JPH03137993A - Air flow rate controlling method for super deep aeration tank - Google Patents

Abstract

PURPOSE:To stably keep constant air circulating rate by installing a Doppler-type flow rate measure in a side wall of a head tank which forms a part of a circular flowing route and controlling the air introduction rate for circulation using the determined value as an index. CONSTITUTION:When air for circulation is introduced into an ascendent flow route 6 of a super deep aeration tank 1 filled with a raw liquid through a supplying tube 10, the liquid circulates in a head tank 4 owing to air lift effect, flows to a descendent flow route 5 through a connecting hole 7 to become a descending flow, circulates while mixed with a raw liquid and a returned sludge supplied from a flowing route 16 and 17, respectively, and air supplying is gradually switched from a supplying tube 10 to a supplying tube 9 to keep a circulating rate to carry out biological oxidation treatment. In this case, a controlling apparatus 15 controls the circulating rate from the supplying tube 10 depending on a value measured by a Doppler-type flow rate measure installed in a side wall of the head tank 4 as an index and controls treatment air flow rate from the supplying tube 9 by measured value of a dissolved oxygen concentration measure 13 as an index. In this way, circulating rate is stably retained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the amount of circulating air in an ultra-deep aeration tank for biologically treating organic wastewater.

[Conventional technology]

Conventionally, an ultra-deep aeration tank with an extremely deep liquid depth has been used as a device for biologically treating sewage and various industrial wastewater using the activated sludge method. The ultra-deep aeration tank has a descending channel into which the stock solution is introduced, an ascending channel communicating with the descending channel at its lower end, and a communicating hole connected to the descending channel at the upper end of the ascending channel. A circulation flow path is formed by a head tank, and a processing air supply pipe introduces air for biological oxidation into a relatively deep portion of the descending flow path, and a liquid circulation is controlled to a relatively shallow portion of the upward flow path. It is a vertical aeration tank with a liquid depth of 40 to 250 nm, and is equipped with a circulating air supply pipe that introduces air for liquid circulation.The aeration section is mainly buried underground. The circulating flow of the liquid in the aeration tank is achieved by introducing circulating air from the circulating air supply pipe provided in the ascending flow path at the time of startup to induce an upward flow due to the air lift effect. During operation, the amount of circulating air is usually gradually reduced, and at the same time, the amount of processing air is gradually increased by introducing processing air from the processing air supply pipe provided in the descending flow path. As it descends through the channel, it becomes fine bubbles due to an increase in the water pressure in the channel and dissolves in the liquid, and when it circulates in the ascending channel and rises, the water pressure decreases, contrary to the above, generating lick bubbles. The liquid aggregates and becomes coarse, creating a difference in the apparent specific gravity of the liquid between the descending flow path and the ascending flow path, thereby maintaining a circulating flow. However, if the flow rate or organic matter content of the stock solution is high, it is necessary to increase the amount of air to be processed, but if only the amount of air to be processed is increased, the apparent specific gravity of the liquid in the descending flow path and the ascending flow path will be reversed. There is a risk that the liquid will rise up the downward flow path and cause backflow. Therefore, it is necessary to prevent backflow by increasing the amount of circulating air in accordance with the amount of air being processed. Conventionally, the above-mentioned switching and control of the amount of introduced air has been carried out by manual operation based on experience, such as by visual measurement, since there is no instrument that can accurately measure the state of liquid circulation.

[Problem to be solved by the invention]

With conventional manual control of the amount of air introduced into the descending flow path and the ascending flow path, it is difficult to maintain an optimal circulation flow rate. In addition, it is possible to sufficiently follow changes in the liquid volume or organic matter content of the stock solution for some reason; - In boat fishing, there is a loss in power costs due to excessive introduction of circulating air into the ascending channel.

In order to always introduce an appropriate amount of circulating air, it is preferable to measure the circulating flow velocity using a current meter and use the measured value as an indicator for control. In addition, due to the turbulence in the flow path, a large amount of scattered air bubbles were present, and an appropriate current meter could not be selected.

In view of the above-mentioned circumstances, the present invention was made as a result of careful consideration of an appropriate current meter and an optimal installation position in order to accurately grasp the circulating flow velocity and ensure that the optimum amount of circulating air is introduced at all times. be.

