JPH0736918B2 - Supernatant discharge method in batch biological treatment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a supernatant liquid in a batch biological treatment for treating wastewater by repeating a cycle having at least an aeration step, a sludge static separation step and a supernatant liquid withdrawing step in a biological treatment tank. Regarding the discharge method.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 9, a biological wastewater treatment step of receiving wastewater such as sewage into the biological treatment tank, and supplying an oxygen-containing gas into the biological treatment tank. "Aeration process", "Sludge settling process" to settle the activated sludge in the biological treatment tank, and "Supernatant extraction process" to discharge the supernatant above the settling sludge from the biological treatment tank.
Even if the batch-type biological treatment is carried out by repeating the cycle including the treatment of wastewater, and the aeration process, sludge settling process, and supernatant removal process, wastewater is always received in the biological treatment tank. Various batch-type biological treatments such as batch-type biological treatments that do not have an "accepting step", and those that add a step of making the inside of the biological treatment tank anaerobic without aeration before and after the "aeration step" are known. Has been.

In a batch type biological treatment in which a cycle of at least an aeration step, a sludge settling step and a supernatant extraction step is repeated in the biological treatment tank to perform wastewater treatment, a float type supernatant extraction tube is used. The supernatant liquid is used for withdrawal. That is, in a batch-type biological treatment apparatus having a float type supernatant withdrawal pipe, is it conventionally necessary to start and end the withdrawal of the supernatant liquid by lowering and raising the supernatant liquid withdrawal pipe 1 as shown in FIG. Alternatively, as shown in FIG. 13, the valve 3 provided at the discharge end of the supernatant liquid withdrawing pipe 2 is opened and closed based on the detection signal from the liquid level detector 4. Then, the supernatant liquid is drawn out by the biological treatment tank 5
The liquid was left to flow naturally due to the level difference between the liquid surface inside and the discharge opening ends of the supernatant liquid withdrawing tubes 1 and 2.

Therefore, the above-mentioned level difference becomes small immediately before the completion of the supernatant liquid withdrawal step where the discharge ports 1a, 2a of the supernatant liquid withdrawing pipes 1, 2 and the sludge interface S approach, and the supernatant liquid withdrawing flow rate (flow velocity) is reduced. ) Is small, and the inclusion of sludge can be avoided. Further, by forming the floats 1b and 2b of the supernatant liquid withdrawing pipes 1 and 2 in an annular shape, the scum floating on the supernatant liquid has an outlet 1 of the supernatant liquid withdrawing pipes 1 and 2.
There was also an advantage that it could be prevented from flowing into a, 2a.

[0005]

However, in the above-mentioned conventional biological treatment method, since the supernatant liquid is withdrawn by natural flow as described above, the withdrawal flow rate is large at the initial stage of withdrawal. Therefore, the activated sludge is below a predetermined level. It is the actual situation to start the supernatant withdrawal step after the sludge is prevented from being entrained up to the level (for example, about half or less of the liquid level in the stationary separation step) and the sludge removal step is started. There is a problem that the static separation step and the supernatant liquid withdrawing step take a long time, and the withdrawal time is fixed and cannot be adjusted according to the situation such as when the sedimentation property of sludge changes.

The present invention has been made in view of the above circumstances, and can discharge the supernatant liquid from the biological treatment tank at a slow control rate to prevent sludge from being entrained. The purpose is to provide a method.

[0007]

In order to achieve the above object, the present invention performs wastewater treatment in a biological treatment tank by repeating a cycle including at least an aeration step, a sludge precipitation step and a supernatant liquid withdrawal step. In the batch type biological treatment, the organism provided in the biological treatment tank has a float and a supernatant liquid outlet at its tip portion, at least the tip portion follows the fluctuation of the water level, and the other end of the organism in the treated water tank. A supernatant discharge method in which the supernatant of the above-mentioned biological treatment tank is drawn out by a supernatant draw-out pipe that opens at a position below the lower limit level of the supernatant of the biological treatment tank. The liquid of the supernatant of the treated water tank drawn out from the biological treatment tank so that the speed becomes slower than the natural flow rate based on the difference between the liquid level of the biological treatment tank and the level of the opening end of the supernatant drawing tube. Surface is the above supernatant liquid extraction tube opening And configured to control the emissions of supernatant received in the treating tank in a state of beyond.

