CN108114512B

CN108114512B - Method for inhibiting sludge bulking of secondary sedimentation tank

Info

Publication number: CN108114512B
Application number: CN201611072926.7A
Authority: CN
Inventors: 赵胜楠; 高会杰; 孙丹凤; 郭志华
Original assignee: China Petroleum and Chemical Corp; Sinopec Fushun Research Institute of Petroleum and Petrochemicals
Current assignee: China Petroleum and Chemical Corp; Sinopec Fushun Research Institute of Petroleum and Petrochemicals
Priority date: 2016-11-29
Filing date: 2016-11-29
Publication date: 2020-03-17
Anticipated expiration: 2036-11-29
Also published as: CN108114512A

Abstract

The invention relates to a method for inhibiting sludge expansion of a secondary sedimentation tank, wherein the secondary sedimentation tank adopts a form that water enters from bottom to top at the bottom and flows out from the periphery, a hollow cylindrical sleeve is arranged around a water inlet pipe, and the bottom end of the sleeve is a bell mouth; sewage discharged into the secondary sedimentation tank enters from the bottom of the tank, flows out from the periphery of the top of the water inlet pipe, downwards flows through a bell mouth of the sleeve, diffuses towards the upper part and the periphery of the outside of the sleeve, and is finally discharged from a water outlet at the top of the secondary sedimentation tank; when the sludge is expanded, the sleeve is used for preventing the expanded sludge from floating to the top and the edge of the secondary sedimentation tank; an inclined support frame is arranged on the periphery of the bottom end of the water inlet pipe, and an aeration system is arranged on the support frame and used for alternately aerating air and chlorine for inhibiting sludge expansion; and after the aeration is stopped, the settled sludge flows out from the bell mouth and is discharged through a sludge discharge pipe. According to the invention, by adopting the secondary sedimentation tank with an improved structure, the growth of zoogloea on the secondary sedimentation tank is promoted by using filamentous fungi as a framework while non-filamentous fungi and toxic substances are eliminated, the expansion and floating of sludge are effectively inhibited, and the clarity of the effluent is ensured.

Description

Method for inhibiting sludge bulking of secondary sedimentation tank

Technical Field

The invention belongs to the technical field of sewage treatment, and particularly relates to a method for inhibiting sludge bulking of a secondary sedimentation tank.

Background

The activated sludge process is a biological sewage treatment technology widely used in sewage treatment. The secondary sedimentation tank is an important component of an activated sludge system and mainly has the functions of separating sludge, clarifying mixed liquor, concentrating and refluxing activated sludge. The working effect can directly influence the effluent quality and the return sludge concentration of the activated sludge system. The secondary sedimentation tank of the large and medium-sized sewage treatment field adopts a circular radial flow type of mechanical mud suction, the medium-sized sewage treatment field also adopts a multi-bucket horizontal flow type, and the small-sized sewage treatment field adopts a vertical flow type.

The activated sludge settled in the secondary sedimentation tank is usually positioned at the bottom of the tank, and the dissolved oxygen concentration is low, so that sludge bulking is easy to occur. Sludge bulking can be generally divided into two broad categories, filamentous bulking and non-filamentous bulking. The filamentous bacterium bulking is caused by excessive propagation of filamentous bacteria in the activated sludge floc, and the non-filamentous bacterium bulking is caused by abnormal physiological activities of the zoogloea, massive production of viscous substances or the existence of toxic substances, so that the zoogloea cannot secrete the viscous substances and cannot flocculate and settle. The two sludge expansions usually exist at the same time, and both sludge can float to the surface of a secondary sedimentation tank, so that on one hand, the sludge-water separation effect is poor, the concentration of Suspended Substances (SS) in effluent exceeds the standard, on the other hand, the concentration and the quality of return sludge are reduced, the required normal sludge amount in an aeration tank is influenced, and great difficulty is brought to the operation and the control of sewage treatment. The common practice of sewage treatment plants is to kill filamentous and non-filamentous bacteria together by adding medicaments to prevent sludge bulking or increase the sludge return flow, and the effect is not ideal. As the filamentous fungi also have positive effects in sewage treatment, the filamentous fungi are skeletons for growth of zoogloea and have adsorption effects on organic matters, the expansion control by killing the filamentous fungi is insufficient, and the added medicament also has certain influence on the quality of effluent water to cause secondary pollution of the water quality.

