JPS6343122B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sedimentation separation method and apparatus for separating a mixed liquid after aeration into sludge and supernatant water in activated sludge treatment of wastewater.

As is well known, organic wastewater such as domestic wastewater is usually treated by an activated sludge treatment method using microorganisms. The outline of a conventional activated sludge treatment device will be explained with reference to FIG.
is a settling tank. In this device, wastewater introduced into an aeration tank 1 is first treated with microorganisms (activated sludge) while being supplied with oxygen (air), and then the treated mixture is led to a settling tank 2 where it is The sludge is allowed to settle, and the supernatant water is discharged as treated water, and the settled sludge is pulled out and returned to the aeration tank 1 for aeration treatment.

By the way, in the above activated sludge treatment, at the same time as the BOD component is removed in the aeration tank 1,
Ammonia nitrogen and organic nitrogen contained in raw water are oxidized by the action of nitrifying bacteria, and part or most of them are converted to nitrate nitrogen. In the sedimentation tank 2, almost no oxygen is supplied to the settled sludge layer 3, resulting in an anaerobic state, and a portion of the denitrification reaction occurs within this sludge layer 3 due to the action of denitrifying bacteria. There is. For this reason, in the conventional sedimentation tank 2, bubbles of nitrogen gas generated are trapped in a part of the sludge, and the apparent specific gravity of that part decreases.
There were cases where they surfaced as scum. As a result, even if the treatment in aeration tank 1 is progressing sufficiently, activated sludge gets mixed into the supernatant water (treated water) in the settling tank, causing the quality of the treated water to deteriorate in terms of BOD, COD, and SS values. There was a problem.

In addition, among general hopper-type settling tanks that are equipped with a center well, the sludge is kept so that the upper part of the settled sludge layer 3 is always kept below the lower end opening of the center well 4, as shown in Figure 2. The amount of extraction is controlled. This is because as the amount of sludge retained in the settling tank 2 increases, it becomes more difficult to manage the sludge. However, in conventional settling tanks of this type, even by controlling the amount of sludge as described above, it is still difficult to prevent the sludge from floating due to the denitrification reaction. When the aeration tank is operated under high conditions, or when the residence time in the aeration tank is long and a large amount of nitrate nitrogen is produced, a problem arises in that the quality of treated water deteriorates significantly due to sludge floating.

The present invention has been made in view of the above circumstances, and is an activated sludge treatment that can prevent sludge from being mixed into supernatant water due to denitrification inside a settling tank, and can therefore maintain good quality of treated water. The purpose of the present invention is to provide a method for separating activated sludge and an apparatus therefor.

The present invention will be explained in detail below.

The present invention detects the anaerobic state of the sludge layer inside the sedimentation tank when introducing the mixed solution after activated sludge treatment into the sedimentation tank and separates it by sedimentation, and based on this detection signal, the sedimentation tank A method for sedimentation separation in activated sludge treatment, characterized in that sludge is pulled out at a predetermined flow rate from the sludge and stored outside the settling tank, and the stored sludge is returned to the settling tank at a predetermined flow rate. In a sedimentation separator that separates the mixed liquid after activated sludge treatment into sludge and supernatant water, the mixed liquid is introduced into a settling tank, and the sludge is extracted from the sludge layer generated inside the settling tank and removed from the outside of the settling tank. a control means for detecting the anaerobic state of the sludge layer and controlling the amount of sludge transferred by the transfer means based on the detection signal; a sludge advection tank for storing the transferred sludge; This is a sedimentation separation device characterized by comprising a return means for returning sludge from the sludge advection tank to the settling tank.

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is a diagram showing an embodiment of the present invention.
In this figure, reference numeral 10 is a sedimentation tank, and a center well 11 is provided upright in the center of the sedimentation tank 10. Further, a mixed liquid pipe 12 for guiding the mixed liquid from an aeration tank (not shown) is drawn into the settling tank 10, and is installed so that a discharge port 12a of this pipe 12 faces upward and opens inside the center well 11. has been done.