[0008]

[Function] When the liquid level of the supernatant of the treated water tank drawn from the biological treatment tank exceeds the opening end of the above supernatant extraction tube, the supernatant of the biological treatment tank and the treated water tank are removed. The clear fluid is in a U-shaped tubular communication state through the supernatant drawing tube. In this state, by controlling the liquid level of the treated water tank (the discharge amount of the supernatant liquid received in the treated water tank), the supernatant liquid withdrawal rate from the biological treatment tank can be adjusted to the liquid surface level of the biological treatment tank and the supernatant liquid. It is possible for the first time to make it slower than the natural flow velocity based on the difference from the level at the opening end of the liquid drawing pipe.

That is, when the supernatant liquid of the biological treatment tank and the drawn supernatant liquid of the treated water tank are brought into a U-shaped tubular communication state via the supernatant liquid drawing pipe, the supernatant liquid from the biological treatment tank is Since the drawing speed is controlled by the difference between the liquid level in the biological treatment tank and the liquid level in the treated water tank, the conventional method is based on the difference between the liquid level in the biological treatment tank and the level at the open end of the supernatant drawing tube. Inevitably slower than the natural flow rate of. In particular, if the discharge amount (discharge speed) of the supernatant liquid received in the treated water tank is made slower, for example, the liquid levels of the biological treatment tank and the treated water tank will be substantially the same (balanced), and The amount of the supernatant drawn is approximately equal to the amount discharged from the treated water tank.

Therefore, the supernatant liquid can be drawn out with a smaller drawing amount (flow velocity) than in the case of the conventional natural flow based on the difference between the liquid level of the biological treatment tank and the level of the opening end of the supernatant drawing pipe. As a result, the amount of sludge mixed in the supernatant liquid is further reduced than before. Furthermore, even if the discharge rate (flow velocity) of the supernatant liquid received in the treated water tank is made extremely high on the way due to a mistake, etc., the amount (rate) of withdrawal of the supernatant liquid from the biological treatment tank will be increased. Even if the liquid level in the treated water tank drops below the opening of the supernatant drawing tube, the conventional natural flow rate based on the difference between the level of the biological treatment tank and the level of the supernatant drawing tube opening end. The supernatant liquid can be safely withdrawn without being affected by the above-mentioned high discharge speed from the treated water tank, being restricted by (speed).

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a batch type biological treatment apparatus for carrying out the present invention will be described with reference to FIGS. In the figure, 10 is a biological treatment tank. In the biological treatment tank 10, a cycle consisting of a raw wastewater receiving process, an aeration process, a sludge static separation process and a supernatant liquid withdrawing process shown in FIG. 9 is repeated. Has become. Then, inside the biological treatment tank 10, a float 11 and a supernatant liquid outlet 12 are provided at the tip, and the base end is connected to a communication pipe 13 to communicate with the outside of the biological treatment tank 10. 14 is provided and the biological treatment tank 10
On the upper part of the tank wall 10a, a tilting device 15 for tilting the supernatant drawing pipe 14 is installed. The communication pipe 13 constitutes a part of the supernatant drawing pipe 14. Further, as is well known, the raw waste water may be received during the aeration step, the stationary separation step, and the supernatant drawing step.

The supernatant liquid withdrawing pipe 14 is provided with a straight pipe 14a having a predetermined length, and a collecting pipe 14c having the outlet 12 connected to the end of the straight pipe 14a through a bend pipe 14b of 45 degrees. A 90-degree bent pipe 14d is connected to the base end of the pipe 14a, and the bent pipe 14d at the base end is connected to the bend pipe of the communicating pipe 13 fixed to the tank wall 10a via a rotary joint 14e. It is connected to rotate up and down. A pair of left and right connecting plates 14f and 14f are fixedly attached to the liquid collecting pipe 14c, and 4 above the liquid collecting pipe 14c.
The float 11 formed by combining the book pipes 11a, ... In a rectangular ring shape is passed to the left and right pipes 11a facing each other so that the outlet 12 of the liquid collecting pipe 14c is located below the center of the float 11. The pair of left and right mounting plates 11b, 11b attached by connecting the connecting plates 14f, 14f
To the connecting plate 14f, 1
It is provided to be rotatable up and down with respect to 4f.