CN201510138520.3 discloses a secondary sedimentation tank sludge floating early warning and control method of a sewage treatment system, which is characterized in that early warning classification for secondary sedimentation tank sludge floating in the sewage treatment system is established; dividing the secondary sedimentation tank into three stages according to the proportion of the floating sludge coverage area of the secondary sedimentation tank to the surface area of the tank body, namely the coverage, the ratio of black quantity to brown quantity in the activated sludge color and the number of filamentous microorganisms; and controlling by adopting a corresponding method according to early warning classification. The invention carries out early warning at the initial stage of sludge floating, adopts different countermeasures respectively to eliminate the sludge in the initial state, and can greatly reduce the probability of sludge floating. However, the method uses naked eyes to observe the proportion of the floating sludge coverage area of the secondary sedimentation tank to the surface area of the tank body and the proportion of black quantity and brown quantity in the activated sludge color, so that errors are easily caused, and the method is complex to implement, needs to continuously change process parameters such as reflux ratio and the like, and is not economical and practical.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a method for inhibiting the sludge bulking of a secondary sedimentation tank. According to the invention, by adopting the secondary sedimentation tank with an improved structure, the filamentous fungi are used as the framework to promote the growth of the zoogloea thereon while eliminating the non-filamentous fungi and toxic substances, the loss of the available part is avoided while eliminating the unavailable part, the expansion and floating of the sludge are effectively inhibited, and the clarity of the effluent is ensured.

The method for inhibiting the sludge bulking of the secondary sedimentation tank comprises the following steps: the secondary sedimentation tank adopts a form that water enters from bottom to top and flows out from the periphery, a hollow cylindrical sleeve is arranged around the vertical section of the water inlet pipe, and the bottom end of the sleeve is a bell mouth; sewage discharged into the secondary sedimentation tank enters from a water inlet pipe at the bottom of the tank, flows out from the periphery of the top of the water inlet pipe, downwards passes through a bell mouth of the sleeve, diffuses towards the outer upper part and the periphery of the sleeve, and is finally discharged from a water outlet at the top of the secondary sedimentation tank; when sludge expansion occurs, the sleeve is used for preventing the expanded sludge from floating to the top and the edge of the secondary sedimentation tank; an inclined support frame is arranged at the periphery of the bottom end of the water inlet pipe, and an aeration system is arranged on the support frame and used for alternately aerating air and chlorine for inhibiting sludge expansion; and after the aeration is stopped, the settled sludge flows out from the bell mouth of the sleeve and is discharged through a sludge discharge pipe below the support frame.

In the invention, the diameter of the sleeve is 1/6-1/4 of the diameter of the secondary sedimentation tank, the top end of the sleeve is 0.3-0.5m higher than the highest liquid level of the secondary sedimentation tank, and the vertical distance from the bottom end of the bell mouth to the lowest point of the bottom of the secondary sedimentation tank is 1/6-1/4 of the height of the secondary sedimentation tank. The included angle a between the bell mouth and the sleeve wall is 30-60 degrees, and the horizontal projection length is 1/6-1/5 of the radius of the secondary sedimentation tank. The bottom end of the sleeve is provided with a bell mouth, and the support frame and the aeration system are inclined downwards at a certain angle, so that sludge can be favorably settled to the bottom of the secondary sedimentation tank smoothly without influencing sludge discharge of the secondary sedimentation tank; meanwhile, the aeration lock is arranged in the sleeve, so that the disturbance to the sewage at the periphery of the sleeve is avoided.

In the invention, the support frames are continuously arranged or arranged at intervals around the water inlet pipe, and 3-8 support plates can be uniformly distributed at intervals. The included angle b between the support frame and the water inlet pipe wall is 30-60 degrees, the horizontal projection length of the support frame is 4/5-5/6 of the radius of the sleeve, and the vertical distance from the bottom end of the support frame to the lowest point of the bottom of the secondary sedimentation tank is 1/6-1/4 of the height of the secondary sedimentation tank.