In addition, a sludge advection tank 1 is located close to the settling tank 10.
3 and an intermediate tank 14 are installed. These sludge advection tank 13 and intermediate tank 14 are connected via an overflow weir 15. In this example, the overflow weir 15
is set at a position lower than the overflow weir 10a of the settling tank 10, so that the water level of the sludge advection tank 13 is kept lower than the water level of the settling tank 10.

Between the settling tank 10 and the sludge advection tank 13,
Sludge advection pipes 16, 16, 16 are installed to transfer the settled sludge in the settling tank 10 to the sludge advection tank 13. A motor-operated valve 17 whose opening degree can be adjusted is provided in the intermediate portion of each sludge transfer pipe 16.
Further, a funnel-shaped suction port 16a is provided at the end of each sludge transfer pipe 16 on the settling tank 10 side, and manual valves 18 and 19 are provided near both ends, respectively.
is provided. These manual valves 18, 19
is provided to fill the inside of the sludge transfer pipe 16 with water when starting up the separation device, and both manual valves 18, 1
After the intermediate portion of the sludge transfer pipe 16 is evacuated with the valve 9 closed, both manual valves 18 and 19 are opened to introduce water into the interior. The positions of the suction ports 16a of the sludge transfer pipe 16 are determined so as to be distributed approximately evenly within the sludge layer 3 of the settling tank 10, but in this example, they are located near the middle and bottom of the sludge layer 3. ing.

Furthermore, a return pipe 22 in which a return pump 20 and an electric valve 21 are interposed is installed between the intermediate tank 14 and the settling tank 10 . The end of the return pipe 22 on the sedimentation tank 10 side is located inside the center well 11. Further, the return pipe 22 is branched between the return pump 20 and the electric valve 21,
A sludge return pipe 23 to an aeration tank (not shown) is connected.

In addition, in this example, as a means for detecting that the inside of the sludge layer 3 of the settling tank 10 has changed to an anaerobic state, the oxidation-reduction potential is generally detected as the anaerobic state progresses.
Since ORP decreases, an oxidation-reduction potential detection element (ORP detection element) 25 is installed near the bottom of the settling tank 10, and the output of this ORP detection element 25 is input to an oxidation-reduction potentiometer (ORP meter) 26. It is becoming more and more common. And this ORP total 2
The output of 6 is input to a control device 27, and this control device 27 is adapted to adjust the opening degree of the electric valve 17 of the sludge advection pipe 13 and the electric valve 21 of the return pipe 22 according to the input signal. .

Next, the operating method and operation of the above-mentioned precipitation separator will be explained.

The mixed liquid that has undergone activated sludge treatment in the aeration tank is sent into the center well 11 through the mixed liquid pipe 12, descends within the center well 11, and is dispersed into the sludge layer 3 from the lower end opening. As this mixed liquid slowly rises within the sludge layer 3, the sludge in the mixed liquid is filtered into the sludge layer 3 until it becomes fine flocs due to the filter effect due to the synergistic effects of adsorption, adhesion, coagulation, etc. of the sludge layer 3. Captured.
The supernatant water from which the sludge has been removed overflows from the overflow weir 10a as treated water. During this sedimentation and separation operation, the upper part of the sludge layer 3 is always kept above the lower end opening of the center well 11.

In addition, the inside of the sludge layer 3 tends to become anaerobic due to lack of dissolved oxygen, but in this device, the sedimentation tank 10 has a flow rate corresponding to the degree of anaerobicity of the sludge layer 3.
and the sludge advection tank 13,
Suppresses the progress of anaerobism.

