JPH05138187A - Device for controlling flow rate of returned sludge - Google Patents

Abstract

PURPOSE:To homogenize the conditions relating to the amount of activated sludge of the respective aertors in a plurality of sewage disposal systems. CONSTITUTION:In a sewage disposal controlling device equipped with a plurality of sewage disposal systems wherein sewage is introduced into aerators and mixed with returned sludge and air is supplied into the aerators to perform purification of sewage, the necessary flow rate of returned sludge is calculated by algorithm for maintaining the ratio of the flow rate of returned sludge constant for the flow rate of sewage introduced into the aerators in the arithmetic devices 10A, 10B of requested returned sludge. The measured flow rate arithmetic devices 11A, 11B calculate the ratio of the measured value for the request amount of returned sludge from both the output of these arithmetic devices and the output signals of the flow meters 6A, 6B of returned sludge. The ratio of both the necessary flow rate of returned sludge and the measured value in a plurality of sewage disposal systems is calculated by an arithmetic device 12 for regulating the rate of flow rate so that the ratio is made constant. The operation state of the sewage disposal systems is homogenized by opening and closing the control valves 7A, 7B of returned sludge in the sewage disposal systems wherein the ratio of the measured flow rate is early made large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a returning sludge flow rate control device in sewage treatment by the activated sludge method.

[0002]

2. Description of the Related Art In a conventional sewage treatment apparatus, as shown in FIG. 2, the inflowing sewage that first flows from the settling basins 1A and 1B flows into the aeration tanks 3A and 3B. On the other hand, the activated sludge drawn from the final settling tank 4 by the returning sludge pump 5 has a flowmeter 6A,
After 6B, it is returned to the aeration tank as return sludge. The influent sewage that has flowed into the aeration tank is mixed with the activated sludge to adsorb the solid matter and soluble organic matter contained in the influent sewage to the activated sludge, and at the same time, it is decomposed by biological oxidation to purify the sewage. Such a purifying action has a plurality of aeration tanks A and B.
The mixed liquid of sewage and activated sludge flows into the final settling tank 4, and the activated sludge in the mixed solution is settled in the final settling tank.
It was scraped by a scraping machine, collected in a hopper, returned by the returning sludge pump 5, and partly discharged as excess sludge. 2A and 2B are inflow sewage flow meters, 7
A and 7B are return sludge amount control valves, and 8 is a surplus sludge drawing pump.

[0003]

In such a sewage treatment apparatus having a plurality of aeration tanks, there are a plurality of piping systems that circulate the piping from the final settling tank and return the returned sludge to the respective aeration tanks. , The pipeline resistance varies due to the difference in pipeline length of the pipeline. Therefore, when a large amount of returned sludge that exceeds the capacity of the returned sludge pump 5 is required, the amount of sludge returned to the aeration tanks 3A and 3B does not reach the required amount in both aeration tanks, but about the insufficient amount. There is a big difference. As a result, there was a large difference in the amount of activated sludge in the aeration tank, and there was a drawback that individual management of the air flow to the aeration tank and eventually a difference in the purification action occurred, making it difficult to operate the sewage treatment device. .. Therefore, an object of the present invention is to make the amount of activated sludge in each aeration tank in a plurality of sewage treatment systems uniform.

[0004]

[Means for solving the problem] First, sewage treatment control with multiple sewage treatment systems that guide the supernatant water of the sedimentation tank into the aeration tank, mix it with the returned sludge, and supply air into the aeration tank to purify the sewage. In the equipment, the return sludge ratio constant algorithm that makes the ratio of the return sludge flow rate to the aeration tank inflow sewage flow rate constant, or the MLSS concentration constant algorithm that tries to keep the MLSS concentration in the aeration tank constant by adjusting the return sludge flow rate, etc. The required return sludge calculator that calculates the required amount of returned sludge by the device, and the measured flow rate ratio calculator that calculates the ratio of the actual measured value to the required amount of returned sludge from the output of the requested return sludge calculator and the output signal of the returned sludge flow meter And the output of the measured flow rate ratio calculator of one sewage treatment system and the output of the measured flow rate ratio calculator of another sewage treatment system from the request return pollution of multiple sewage treatment systems. Has a flow rate ratio adjustment calculator for the ratio of the flow rate and the measured value constant, it is obtained as a homogeneous operating conditions of the sewage treatment system by opening and closing the respective sewage treatment system return sludge control valve.

[0005]

Therefore, the ratio of the amount of returned sludge returned to a plurality of aeration tanks to the required amount can be made the same, so that the activated sludge amount state of a plurality of aeration tanks can be made uniform and the operation of the sewage treatment device can be simplified. be able to.

[0006]

