By changing the number of rotations of the mechanical aeration agitator by these measured values and calculated values,
The aerobic time and range are optimally determined.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Various embodiments of an operation control method in an oxidation / ditch method according to the present invention will be described below with reference to the drawings, in which the same components as those of the conventional example are designated by the same reference numerals. To do. FIG. 1 is a schematic view of a main part showing a first embodiment of the present invention, in which raw water 2 is introduced into an elliptical biological reaction tank 1 formed of an endless water channel having an appropriate water depth as described above, The mechanical aeration stirrer 3 such as a rotor is rotated by the driving force of the drive motor 3a to create a circulating flow of raw water shown by an arrow A. Then, the raw water 2 is mixed with the activated sludge and the mechanical aeration stirrer 3 supplies oxygen necessary for the treatment. Reference numeral 4 is a partition wall for defining an endless water channel. Reference numeral 9 is a sludge returned from the sludge settled in the final settling tank (not shown) to the biological reaction tank 1.

In the first embodiment, a respiration rate meter (abbreviated as Rr meter) 10 is installed slightly downstream of the inlet of the raw water 2, and the measured value of the respiration rate meter 10 is the control device 11. Has been entered in. Then, the drive state of the mechanical aeration stirrer 3 is controlled by the control output 11a of the control device 11. Here, the number of mechanical aeration stirrers 3 is not limited to one, and several may be installed as needed.

According to the first embodiment, during the normal operation, the raw water 2 flows in the direction shown by the arrow A with the aeration action (aeration) due to the intermittent rotation of the mechanical aeration stirrer 3 and flows in the biological reaction tank 1. The reaction proceeds by mixing with activated sludge while circulating along the partition walls 4. Effluent 1 after reaction
2 is sent to the final sedimentation pond outside the figure.

When the concentration of pollutants in the raw water 2 is high, the respiration rate Rr of the microorganisms is also high, so that the rate of increase of the DO concentration is slow after the start of aeration, and the time required for the oxidative decomposition of the substrate is long. To become. Therefore, the respiration rate Rr of the microorganism is measured by the respiration rate meter 10, and the obtained measurement value is input to the control device 11. Then, by controlling the drive motor 3a by the control output 11a of the control device 11, control is performed to lengthen the aeration time set by the mechanical aeration stirrer 3.

On the contrary, when the concentration of the inflowing pollutant is low, the respiration rate Rr of the microorganisms is also low, so that the DO after the aeration is stopped.
The time required for lowering the concentration becomes longer and the anaerobic time for the denitrification reaction becomes shorter. In such a case, respiration rate meter 1
Based on the respiration rate Rr of the microorganism measured by 0,
Similarly, the drive output of the drive motor 3a is controlled by the control output 11a of the control device 11 to shorten the aeration time of the mechanical aeration stirrer 3 and extend the stop time of the stirrer.

By performing such control, it is possible to detect the load fluctuation due to the inflowing pollutant concentration by the measurement value of the respiration rate meter 10 and optimally control the aeration time and the stop time in the intermittent operation.

The measurement principle of the respiration rate meter 10 will be briefly described. Normally, the respiration rate of activated sludge is used as an evaluation of activity. The operation principle of this respiration rate meter is that dissolved oxygen (DO) in sample water is used. It is customary to calculate from the decay rate of). Specifically, when the sample water is introduced into the measuring tank, the activated sludge is aerated to increase the DO concentration, and then the aeration is stopped and stirring is performed, the DO concentration is increased due to the oxygen consumption by the aerobic microorganisms of the activated sludge. Will decrease, so change this to D
The respiration rate of the activated sludge is calculated by the least squares method from the reduction rate of DO measured by the O meter.

Next, a second embodiment of the present invention will be described with reference to FIG. The basic structure of the second embodiment is similar to that of the first embodiment, and is designated by the same reference numeral. In this example, the respiration rate meter 10 is installed on the upstream side of the mechanical aeration stirrer 3, and the dissolved oxygen concentration meter 13 (DO meter) is installed on the downstream side of the mechanical aeration stirrer 3.