The raising and lowering device 15 is formed of an angle member, and is provided with a support base 16 fixedly installed on the upper part of the tank wall 10a of the biological treatment tank 10, and a rod at the center of the upper part of the support base 16. Air cylinder 17 fixedly attached with 17a facing downward, and left and right of a pair of front and rear diamond-shaped attachment plates 19, 19 fixed to the tip of rod 17a of this air cylinder 17 via a connecting member 18. A pair of left and right movable sheaves 20a, 20b which are attached to each other with their axes oriented in the front-rear direction and are rotatable in the same vertical plane, and a support base so as to be positioned slightly below the extension end of the rod 17a of the air cylinder 17. 16, a fixed pulley 21 that is attached with its axis lined up and down and is rotatable in the same vertical plane as the movable pulleys 20a and 20b, and the left movable pulley 20a. From the stationary pulley 21 to the right movable pulley 20b, one end is connected to the connecting shaft 14g of the supernatant withdrawing pipe 14 via a thimble 22a, and the other end is connected to the support frame 16 It is composed of a wire rope 22 connected to two weights 24 inserted inside a guide tube 23 provided vertically on the lower surface.

The speed controller 25a, 25b is provided on the cylinder body 17b of the air cylinder 17.
Are connected to two air pipes 26a and 26b, and the two air pipes 26a and 26b are connected to the air supply pipe 2
Solenoid switching valve 29 connected to compressed air source 28 by 7
As shown in FIG. 10, the compressed air is supplied to the cylinder body 17b through the lower air pipe 26b to contract the rod 17a, and the movable pulley 20a,
20b is lifted and separated from the fixed pulley 21,
As shown in FIG. 1, the electromagnetic switching valve 29 is switched to supply compressed air from the upper air pipe 26a to the cylinder body 17b, thereby extending the rod 17a to move the movable pulley 20a,
It is possible to lower 20b to bring it closer to the fixed pulley 21.

Further, a stopper 30 composed of a pipe having a diameter smaller than that of the weight 24 or a member having a U-shaped cross section when viewed from above is provided at the joint portion of the guide tube 23 to the support frame 16. Weight 24 is guide tube 2
It does not come out from 3 upwards.

Further, guide rails 31, 31 formed by arranging a pair of left and right angle members facing each other are additionally provided on the front side and the rear side inside the support frame 16, while
At the upper and lower parts of the mounting plates 19 and 19 and the connecting member 18, wheels 32b and wheels 32b and 32a are provided at both ends of the axles 32a and 32a, respectively.
Guide wheels 32, 32 provided with 32b are attached with their axes directed forward and backward, and the guide wheels 32, 32 move up and down along the guide rails 31, 31. Further, the biological treatment tank 10 is further provided with a first level switch 33 for detecting when the level of the supernatant liquid reaches the supernatant liquid withdrawal lower limit level LWL. The electromagnetic switching valve 29 is switched to the position shown in FIG.

On the other hand, next to the biological treatment tank 10, a treated water tank 34 in which the outer end of the communication pipe 13 is exposed.
A (supernatant tank) is installed, and a pump 36 having a discharge pipe 35 connected to the discharge side is installed at the inner bottom portion of the treated water tank 34. A flow meter 37 is attached to the discharge pipe 35.
And a flow rate adjusting valve 38 whose opening is adjusted by a signal from the flow meter 37, a circulation pipe 39 for returning the supernatant liquid to the treated water tank 34 is connected, and an orifice 39a is provided in the circulation pipe 39. Has been.