In the invention, the support frame is provided with an aeration system which can be an annular aeration disc, and the inner wall of the aeration disc is fixedly connected with the wall of the water inlet pipe; or the circular aeration coil pipes are independent circular aeration coil pipes with different diameters, and the coil pipes are annularly arranged on the support frame for 2-8 circles.

In the invention, the dissolved oxygen meter is arranged in the sleeve to monitor and regulate the concentration of the dissolved oxygen in the sleeve on line. When the concentration of Dissolved Oxygen (DO) is continuously lower than 1mg/L, detecting the volume index SVI of the sludge in the pool, wherein the SVI is 80-150mg/L under the normal condition; and when the SVI is continuously higher than 150mg/L, starting an aeration system in the sleeve for aeration.

In the invention, the aeration mode adopts intermittent aeration, and two aerations and one aeration stop form a group. Chlorine is aerated for 10-20min, the aeration amount is controlled to be 5-10mg/L, and the concentration can kill toxic substances in the sludge without greatly influencing filamentous bacteria; then aerating air for 20-40min to realize a local aeration space in the sleeve, and controlling the Dissolved Oxygen (DO) at 2-5 mg/L; stopping aeration for 20-40 min. The toxic substances (non-filamentous bacteria expansion) in the expanded sludge can be killed by firstly aerating chlorine gas, and then aerating air, so that a local aeration space can be realized in the sleeve, and filamentous bacteria sludge expansion can be inhibited. Dissolved oxygen is an important factor affecting the expansion of filamentous fungi, most of aerobic fungi hardly continue to grow and propagate at a low DO value, and filamentous fungi continue to grow and propagate because of having long hyphae, a large specific surface area and a low oxygen saturation constant, and DO not lose viability even if they are in an anaerobic state for a long time. Therefore, the aeration can effectively inhibit the growth of filamentous fungi, promote the growth of zoogloea and prevent the zoogloea from flowing out of the secondary sedimentation tank along with water flow. Stopping aeration is mainly used for natural sedimentation of sludge, and the settled sludge flows out from the bell mouth and is discharged by a sludge discharge pipe. When the SVI is maintained at 80-150mg/L and the DO stabilizes at 2-5mg/L, the above operation is stopped.

In the invention, a feed inlet is arranged on the horizontal section of the water inlet pipeline, when the dissolved oxygen in the sleeve is continuously lower than 1mg/L, the SVI is continuously higher than 150mg/L, if B: N is more than 100:3, B: P is more than 100:0.5, (B: 5 daily biochemical oxygen demand BOD, N: total nitrogen and P: total phosphorus), a nitrogen source and a phosphorus source are supplemented into the sleeve, so that 100:5< B: N <100:3 and 100:1< B: P <100:0.5, and the sludge expansion is further effectively inhibited. The nitrogen source can be common nitrogen-containing compounds such as ammonium sulfate, and the phosphorus source can be common phosphorus-containing compounds such as potassium dihydrogen phosphate.

In the invention, the hydraulic retention time of the sewage is controlled to be 0.5-1.5 h.

Compared with the prior art, the invention has the following advantages:

1. the sleeve, the support frame and the aeration system are arranged around the water inlet pipe at the bottom of the secondary sedimentation tank, and the mode of alternately exposing chlorine and air is adopted, namely a biological selector is arranged in the tank, the zoogloea is selectively grown, meanwhile, the growth of filamentous fungi is inhibited, and on the premise of not changing the sewage treatment process, the growth of the filamentous fungi is effectively inhibited and controlled through simple structural improvement and operation, so that the loss of the filamentous fungi is avoided, and the clarity of the outlet water is effectively ensured.

2. The aeration mode adopts a mode of two-aeration one-stop, fine sludge floats in the aeration stage, the fine sludge is prevented from flowing out along with water flow, most filamentous bacteria are kept as a framework to promote the growth of zooglea by adopting a mode of firstly aerating chlorine and then aerating air, the growth efficiency of the zooglea can be effectively improved, meanwhile, the time for continuous sedimentation of the zooglea is given, and the clarity of effluent is improved.