FIG. 1 shows an embodiment of the present invention. The same parts as those in FIG. 2 are designated by the same reference numerals and detailed description thereof will be omitted. In the figure, 9A and 9B are return ratio setters for setting the return ratio, 10A and 10B are required return sludge calculators for calculating the required return sludge amount from the signals from the return ratio setter and the signals of the inflow sewer meters 2A and 2B. 11A and 11B are flowmeters 6A for measuring the signal of the requested sludge calculator and the actual amount of sludge to be returned.
Measured flow rate ratio calculator that calculates the ratio of the required amount of returned sludge to the actual amount of returned sludge from the signal of 6B, and 12 is the measured flow rate of both systems from the output signals of the measured flow rate ratio calculators 11A and 11B of each aeration tank series. The flow rate adjusting calculators 13A and 13B for adjusting the ratio to be constant are control devices for opening and closing the return sludge amount adjusting valves 7A and 7B according to the output signals of the flow rate adjusting calculator. In such a returning sludge flow control device, the inflowing sewage amount of Q _A and Q _B into the aeration tanks A and B first flows into the settling tanks 1A and 1B or the aeration tanks 3A and 3B,
The inflowing sewage in the aeration tank is purified while being supplied with air from a diffusion plate (not shown), the mixed solution flows down to the final settling tank 4, the activated sludge settles in the final settling tank, and the supernatant water is out of the tank. The activated sludge that has been discharged to and settled in the above is returned to the aeration tanks 3A and 3B as return sludge. Now, if the inflow water amounts flowing into the aeration tanks A and B are Q _A and Q _B, and the return ratios α _A and α _B are set in the return ratio setters 9A and 9B,
The measured flow rate ratio calculators 10A and 10B calculate the measured flow rate ratios β _A and β _B, and output them to the flow rate ratio calculator 12, respectively. When the measured flow rate ratios of both aeration tank series are approximately equal, the sludge control valves 7A and 7B are output to the control devices 13A and 13B so as to operate at the current opening degree. Now, when the amount of sewage that flows into the settling basin first increases, the amount of sewage that flows into each aeration tank Q _A , Q _B also increases, and the requested return sludge calculators 10A, 10
The requested sludge amounts RSQ _A and RSQ _B output from _B also increase. RSQ _A = Q _A · α _A ─── (1) RSQ _B = Q _B · α _B ─── (2) RSQ = RSQ _A + RSQ _B (3) Total Return Sludge Volume RSQ is the discharge capacity of the return sludge pump 5. In case of exceeding, the return sludge amount RS _A , RS _B actually measured by the flowmeters 6A, 6B is the required return sludge amount RSQ _A , R
It becomes smaller than SQ _B , and the measured flow rate calculator 11A,
11B or the outputted β _A, β _B is smaller than 1. β _A = RS _A / RSQ _A (4) β _B = RS _B / RSQ _B (5) At this time, due to differences in the pipe length of the returned sludge pipe, it was measured that the pipe resistance of each aeration tank series was different. Flow rate β _A , β _B
Will be different. The flow rate ratio adjustment calculator 12 compares the measured flow rate ratios β _A and β _B , and outputs the target flow rate to the control device 13 having a large value so that the measured flow rate ratio becomes a small value. Upon receiving this output, the sludge control valve 7 is operated in the closing direction. For example, when β _A is larger than β _B , RS _A ^' = β _B · RSQ _A (13) is used as the target flow rate and the corrected RS _A ^' is set to 13
Output to A. At this time, the controller 13B is instructed not to open / close the sludge control valve. Therefore, the amount of returned sludge in the series with a large flow rate decreases, and the amount of returned sludge in the series with a small flow rate increases. As a result, new actually measured flow rate ratios β _A and β _B are calculated and input to the flow rate ratio adjustment calculator 12. In the flow rate adjustment calculator 12, when β _A and β _B become substantially equal to each other, the return sludge control valve 7 is output to the control device 13 so as to operate at the current opening. If β _A and β _B cannot be regarded as equal, the returned sludge control valve 7 should be set so that the measured flow rate ratio is initially large, while the other measured flow rate ratio is the same.
Is output to the control device 13 so as to operate. In this way, in a situation where the total amount of sludge to be returned is insufficient, the measured flow rate ratio can be made equal and the maximum possible value can be obtained. In the embodiment, the adjustment operation is started immediately when a difference is detected in the actually measured flow rate, but the adjustment operation may be started after the difference continues for a certain period of time. As a calculation method of the above, the method of multiplying the inflow sewage amount by the set ratio was shown, but the MLS in the aeration tank was shown.
The calculation method may be another method such as a method of calculating the amount of returned sludge so as to keep the S concentration constant.

[0007]

According to the present invention, even when the required amount of sludge to be returned exceeds the discharge capacity of the returning sludge pump,
Since the measured flow rate ratios of multiple aeration tank series can be made equal and maximized as much as possible, the conditions related to the amount of activated sludge in multiple aeration tank series will be uniform and the operation of sewage treatment equipment will be simple. Can be converted.

[Brief description of drawings]

FIG. 1 is a block diagram of a returning sludge flow rate control device showing an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional returning sludge flow rate control device.

[Explanation of symbols]

 1A, 1B, 4 Final sedimentation tank 2A, 2B Inflow sewage meter 3A, 3B Aeration tank 4 Final sedimentation tank 6A, 6B Flow meter 7A, 7B Return sludge amount control valve 8 Excess sludge extraction pump 10A, 10B Request return sludge calculator 11A, 11B Measured flow rate ratio calculator 12 Flow rate adjustment calculator 13A, 13B Control device

Claims (1)

[Claims] 1. A sewage treatment control apparatus having a plurality of sewage treatment systems for purifying sewage by first introducing the supernatant water of a sedimentation basin into an aeration tank and mixing it with return sludge to supply air to the aeration tank. Return sludge ratio constant algorithm that keeps the ratio of the returned sludge flow rate to the tank inflow sewage flow rate constant, or the MLSS concentration constant algorithm that keeps the MLSS concentration in the aeration tank constant by adjusting the returned sludge flow rate. A requested return sludge calculator that calculates the sludge flow rate, an actual flow rate ratio calculator that calculates the ratio of the actual value to the required amount of returned sludge from the output of the requested return sludge calculator and the output signal of the returned sludge flow meter, From the output of the measured flow rate ratio calculator for the sewage treatment system and the output of the measured flow rate ratio calculator for other sewage treatment systems, the required return sludge flow rate and measured values for multiple sewage treatment systems can be calculated. A return sludge flow control device comprising a flow rate adjusting calculator for keeping the ratio constant, and opening and closing the return sludge control valve of each sewage treatment system to make the operation state of the sewage treatment system uniform.