The treated water tank 34 includes the treated water tank 3
The upper level switch 40a that detects when the liquid level in 4 reaches a predetermined upper limit level H ₂ WL and activates the pump 36, and the liquid level in the treated water tank 34 is a predetermined lower limit level L ₂ WL. Lower level switch 40b that detects this when the
And the upper level switch 40a and the lower level switch 40b detect the liquid level of the treated water tank 34 and configure the liquid level detection device 40 that stops the pump 36 based on the detection signal. is doing.

Here, the communication pipe 13 provided in the treated water tank 34
The mounting height of the open end may be equal to or lower than the lower limit level LWL of the supernatant withdrawal in the biological treatment tank 10, but the settled sludge interface S at the end of the sludge static separation step and the lower limit level LWL of the supernatant withdrawal. It is preferable to provide it in the vicinity of the supernatant extraction lower limit level LWL.

The capacity of the treated water tank 34 is much smaller than the amount of water treated in one cycle of the biological treatment tank 10. Furthermore, the liquid level detection position height of the lower level switch 40b (that is, the lower limit level L ₂ W of the treated water tank 34).
L) is the lower limit level LW for extracting the supernatant of the biological treatment tank 10.
It may be equal to or lower than L, and may be equal to or lower than the level of the opening end of the communication pipe 13 depending on the capacity of the treated water tank 34 and the timing of switching from natural flow to be described later to withdrawal by the pump 36. Between the same level of LWL and the lower end of the opening of the communication tube 13, preferably the same level as the supernatant withdrawal lower limit level LWL. Further, the detection position of the upper level switch 40a (that is, the upper limit level H ₂ WL of the treated water tank 34) is naturally higher than the liquid level detection position of the lower level switch 40b, and the supernatant of the biological treatment tank 10 is Flow into the treated water tank 34 through the supernatant liquid drawing pipe 14 and enter the biological treatment tank 10 and the treated water tank 34.
The liquid level of the liquid is equal to or less than the imaginary liquid level at which the liquid levels of (1) and (2) are equal to each other.
A level close to the lower limit level of the supernatant liquid extraction above L is preferable.

In the figure, HWL is the upper limit level of the supernatant of the biological treatment tank 10 and corresponds to the water level of the biological treatment tank 10 in the sludge static separation step.

Next, the method of discharging the supernatant liquid in the batch type biological treatment of this embodiment using the biological treatment apparatus having the above-described structure will be described. Prior to this, the operation of the erection device 15 will be described first. In order to float the supernatant liquid withdrawing pipe 14 above the liquid surface by the inversion device 15, the electromagnetic switching valve 29 is moved to the position shown in FIG. 1 and compressed air is supplied from the upper air pipe 26a to the cylinder body 17b, and the rod is moved. 17a is extended. Then,
The movable pulleys 20a and 20b descend and approach the fixed pulley 21, but at the extension end of the rod 17a, the supernatant drawing pipe 14
The wire rope 22 that has been erected upward has a margin in length, which causes the supernatant liquid drawing tube 14
Is rotated downward at the rotary joint 14e and floated above the supernatant liquid surface.

At this time, the wire rope 22 is not loosened because the weight 24 is provided at the end thereof, but when the liquid level of the supernatant liquid is at the supernatant liquid extraction upper limit level HWL, FIG. As described above, the weight 24 descends to the lower end of the guide tube 23.

In order to raise the supernatant drawing pipe 14 upward by the raising / lowering device 15, the electromagnetic switching valve 29 is used as shown in FIG.
Switch to the 0 position. Then, the compressed air enters the cylinder body 17b from the lower air pipe 26b, and then the rod 1
7a contracts, whereby the movable pulleys 20a, 20b rise and move away from the fixed pulley 21. Since the wire rope 22 is wound around the movable sheaves 20a and 20b and the fixed sheave 21 alternately, the wire rope 22 is pulled up as the movable sheaves 20a and 20b rise, and the weight 24 is first pulled.
When the weight hits the stopper 30 and the weight 24 is locked by the stopper 30 and cannot rise further, this time, the supernatant liquid withdrawing pipe 14 is pulled up via the wire rope 22 and the standing state as shown in FIG. Become.