3. The invention controls the sludge expansion of the secondary sedimentation tank in multiple aspects of aeration mode, dissolved oxygen, nitrogen and phosphorus nutrient substances and the like, and respectively treats the expansion of filamentous bacteria and non-filamentous bacteria, thereby not only inhibiting the occurrence of viscous expansion, but also keeping the function of the filamentous bacteria as a zoogloea framework, thoroughly solving the problem of sludge expansion, and having simple and practical device structure and flexible operation.

Drawings

FIG. 1 is a schematic structural view of a secondary sedimentation tank with an improved structure according to the present invention;

wherein, 1-water inlet pipe, 2-feed inlet, 3-sleeve, 4-support frame; 5-aeration pipe, 6-settling sludge, 7-sludge discharge pipe, 8-water outlet and 9-secondary settling tank wall.

FIG. 2 is a schematic top view of the secondary sedimentation tank with an improved structure of the present invention.

Detailed Description

The method and effect of the present invention will be described in detail below with reference to the accompanying drawings and examples. But are not to be construed as limiting the invention.

The specific structure of the secondary sedimentation tank with the improved structure is shown in figure 1, the form that water enters from bottom to top at the bottom and flows out from the periphery is adopted, a feed inlet 2 is arranged on a water inlet pipe 1, a hollow cylindrical sleeve 3 is arranged on the periphery of the water inlet pipe, and the bottom end of the sleeve is a bell mouth. When sludge bulking occurs, the sleeve serves to prevent the bulking sludge from floating towards the edge of the secondary sedimentation tank. An inclined support frame 4 is arranged at the periphery of the bottom end of the water inlet pipe, and an aeration pipe 5 is arranged on the support frame. When the aeration is started, alternately aerating air and chlorine; when chlorine is aerated, the method is used for eliminating non-filamentous bacteria and toxic substances in the expanded sludge; when the sleeve is aerated, a local aeration space is realized inside the sleeve, which is used for inhibiting the overgrowth of the filamentous fungi and promoting the growth of zoogloea. After the aeration is stopped, the settled sludge 6 flows out from the bell mouth of the sleeve and is discharged through a sludge discharge pipe 7 below the supporting frame.

The sewage adopted by the invention is sewage of a secondary sedimentation tank of a sewage treatment plant A, the ammonia nitrogen concentration in the sewage is less than 5mg/L, the total nitrogen concentration is less than 25mg/L, the sludge concentration is 2000mg/L, the dissolved oxygen concentration in the sleeve detected by an oxygen dissolving instrument is 2mg/L, and the SVI measured by taking a water sample is 120 mg/L. The nitrogen source adopts ammonium sulfate, and the phosphorus source adopts potassium dihydrogen phosphate.

Example 1

The height of the secondary sedimentation tank adopted in the embodiment is 0.5m, and the diameter is 1 m. The diameter of the sleeve is 0.18m, the top end of the sleeve is 0.4m higher than the liquid level of the secondary sedimentation tank, the included angle a between the bell mouth and the wall of the water inlet pipe is 60 degrees, the horizontal projection length of the bell mouth is 0.085m, and the vertical distance from the bottom end of the bell mouth to the bottom of the secondary sedimentation tank is 0.1 m. 4 support frames are arranged around the water inlet pipe at intervals, the included angle b between each support frame and the wall of the water inlet pipe is 60 degrees, the horizontal projection length of each support frame is 0.072m, and the distance from the bottom end of each support frame to the bottom of the secondary sedimentation tank is 0.1 m. Two circles of aeration coil pipes are fixed on the supporting frame. And a dissolved oxygen meter is arranged in the sleeve to monitor and regulate the concentration of dissolved oxygen in the sleeve on line.