[Means to solve the problem]

The gist of the present invention is a head having a descending channel into which a stock solution is introduced, an ascending channel communicating with the descending channel at its lower end, and a communicating hole connected to the descending channel at the upper end of the ascending channel. Ultra-deep aeration comprising a processing air supply pipe that forms a circulation flow path with a tank and introduces processing air into the downward flow path, and a circulating air supply pipe that introduces liquid circulation air into the upward flow path. Air amount control for an ultra-deep aeration tank, characterized in that a Doppler flow meter is installed on the side wall of the head tank in the tank, and the amount of circulating air introduced is controlled using the measured value of the Doppler flow meter as an index. It's a method.

[For production]

When circulating air is introduced from the circulating air supply pipe into the ascending flow path of the ultra-deep aeration tank filled with stock solution, an upward flow is generated due to the air lift effect, and the solution is circulated. Biological oxidation treatment is performed by gradually switching the air supply from the circulating air supply pipe to the processing air supply pipe side and introducing the processing air into the downward flow path. In controlling each of the above air amounts and timely air amounts, the amount of processed air is mainly determined by measuring the amount of dissolved oxygen using a dissolved oxygen concentration meter, and the amount of circulating air is determined by measuring the circulating fluid flow rate using a Doppler flow meter. It is determined using the value as an index, and is performed by operating the air amount control valve provided in each supply pipe via a control device. In the measurement of circulating flow velocity using the Doppler current meter, an ultrasonic wave emitted from a transmitting transducer into a circulating flow encounters and is reflected by mixed solid particles while propagating in the circulating flow. The reflected waves produced by the reflection generate a phase difference based on the Doppler effect due to the flow velocity, and the circulating flow velocity is measured from the phase difference value.

〔Example〕

The details will be explained below based on the drawings. FIG. 1 is a system diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing the AA homeland of FIG. 1.

1 is an inner cylinder 2 which is open at the upper and lower ends and has a communication hole 7 with the head tank 4 on the side; an outer cylinder 3 with a bottom surrounding the inner cylinder; and an outer cylinder 3 connected to the upper end of the outer cylinder 3. It is an ultra-deep aeration tank with a liquid depth of 40 to 250 m, consisting of a head tank 4 and a head tank 4. A descending flow path 5 runs inside the inner cylinder 2, and an upward flow path runs between the inner cylinder 2 and the outer cylinder 3. 6, and a circulation flow path is formed via the head tank 4.

The head tank 4 also has a partition wall 8a so that the circulating fluid from the ascending channel 6 swirls within the head tank 4 and flows into the descending channel 5.
, 8b is provided. Reference numeral 9 denotes a processing air supply pipe that introduces processing air into a relatively deep part of the descending passage 5, and lO indicates a circulating air supply pipe that introduces circulating air into a relatively shallow part of the ascending passage 6. It is equipped with quantity control valves 11a and llb, and is connected to a compressor 12 for supplying air. A dissolved oxygen concentration meter 13 for measuring dissolved oxygen in the circulating fluid is installed in the head tank 4, and a Doppler flow meter 14 for measuring the flow rate of the circulating fluid is installed on the side wall of the head tank 4. Ru. If the side wall of the head tank 4 is made of a material such as concrete that is difficult for ultrasonic vibrations to propagate, it is preferable to replace a portion of the side wall with a metal plate and mount the Doppler flowmeter 14 thereon. A control device 15 controls the amount of air to be processed and the amount of circulating air based on the amount of dissolved oxygen measured by the dissolved oxygen concentration meter 13 and the amount of liquid flow rate measured by the Doppler flow meter 14. The above-mentioned Doppler current meter transmits ultrasonic waves into the circulating flow from the transmitting transducer,
A device that receives reflected waves reflected by solid particles mixed in the circulating flow using a receiving transducer, and measures the flow velocity of the circulating flow from the phase difference between the emitted wave and the received wave whose phase is shifted due to the Doppler effect. While the ultrasonic waves emitted from the transmitting transducer propagate in the circulating flow, the phase shifts due to the Doppler effect, and a known device is used to receive and measure the ultrasonic waves by a receiving transducer disposed opposite to each other.