In the second embodiment, since the measured value of the respiration rate meter 10 becomes high when the inflowing pollutant concentration is high,
The drive motor 3a is controlled by the control output 11a of the controller 11.
When the respiration rate meter 10 has a low measurement value, the rotation speed of the drive motor 3a is decreased to avoid unnecessary oxygen supply. Control is performed to reduce the oxygen supply. Further D
The dissolved oxygen concentration is measured by the O meter 13, and the position at which DO becomes zero is calculated from the DO value and the Rr value.

By changing the number of revolutions of the mechanical aeration stirrer 3 based on these measured values and calculated values, it is possible to optimally determine the time of the aerobic state or the range of the aerobic portion.

Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment is an example in which two mechanical aeration stirrers are installed, and the first mechanical aeration stirrer 14 and the drive motor 3b are installed on the downstream side of the inflow port of the raw water 2. On the downstream side of the eye mechanical aeration stirrer 14, a respiration rate meter 10 similar to that of the above embodiment, a second mechanical aeration stirrer 3 and a drive motor 3a are installed. The drive motor 3b attached to the first mechanical aeration stirrer 14 is constantly rotating at a preset fixed speed.

In this embodiment, the load fluctuation caused by the inflowing pollutant concentration is detected by the measurement value of the respiration rate meter 10, and the aeration time and the stop time of the mechanical aeration stirrer 3 by the drive motor 3a in the intermittent operation are controlled. Only carry out.
When the drive motor 3a has a variable speed, the rotation speed is controlled, and when the drive motor 3a rotates at a fixed speed, the on / off control is performed.

Since the inflow pollutant concentration is decomposed by activated sludge using oxygen supplied from the aerators 3 and 14, the pollutant concentration becomes lower toward the downstream side. Therefore, if the decomposition into pollutants is completed at the position where the Rr meter 10 shown in FIG.
The measured value of is the consumption rate of only internal respiration, and if the decomposition is not completed, it becomes the consumption rate to which the value required for decomposition of pollutants is added.

Therefore, when it is determined from the measured Rr value that the state is the internal respiration state, the drive of the mechanical aeration agitator 3 which is the second aerator from the inlet of the raw water 2 is stopped. Alternatively, the operation may be performed by lowering the rotation speed to the minimum. On the contrary, if the decomposition is not completed, the drive of the mechanical aeration stirrer 3 is continued or the operation is performed by increasing the rotation speed. Carry out.

FIG. 4 is a schematic view of an essential part showing a fourth embodiment of the present invention. In this example, in two mechanical aeration mixers installed, 1 from the inlet of raw water 2 toward the inflow direction The drive motor 3b of the second mechanical aeration stirrer 14 is set to a variable speed, and 2
The drive motor 3a of the third mechanical aeration mixer 3 is rotating at a preset fixed speed. The Rr meter 10 is installed on the upstream side of the second mechanical aeration stirrer 3. Therefore, the control output 11a of the control device 11 is input to the drive motor 3b of the first mechanical aeration mixer 14.

In the fourth embodiment, the evaluation of the measurement value of the Rr meter 10 is the same as that in the third embodiment, and when the Rr value is judged to be the internal respiratory state, the flow rate of the raw water 2 is increased. The drive of the mechanical aeration stirrer 14 which is the first aerator from the inlet may be stopped or the operation may be performed with the number of rotations lowered to the minimum. Control is performed such that the aeration stirrer 14 is continuously driven or the rotation speed is increased to perform the operation.

FIG. 5 is a schematic view showing a fifth embodiment of the present invention. In this embodiment, both drive motors 3a and 3b of the mechanical aeration stirrers 3 and 14 installed in the fourth embodiment can be used. This is an example of gear shifting, and the control output 11 of the control device 11
a is input to the drive motors 3a and 3b of both mechanical aeration mixers.

In the fifth embodiment, when it is determined that the Rr value is the internal respiratory state, first, the raw water 2
Mechanical aeration stirrer 3 which is the second aerator from the inlet of
If you stop the drive of or drive with the rotation speed reduced to the minimum and still have an internal respiratory condition,
The drive of the mechanical aeration stirrer 14 which is the first aerator is stopped or operation is performed with the rotation speed reduced. On the contrary, if the decomposition is not completed, the rotation speed of the first mechanical aeration stirrer 14 is increased, and if the internal respiratory state is still not reached, the rotation speed of the second mechanical aeration stirrer 3 is increased. The control is carried out by raising the speed of operation.