The sewage with expanded sludge is generated in a secondary sedimentation tank of a sewage treatment plant, the SVI of the sewage is 250mg/L, and the retention time of the sewage is 0.5 h. The sewage enters a secondary sedimentation tank with an improved structure through a water inlet pipe, dissolved oxygen in a sleeve begins to fall after 5min, the concentration of the dissolved oxygen is lower than 1mg/L after 15min, the dissolved oxygen is continuously lower than 1mg/L after 20min, filamentous sludge floating in the sleeve can be seen by naked eyes, meanwhile, flocculent sludge is bonded, the sewage in the sleeve is sampled at the moment, the SVI value is measured to be 200mg/L, the sampling is carried out again after 10min, and the SVI value is 280 mg/L. At the moment, aeration is started, chlorine is aerated for 10min, dispersed sludge rises along with bubbles, then air aeration is carried out for 30min, dissolved oxygen is controlled to be 3mg/L, and then aeration is stopped for 20 min. The two groups are repeated, when the fourth group stops aeration, the density of bacterial micelles on the surfaces of the filamentous fungi is seen to be increased, the sludge has a settlement trend, the dissolved oxygen concentration in the sleeve is 1.5mg/L, the sewage SVI value is 200mg/L, when the fifth group stops aeration, the visible sludge part starts to agglomerate and settle, the dissolved oxygen concentration in the sleeve is 1.8mg/L, the sewage SVI value is 160mg/L, when the sixth group stops aeration, the sludge settlement is obvious, the dissolved oxygen concentration in the sleeve is 2.2mg/L, the sewage SVI value is 140mg/L, when the seventh group stops aeration, the sludge settlement is obvious, the dissolved oxygen concentration in the sleeve is stabilized at about 2.5mg/L, and the sewage SVI value is 120 mg/L. In the treatment process, the filamentous fungi hardly flow out of the secondary sedimentation tank along with sewage, and the effluent of the secondary sedimentation tank is clear. The returned sludge is yellow brown, the sludge quality is good, the aeration tank runs stably after entering the aeration tank, and the treatment effect is good.

Example 2

The procedure and operating conditions were the same as in example 1. The difference lies in that: when the SVI value is determined to be 200mg/L and sampled again after 10min for measurement, and the SVI value is 280mg/L, the sewage B: N =100:3 and B: P =100:0.3 in the sleeve are supplemented with monopotassium phosphate to ensure that B: P =100: 0.6. At this time, the aeration system is opened, and after 6 groups are repeated, the dissolved oxygen concentration in the sleeve is stabilized to be about 2.5mg/L, and the SVI value of the sewage is 120 mg/L. Compared with the example 1, the treatment effect is better, the treatment effect is also improved, and the number of aeration groups can be reduced.

Example 3

The height of the secondary sedimentation tank adopted in the embodiment is 0.5m, and the diameter is 1 m. The diameter of the sleeve is 0.25m, the top end of the sleeve is 0.3m higher than the liquid level of the secondary sedimentation tank, the included angle a between the bell mouth and the wall of the water inlet pipe is 30 degrees, the horizontal projection length of the bell mouth is 0.1m, and the vertical distance between the bottom end of the bell mouth and the bottom of the secondary sedimentation tank is 0.12 m. 4 support frames are arranged at the periphery of the water inlet pipe at intervals, the included angle b between each support frame and the wall of the water inlet pipe is 30 degrees, the horizontal projection length of each support frame is 0.08m, and the distance from the bottom end of each support frame to the bottom of the secondary sedimentation tank is 0.12 m. Two circles of aeration coil pipes are fixed on the supporting frame. And a dissolved oxygen meter is arranged in the sleeve to monitor and regulate the concentration of dissolved oxygen in the sleeve on line.

The sewage with expanded sludge is generated in a secondary sedimentation tank of a sewage treatment plant, the SVI of the sewage is 400mg/L, and the retention time of the sewage is 1.5 h. The sewage enters a secondary sedimentation tank with an improved structure through a water inlet pipe, dissolved oxygen in a sleeve begins to decline after 5min, the concentration of the dissolved oxygen is lower than 1mg/L after 15min, the dissolved oxygen is continuously lower than 1mg/L after 20min, filamentous sludge floating in the sleeve can be seen by naked eyes, meanwhile, flocculent sludge is bonded, the sewage in the sleeve is sampled at the moment, the SVI value is determined to be 300mg/L, the sampling is carried out again after 10min, and the SVI value is 380 mg/L. At the moment, aeration is started, chlorine gas is aerated for 20min, dispersed sludge rises along with bubbles, then air aeration is carried out for 40min, dissolved oxygen is controlled to be 3mg/L, and then aeration is stopped for 30 min. Repeating the two groups, wherein when the fourth group stops aeration, the density of bacterial micelles on the surfaces of the visible filamentous fungi is increased, sludge flocs are dispersed, the viscosity of sewage is reduced, and the sludge has a settlement trend, at the moment, the dissolved oxygen concentration in the sleeve is 1.8mg/L, the SVI value of the sewage is 250mg/L, when the fifth group stops aeration, the visible sludge part starts to agglomerate and settle, at the moment, the dissolved oxygen concentration in the sleeve is 2mg/L, the SVI value of the sewage is 200mg/L, when the sixth group stops aeration, the sludge settlement is obvious, at the moment, the dissolved oxygen concentration in the sleeve is 2.2mg/L, the SVI value of the sewage is 170mg/L, when the seventh group stops aeration, the sludge settlement is obvious, at the moment, the dissolved oxygen concentration in the sleeve is stabilized at about 2.5mg/L, and the SVI value of the. When the aeration of the eighth group is stopped, the dissolved oxygen concentration in the sleeve is stabilized at about 2.5mg/L, and the SVI value of the sewage is 130 mg/L. In the treatment process, the filamentous fungi hardly flow out of the secondary sedimentation tank along with sewage, and the effluent of the secondary sedimentation tank is clear. The returned sludge is yellow brown, the sludge quality is good, the aeration tank runs stably after entering the aeration tank, and the treatment effect is good.