That is, in the above device, since the water level of the settling tank 10 is set higher than the water level of the sludge advection tank 13, the sludge layer is heated at a flow rate corresponding to the opening degree of the electric valve 17 of the sludge advection pipe 16 due to the difference in water heads. The sludge No. 3 is drawn out and sent to the sludge advection tank 13. At the same time, a part of the sludge that has overflowed from the sludge advection tank 13 to the intermediate tank 14 is transferred to the electric valve 2 by the return pump 20.
It is returned to the settling tank 10 at a flow rate according to the opening degree of 1,
A portion of the sludge is recycled. Here, the sludge flow rate is controlled by transmitting ORP data in the sludge layer 3 to the control device 2.
7, and each electric valve 17, 21 is controlled based on the PID operation set in advance by this control device 27.
Adjust the opening degree.

In addition, during the above-mentioned sludge circulation operation, the intermediate tank 14
A part of the returned sludge is returned to the aeration tank through the sludge return pipe 23 and is again subjected to activated sludge treatment.

Thus, in the above sedimentation separation operation, the settled sludge inside the settling tank 10 is maintained in a state of gentle movement inside the sludge layer 3. Therefore, the anaerobic portion inside the sludge layer 3 is removed and the denitrification reaction is suppressed. In addition, even if nitrogen gas is generated due to partial denitrification, the sludge is moving slowly, which promotes defoaming and prevents the formation of scum, thus preventing sludge from getting mixed into the supernatant water. Treated water quality is maintained in good condition. Furthermore, in the apparatus of the present invention, since the sludge layer 3 is effectively prevented from becoming anaerobic, it is possible to operate with an increased amount of retained sludge. By using the filter effect of the sludge layer, the sludge in the mixed liquid introduced can be captured down to the fine flocs, thereby improving the quality of treated water. In addition, since the sludge in the sludge layer can be caused to undergo continuous or intermittent gentle movement, it is possible to prevent the sludge from sticking to the inner wall surface, bottom, etc. of the settling tank 10. Concomitantly, since the angle of inclination inside the settling tank 10 can be set smaller than before, the effective capacity of the settling tank can be increased. Furthermore, along with preventing the sludge in the settling tank from becoming anaerobic, the sludge
Since the ORP is kept sufficiently high, the amount of phosphorus ingested by organisms in the sludge (normally ORP is 0 to -
(which elutes at 200 mV or less) is reliably prevented, thereby improving the dephosphorization rate.

Next, another embodiment of the present invention will be described with reference to FIG. In this figure, the same components as those in FIG. 3 are given the same reference numerals and their explanations will be omitted.

The sedimentation separator shown in FIG. 4 is different from the one shown in FIG. 12, hydrogen ion concentration detection elements 30 and 31 are provided. This means that when denitrification occurs inside the sludge layer, alkalinity increases by 3.57 mg per 1 mg of nitrogen.
This method takes advantage of the phenomenon in which the PH increases, and the PH of the mixture
The degree of anaerobicization of the sludge layer is detected based on the difference between the pH value in the sludge layer and the PH in the sludge layer, and the circulating flow rate of sludge is controlled based on this detected value. And the fourth
Similarly to the apparatus shown in FIG. 3, the apparatus shown in FIG. 3 can control the circulation of sludge so that anaerobic formation of the sludge layer does not progress, and the same effect can be obtained.

In addition, in the above embodiment, the sludge suction port 1
6a is provided at the lower part and middle part of the sediment layer 3, but the installation position of the suction port and its opening direction are as follows.
It is determined according to the size and shape of the settling tank to effectively prevent sludge from becoming anaerobic.