Next, in the biological treatment apparatus having the above structure,
A case will be described in which the supernatant of the biological treatment tank 10 whose liquid level is at the upper limit level HWL for extracting the supernatant is discharged. In this case, the reversing device 15 is operated as described above to float the supernatant liquid drawing tube 14 above the liquid surface. Then, when the lower limit level L ₂ WL of the treated water tank 34 is equal to or lower than the level of the open end of the communication pipe 13, the supernatant liquid in the biological treatment tank 10 is
Due to the level difference between the liquid level of the biological treatment tank 10 and the opening end of the communication pipe 13, the liquid enters the supernatant liquid drawing pipe 14 from the outlet 12 and flows down naturally, and then flows into the treated water tank 34 via the communication pipe 13. . Further, when the liquid level of the treated water tank 34 exceeds the opening end of the communication pipe 13, or the lower limit level L ₂ WL of the treated water tank 34 is set to the state of exceeding the level of the opening end of the communication pipe 13 from the beginning. Then, the supernatant liquid of the biological treatment tank and the drawn supernatant liquid of the treated water tank become in a U-shaped tubular communication state through the above-mentioned supernatant liquid extraction pipe, and the supernatant liquid is withdrawn from the biological treatment tank. The speed is regulated by the difference between the liquid level of the biological treatment tank and the liquid level of the treated water tank, and the above natural flow rate is based on the difference between the liquid level of the biological treatment tank and the level of the supernatant drawing pipe opening end. Inevitably slower. Since the capacity of the treated water tank 34 is extremely small, the liquid level of the treated water tank 34 immediately rises, the upper level switch 40a is turned on, and the pump 36 is activated, whereby the supernatant liquid in the treated water tank 34 is discharged through the discharge pipe 35. To be done.

In this case, normally, the liquid surface levels of the biological treatment tank 10 and the treated water tank 34 substantially match (balance) with the discharge.
The discharge of the supernatant liquid by the pump 36 is adjusted so as to descend. That is, the discharge amount (drainage rate) of the supernatant liquid received in the treated water tank is determined based on, for example, the difference between the liquid surface level of the biological treatment tank and the liquid surface level of the treated water tank. If the speed is slower than the speed, the liquid levels of the biological treatment tank and the treated water tank will be substantially the same (balanced), and the amount of supernatant liquid withdrawn thereafter will be substantially equal to the amount discharged from the treated water tank. Therefore, the supernatant can be withdrawn with a significantly smaller withdrawal amount (flow velocity) than in the case of conventional natural flow based on the difference between the liquid level of the biological treatment tank and the level of the supernatant of the supernatant withdrawal pipe, The amount of sludge mixed in the supernatant liquid is further reduced than before. When the sedimentation property of the sludge changes, the discharge rate from the treated water tank is adjusted according to the situation to adjust the withdrawal rate of the supernatant of the biological treatment tank 10. That is, the withdrawal flow rate of the supernatant of the biological treatment tank 10 can be adjusted by adjusting the discharge flow rate of the supernatant liquid by the pump 36, and the discharge flow rate of the supernatant liquid with the pump 36 is adjusted by releasing the discharge. It can be performed by a known means such as rotation control of the flow rate adjusting valve 38 provided in the pipe 35 or the pump 36.

On the other hand, when the supernatant liquid withdrawal progresses and the liquid level of the biological treatment tank 10 reaches the supernatant liquid extraction lower limit level LWL, the first level switch 33 of the biological treatment tank 10 detects this and the detection signal thereof. Thus, the inversion device 15 is activated to raise the supernatant withdrawing tube 14 and stop the withdrawal of the supernatant. Further, the pump 36 is operated until the liquid level of the treated water tank 34 reaches the lower limit level L ₂ WL and the lower level switch 40b detects this.