Example 4

The procedure and operating conditions were the same as in example 3. The difference lies in that: when the SVI value is determined to be 300mg/L and sampled again after 10min for measurement, and the SVI value is 380mg/L, the sewage B: N =100:2 and B: P =100:0.3 in the sleeve are supplemented with ammonium sulfate and potassium dihydrogen phosphate to ensure that B: N =100:4 and B: P =100: 0.6. At this time, the aeration system is opened, and after 7 groups are repeated, the dissolved oxygen concentration in the sleeve is stabilized to be about 2.5mg/L, and the SVI value of the sewage is 120 mg/L. Compared with the example 3, the treatment effect is better, the treatment effect is also improved, and the number of aeration groups can be reduced.

Comparative example 1

The procedure and operating conditions were the same as in example 1. The difference lies in that: the adopted secondary sedimentation tank is not provided with a sleeve structure. And sewage enters the secondary sedimentation tank from the water inlet pipe, and the retention time of the sewage is 1 h. And after 5min, the dissolved oxygen in the sleeve begins to drop, the concentration of the dissolved oxygen is lower than 1mg/L after 20min, the concentration of the dissolved oxygen is continuously lower than 1mg/L after 30min, flocculent sludge can be seen by naked eyes to be continuously dense and spread to the edge of a secondary sedimentation tank, the sewage in the middle of the secondary sedimentation tank is sampled at the moment, the SVI value is determined to be 200mg/L, and the sampling is carried out again after 10min for measurement, wherein the SVI value is 300 mg/L. At this time, the aeration system was turned on, and the same operation as in example 1 was performed. Because of the barrier effect of the sleeve, filamentous fungi and flocculent sludge continuously diffuse around, the dissolved oxygen in the secondary sedimentation tank is continuously increased due to aeration, the secondary sedimentation tank runs disorderly, and the effluent is turbid.

Comparative example 2

The procedure and operating conditions were the same as in example 1. The difference lies in that: only air was exposed. Due to the interception of the sleeve to the expanded sludge, the effluent of the secondary sedimentation tank is clear temporarily, but due to the absence of the synergistic effect of the aeration system, the effect of inhibiting the growth of filamentous bacteria is lost, the dissolved oxygen of the sewage in the sleeve is continuously reduced, the sludge is subjected to denitrification, bubbles are generated, the sludge is subjected to floating, and the effluent of the secondary sedimentation tank is turbid.

Comparative example 3

The procedure and operating conditions were the same as in example 1. The difference lies in that: only chlorine gas was aerated. Due to the interception of the sleeve to the expanded sludge, the effluent of the secondary sedimentation tank is clear temporarily, but due to the absence of the synergistic effect of the aeration system, the effect of inhibiting the growth of filamentous bacteria is lost, the dissolved oxygen of the sewage in the sleeve is continuously reduced, the sludge is subjected to denitrification, bubbles are generated, the sludge is subjected to floating, and the effluent of the secondary sedimentation tank is turbid.