The operation of biologically treating the stock solution using the ultra-deep aeration tank configured as described above will be described in detail below.

When circulating air is introduced from the circulating air supply pipe IO into the ascending channel 6 of the ultra-deep aeration tank 1 filled with the stock solution, an upward flow is generated due to the air lift effect. The liquid flow swirls inside the head tank 4, flows into the downward flow path 5 through the communication hole 7, becomes a downward flow, makes a U-turn at the lower end of the downward flow path 5, enters the upward flow path 6, becomes an upward flow, and circulates. will be carried out. To process the raw solution, the raw solution is supplied from the raw solution flow path 16, the sludge from the return sludge flow path 17 is supplied into the descending flow path 5, and the treated liquid is supplied to the solid liquid (not shown) in the subsequent stage from the treatment liquid flow path 18 provided in the head tank 4. This is carried out continuously by the operation of sending the air to a post-processing device such as a separation device, but the air supply is gradually switched from the circulating air supply pipe 1o to the treated air supply pipe 9 side, and the treated air is gradually introduced into the descending flow path 5. By increasing the amount, it is possible to maintain the circulating amount and perform biological oxidation treatment. That is, the introduced processing air descends through the downward flow path 5 along with the circulating flow, becomes fine bubbles due to the increase in water pressure, and dissolves in the liquid, and when it circulates back to the upward flow path 6 and rises, it reverses the above process. The water pressure decreases, bubbles are generated, and the liquid aggregates and coarsens, creating a difference in the apparent specific gravity of the liquid between the descending channel 5 and the ascending channel 6, thereby maintaining the circulating flow. Also, since the liquid depth is extremely deep, compared to a normal aeration tank,
The concentration of liquid oxygen in the liquid is high, the activity of aerobic microorganisms becomes active, and biological oxidation treatment is carried out effectively. The amount of circulating air from the circulating air supply pipe IO is determined by the measured value of the circulating fluid flow rate by the Doppler flow meter 14 installed on the side wall of the head tank 4, and the amount of air being processed from the processing air supply pipe 9 is determined by , the respective air amount control valves 11a, Ilb are controlled via the control device 15 using the measured value of the amount of dissolved oxygen in the circulating fluid by the dissolved oxygen concentration meter 13 disposed mainly in the head tank 4 as an index.
is automatically controlled by the operation.

〔Effect of the invention〕

The present invention has the following effects.

b) By installing a Doppler type current meter on the side wall of the head tank, its installation work and maintenance are facilitated, and a large amount of air bubbles mixed in the ascending flow that impede flow rate measurement are separated and broken in the head tank. Since the circulating flow is rectified within the head tank, the flow velocity can be measured accurately.

(Note) The amount of circulating air is automatically controlled using the measured value of the Doppler flowmeter as an indicator, and the amount of processed air is automatically controlled using the measured value of the dissolved oxygen concentration meter as an indicator. It is possible to always control the amount of circulating air and the amount of processed air to be optimal in response to fluctuations, thereby reducing power costs and maintaining a stable circulating flow rate.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an embodiment of the present invention, and FIG. 2 is a tax line diagram taken along line A-A in FIG. 1; Ultra-deep aeration tank, 2: Inner cylinder, 3; Outer cylinder, 4; Head tank, 5; Downflow passage, 6: Upflow passage, 7: Communication hole, 8a
, 8b; Partition wall, 9; Processing air supply pipe, 10; Circulating air supply pipe, lla, llb, air volume control valve, 12; Compressor, 13; Dissolved oxygen concentration meter, 14; Doppler flow meter, 15; Control Apparatus, 16. Raw solution flow path, 17, return sludge flow path, 18; treated liquid flow path.

Claims (1)

[Claims] A circulating flow is created by a descending channel into which the stock solution is introduced, an ascending channel communicating with the descending channel at its lower end, and a head tank that is connected to the upper end of the ascending channel and has a communication hole with the descending channel. In the ultra-deep aeration tank, the head A method for controlling the amount of air in an ultra-deep aeration tank, comprising: installing a Doppler current meter on the side wall of the tank; and controlling the amount of circulating air introduced using the measured value of the Doppler current meter as an index.