As described above, in the supernatant discharging method in the batch type biological treatment of this embodiment, the supernatant liquid is extracted from the biological treatment tank 10 and the communicating pipe 1
3 From the natural flow-down based on the level difference from the opening end and the drawing of the supernatant liquid based on the difference between the liquid level of the biological treatment tank and the liquid level of the treated water tank, the liquid level of treated water tank 10 immediately rises to the above level. Since the withdrawal control by the pump 36 in a state of exceeding the opening end of the clear liquid withdrawal tube can be changed, by adjusting the discharge flow rate of the supernatant liquid from the treated water tank 34 by the pump 36,
The withdrawal flow rate of the supernatant liquid from the biological treatment tank 10 can be adjusted in advance.

As described above, since the supernatant liquid is drawn out at a drawing flow rate (flow velocity) smaller than the natural flow due to the level difference between the liquid level in the biological treatment tank 10 and the opening end of the communication pipe 13, Contamination of sludge is further reduced than before, and even if sludge is not completely settled to a predetermined level below the lower limit level LWL of supernatant extraction in the stationary separation step, this still separation step ( For example, when the sludge settles only 40% to 70% of the predetermined level)
However, the supernatant drawing process can be started in parallel with the stationary separation process, and as a result, the total time of the stationary separation process and the supernatant drawing process can be shortened. Further, the timing of switching from the natural flow down to the extraction by the pump 36 can be optimally set by adjusting the mounting positions of the upper level switch 40a and the lower level switch 40b.

Further, the supernatant liquid of the biological treatment tank 10 flows into the treated water tank 34 through the supernatant liquid withdrawal pipe 14 because the liquid surface of the biological treatment tank 10 and the liquid surface of the treated water tank 34 or the communicating pipe 13 are provided. Since the liquid level in the biological treatment tank 10 becomes close to the supernatant liquid extraction lower limit level LWL, even if the pump 36 is operated at a large discharge flow rate for some reason, The liquid withdrawal amount is restricted by the flow due to the level difference between the liquid surface of the biological treatment tank 10 and the liquid surface of the treated water tank 34, and even if the liquid surface in the treated water tank 34 drops below the opening end of the communication pipe 13. Is restricted by the conventional natural flow rate (velocity) based on the difference between the liquid level of the biological treatment tank 10 and the level of the communication pipe 13 at the open end, and is not affected by the above-mentioned fast discharge rate from the treated water tank, Safe withdrawal of supernatant It takes place.

By the way, in the above embodiment, when the lower level switch 40b is provided at the same level as the first level switch 33 of the biological treatment tank 10 or in the vicinity of the level, the first level switch 33 of the biological treatment tank 10 and the above The lower level switch 40b can be processed by one level switch, and either one can be omitted.
Further, instead of the first level switch 33 or the lower level switch 40b, an integrated flow meter is attached to the discharge side pipe of the low flow rate pump 36, whereby the amount of the supernatant liquid discharged in one cycle of the biological treatment tank 10 is equal. Liquid volume is treated water tank 3
The pump 36 may be stopped upon detection of discharge from the pump 4.

Further, in the above-mentioned embodiment, the upper level switch 40a is used as means for starting the pump 36. However, the liquid levels of the biological treatment tank 10 and the treated water tank 34 are made to coincide with each other at the initial stage of withdrawing the supernatant liquid, and the communicating pipe is no longer used. Since it is possible to prevent the supernatant liquid from flowing inside 13, a timer is used instead of the above-mentioned upper level switch 40a, and this timer gives a signal indicating that the supernatant liquid extraction has started, for example, an electromagnetic switching valve of the inversion device 15. Alternatively, the pump 36 may be started at a predetermined time from the time when the operation signal of 29 is received. Therefore, the control means for starting and stopping the pump may be one that can directly or indirectly detect the liquid surface of the treated water tank 34. Further, of course, the start and end of the supernatant liquid withdrawal may be performed by opening and closing the valve 3 as shown in FIG.

Furthermore, the biological treatment tank 10 is provided with a liquid level meter and a sludge interface meter capable of continuously or intermittently measuring the liquid level and the sludge interface, and based on the level difference between the liquid surface and the sludge interface. The controller may control the rotation speed of the flow rate adjusting valve 38 or the pump 36 to continuously control the discharge amount of the supernatant liquid by the pump 36.