As described in detail above, the sedimentation separation method and apparatus of the present invention circulates sludge by advection and return between the sedimentation tank and the sludge advection tank, and the flow rate of the sludge is adjusted to the sludge layer. Since this is carried out based on the detection signal of the anaerobic state, the sludge in the settling tank can be prevented from becoming anaerobic and can be caused to move slowly as appropriate. For this reason, in the settling tank, the denitrification reaction that causes sludge to become anaerobic is suppressed, and the scum of the sludge due to nitrogen gas is prevented, so sludge does not get mixed into the treated water and the quality of the treated water is improved. It is maintained. Furthermore, even if nitrogen gas is generated due to denitrification in a part of the sludge, the sludge is moving slowly, which promotes defoaming and prevents the sludge from floating up. In addition, as mentioned above, sludge management becomes easier, making it possible to control the amount of retained sludge so that the lower end opening of the center well is located inside the sludge layer, which allows the mixed liquid to be introduced into the center well. When passing through the sludge layer, the filter effect of the sludge layer traps even the finest flocs, improving the quality of the treated water. Furthermore,
Since the sludge layer is prevented from becoming anaerobic, the phosphorus ingested by living organisms in the sludge is prevented from leaching out, resulting in effects such as being able to improve the phosphorus removal rate.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram for explaining the outline of conventional activated sludge treatment, Fig. 2 is a schematic configuration diagram of a conventional hopper-type sedimentation tank equipped with a center well, and Fig. 3 is an explanatory diagram for explaining the outline of conventional activated sludge treatment. FIG. 4 is a schematic diagram of one embodiment of the present invention. FIG. 4 is a schematic diagram of another embodiment of the present invention. 10... Sedimentation tank, 11... Center well, 1
2...Mixed liquid piping, 13...Sludge advection tank, 14...
...Middle layer, 16...Sludge advection pipe, 17...Electric valve, 20...Return pump, 21...Electric valve, 22
... Return pipe, 25 ... Redox potential detection element, 2
6... Oxidation-reduction potentiometer, 27... Control device, 3
0,31...Hydrogen ion concentration detection element.

Claims (1)

[Scope of Claims] 1. When introducing the mixed liquid after activated sludge treatment into a settling tank and separating it by sedimentation, detecting the anaerobic state of the sludge layer inside the settling tank, and based on this detection signal. Sedimentation in activated sludge treatment, characterized in that sludge is pulled out from the settling tank at a predetermined flow rate and stored outside the settling tank, and the stored sludge is returned to the settling tank at a predetermined flow rate. Separation method. 2. The settling tank includes a center well arranged such that a lower end opening is located inside the sludge layer, and the mixed liquid is introduced into the settling tank and the sludge is returned inside the center well. A precipitation separation method according to claim 1. 3. The anaerobic state of the sludge layer is detected based on the redox potential of the sludge layer, and the amount of sludge transferred is controlled based on the detected value of the redox potential. The precipitation separation method described in Section 2. 4. The anaerobic state of the sludge layer is detected based on a difference in hydrogen ion concentration between the liquid mixture and the sludge layer, and the amount of sludge transferred is controlled based on the difference in hydrogen ion concentration. Paragraph 1 or 2
Precipitation separation method described in section. 5 In a sedimentation separation device that separates the mixed liquid after activated sludge treatment into sludge and supernatant water, there is a settling tank into which the mixed liquid is introduced, and a settling tank where sludge is extracted from the sludge layer generated inside the settling tank and transferred to the outside of the settling tank. a control means for detecting the anaerobic state of the sludge layer and controlling the amount of sludge transferred by the transfer means based on the detection signal; a sludge advection tank for storing the transferred sludge; A sedimentation separation device comprising a return means for returning the sludge from the sludge transfer tank to the sedimentation tank. 6. The settling tank includes a center well arranged such that a lower end opening is located inside the sludge layer, and an inlet for the mixed liquid and an inlet for the returned sludge are opened inside the center well. A precipitation separator according to claim 5. 7. As a means for detecting the anaerobic state of the sludge layer,
7. The precipitation separation apparatus according to claim 5, further comprising an oxidation-reduction potential detection element located inside the precipitation tank. 8. The detection means for detecting the anaerobic state of the sludge layer is provided with a hydrogen ion concentration detection element that detects the hydrogen ion concentration of the mixed liquid and the hydrogen ion concentration inside the sludge layer, respectively. The precipitation separator according to item 5 or 6.