[0035]

As described in detail above, according to the operation control method in the oxidation / ditch method according to the present invention, the following operational effects are brought about. That is, when the pollutant concentration of raw water is high and the respiration rate of microorganisms is also high, the aeration time is set longer by the mechanical aeration agitator based on the measured respiration rate. In this case, by performing control such that the aeration time is shortened or the stop time is lengthened, it is possible to prevent over-aeration based on the continuous stirring operation and enhance the sludge sedimentation separability.

According to the operation control method of the second aspect, in addition to the above effects, the position where DO becomes zero is calculated from the DO value and the respiration rate value measured by the dissolved oxygen concentration meter, and these values are calculated. By changing the rotation speed of the mechanical aeration stirrer based on the measured value and the calculated value, the time and range of the aerobic condition can be optimally determined.

Therefore, according to the present invention, there is no decrease in the nitrogen removal rate due to an increase in the DO concentration as a whole, and a mechanical aeration stirrer is used even when continuous operation is performed with an inflow of raw water close to the planned amount of water being secured. Since it is possible to optimally set the control factors such as the time ratio of the aeration and the stoppage, the nitrogen removal rate is prevented from lowering due to the increase of the DO concentration and the treated water quality is improved together with the prevention of the over-aeration. It is possible to provide an operation control method capable of performing the operation control.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part showing a first embodiment of the present invention.

FIG. 2 is a schematic view of a main part showing a second embodiment of the present invention.

FIG. 3 is a schematic view of a main part showing a third embodiment of the present invention.

FIG. 4 is a schematic view of a main part showing a fourth embodiment of the present invention.

FIG. 5 is a schematic view of a main part showing a fifth embodiment of the present invention.

[Fig. 6] Oxidation, which is one of the sewage treatment methods
Schematic diagram for explaining the Ditch method.

[Explanation of symbols]

 1 ... Biological reaction tank 2 ... Raw water 3,14 ... Mechanical aeration stirrer 3a, 3b ... Drive motor 4 ... Partition wall 5 ... Final sedimentation tank 9 ... Return sludge 10 ... Respiratory speed meter 11 ... Control device 13 ... Dissolved oxygen concentration meter 21 ... Drive motor

Claims (3)

[Claims] 1. Raw water is allowed to flow into a biological reaction tank consisting of an endless water channel, and the raw water is circulated with the aeration action of a mechanical aeration stirrer installed in the water channel to perform a mixed treatment with activated sludge. In a water treatment device using the oxidation-ditch method, a respiration rate meter is installed on the downstream side of the raw water inlet, and based on the measurement value of this respiration rate meter, the controller aerates and stops aeration of the mechanical aerator. An operation control method in the oxidation-ditch method, characterized by driving and controlling a state. 2. Raw water is allowed to flow into a biological reaction tank consisting of an endless water channel, and the raw water is circulated with the aeration action of a mechanical aeration stirrer installed in the water channel to perform a mixed treatment with activated sludge. In a water treatment device using the oxidation-ditch method, a respiration rate meter is installed upstream of the mechanical aeration stirrer, and a dissolved oxygen concentration meter is installed downstream of the mechanical aeration stirrer. When the measured value of is high, the oxygen supply by the mechanical aeration stirrer is controlled to increase, while when the measured value of the respiration rate meter is low, the oxygen supply is controlled to reduce the dissolved oxygen. Oxidation ditch characterized by predicting the position where the dissolved oxygen concentration becomes zero from the measured value of the concentration and the respiration rate value and drivingly controlling the aeration and aeration stop state of the mechanical aeration mixer Operation control method in. 3. The raw water is introduced into a biological reaction tank consisting of an endless water channel, and the raw water is circulated with the aeration action of a mechanical aeration stirrer installed in the water channel to perform mixed treatment with activated sludge. In the water treatment device by the oxidation-ditch method, a plurality of mechanical aerators and respiration rate meters are installed in the biological reaction tank, and based on the measured values of this respiration rate meter,
An operation control method in an oxidation ditch method, characterized in that the control device individually drives and controls aeration and aeration stop states of a plurality of mechanical aeration mixers.