Further, another bent pipe or the like is connected to the open end of the communicating pipe 13 through a rotary joint, and the rotational position of the bent pipe or the like is changed to thereby increase the height of the open end of the communicating pipe. It can also be adjustable. In the present invention, the structure of the supernatant liquid withdrawal pipe may be integrated with the communication pipe as shown in FIG. 13, for example.

[0035]

Industrial Applicability As described above, the method of discharging a supernatant liquid in the batch type biological treatment of the present invention repeats a cycle having at least an aeration step, a sludge precipitation step and a supernatant liquid withdrawal step in the biological treatment tank. In a batch type biological treatment in which sewage treatment is performed by using a biological treatment tank, the tip portion has a float and a supernatant liquid outlet, and at least the tip portion follows fluctuations in water level, and the other end is A method of discharging a supernatant liquid of the biological treatment tank by a supernatant liquid extraction pipe that opens at a position below the lower limit level of the supernatant liquid extraction in the biological treatment tank of the treated water tank. Of the treated water tank drawn out from the biological treatment tank so that the supernatant discharge speed of the biological treatment tank becomes slower than the natural flow rate based on the difference between the liquid level of the biological treatment tank and the level of the opening of the supernatant drawing tube. The liquid level of the supernatant is above Since it is configured to control the discharge amount of the supernatant liquid received in the treated water tank above the opening of the clear liquid drawing tube, it is possible to reliably prevent the mixing of sludge into the supernatant liquid, The withdrawal of the supernatant can be started even during the stationary separation step, and as a result, the total time of the stationary separation step and the supernatant withdrawal step can be shortened. In addition, the supernatant liquid withdrawing time can be adjusted according to the condition of sludge properties.

[Brief description of drawings]

FIG. 1 is a sectional view of a batch type biological treatment apparatus for carrying out the present invention.

FIG. 2 is a plan view of a supernatant drawing tube.

FIG. 3 is likewise a side view of the cross section of the main part.

FIG. 4 is a sectional view taken along the line IV-IV in FIG.

FIG. 5 is an enlarged view of the tilting device.

6 is a sectional view taken along the line VI-VI of FIG.

7 is a sectional view taken along the line VII-VII of FIG.

FIG. 8 is a view on arrow VIII-VIII in FIG.

FIG. 9 is an explanatory diagram of a wastewater treatment process.

FIG. 10 is an overall cross-sectional view for explaining the operation.

FIG. 11 is also an overall cross-sectional view for explaining the operation.

FIG. 12 is a schematic sectional view showing a conventional example.

FIG. 13 is a schematic sectional view showing another conventional example.

[Explanation of symbols]

 10 Biological Treatment Tank 11 Float 12 Extraction Port 14 Supernatant Extraction Pipe 34 Treated Water Tank

Claims (1)

[Claims] 1. A batch type biological treatment in which a cycle of at least an aeration step, a sludge precipitation step, and a supernatant liquid withdrawing step is repeated in the biological treatment tank to perform wastewater treatment, and the tip is provided in the biological treatment tank. At least the tip part follows the fluctuation of the water level with a float and a supernatant liquid outlet in the part, and the other end opens at a position below the lower limit level of the supernatant liquid withdrawal in the biological treatment tank of the treated water tank. A method of discharging a supernatant liquid by extracting a supernatant liquid of the biological treatment tank by a supernatant liquid extraction pipe, wherein a supernatant discharge speed from the biological treatment tank is a liquid level of the biological treatment tank and a supernatant liquid extraction. The liquid level of the supernatant of the treated water tank drawn out from the biological treatment tank exceeds the above-mentioned supernatant drawing tube opening end so as to be slower than the natural flow rate based on the difference from the level at the tube opening end. Discharge of the supernatant received in the treated water tank A method for discharging a supernatant liquid in a batch-type biological treatment, which comprises controlling an output amount.