Claims

1. A method for inhibiting sludge bulking in a secondary sedimentation tank is characterized by comprising the following steps: the secondary sedimentation tank adopts a form that water enters from bottom to top and flows out from the periphery, a hollow cylindrical sleeve is arranged around the vertical section of the water inlet pipe, and the bottom end of the sleeve is a bell mouth; sewage discharged into the secondary sedimentation tank enters from a water inlet pipe at the bottom of the tank, flows out from the periphery of the top of the water inlet pipe, downwards passes through a bell mouth of the sleeve, diffuses towards the outer upper part and the periphery of the sleeve, and is finally discharged from a water outlet at the top of the secondary sedimentation tank; when sludge expansion occurs, the sleeve is used for preventing the expanded sludge from floating to the top and the edge of the secondary sedimentation tank; an inclined support frame is arranged at the periphery of the bottom end of the water inlet pipe, and an aeration system is arranged on the support frame and used for alternately aerating air and chlorine for inhibiting sludge expansion; and after the aeration is stopped, the settled sludge flows out from the bell mouth of the sleeve and is discharged through a sludge discharge pipe below the support frame.

2. The method of claim 1, wherein: the diameter of the sleeve is 1/6-1/4 of the diameter of the secondary sedimentation tank, the top end of the sleeve is 0.3-0.5m higher than the highest liquid level of the secondary sedimentation tank, and the vertical distance from the bottom end of the bell mouth to the bottom of the secondary sedimentation tank is 1/6-1/4 of the height of the secondary sedimentation tank.

3. The method according to claim 1 or 2, characterized in that: the included angle a between the bell mouth and the sleeve wall is 30-60 degrees, and the horizontal projection length is 1/6-1/5 of the radius of the secondary sedimentation tank.

4. The method of claim 1, wherein: the support frame is arranged around the water inlet pipe continuously or at intervals, and 3-8 support plates can be uniformly distributed at intervals.

5. The method according to claim 1 or 4, characterized in that: the included angle b between the support frame and the water inlet pipe wall is 30-60 degrees, the horizontal projection length of the support frame is 4/5-5/6 of the radius of the sleeve, and the vertical distance from the bottom end of the support frame to the bottom of the secondary sedimentation tank is 1/6-1/4 of the height of the secondary sedimentation tank.

6. The method according to claim 1 or 4, characterized in that: the aeration system arranged on the supporting frame is an annular aeration disc; or the aeration coil pipe is an independent circular aeration coil pipe with different diameters, is sleeved on the water inlet pipe, and is arranged for 2-8 circles.

7. The method of claim 1, wherein: arranging a dissolved oxygen instrument in the sleeve, and carrying out online monitoring and regulation on the concentration of dissolved oxygen in the sleeve; when the concentration of the dissolved oxygen is continuously lower than 1mg/L, detecting the sludge volume index SVI in the pool, wherein the SVI is 80-150mg/L under the normal condition; and when the SVI is continuously higher than 150mg/L, starting an aeration system in the sleeve for aeration.

8. The method of claim 1, wherein: the aeration mode adopts intermittent aeration, and two aerations and one aeration stop form a group; firstly, chlorine is aerated for 10-20min, and the aeration amount is controlled to be 5-10 mg/L; then aerating air for 20-40min to realize a local aeration space in the sleeve, and controlling the dissolved oxygen to be 2-5 mg/L; stopping aeration for 20-40 min.

9. The method of claim 1, wherein: when the SVI is maintained at 80-150mg/L and the DO stabilizes at 2-5mg/L, aeration is stopped.

10. The method of claim 1, wherein: and a feed inlet is arranged on the horizontal section of the water inlet pipeline, when the dissolved oxygen in the sleeve is continuously lower than 1mg/L, the SVI is continuously higher than 150mg/L, if B: N is more than 100:3 and B: P is more than 100:0.5, a nitrogen source and a phosphorus source are supplemented into the sleeve, so that the ratio of 100:5 to B: N is less than 100:3, and the ratio of 100:1 to B: P is less than 100: 0.5.

11. The method of claim 10, wherein: the nitrogen source is ammonium sulfate, and the phosphorus source is potassium dihydrogen phosphate.

12. The method of claim 1, wherein: controlling the hydraulic retention time of the water entering the secondary sedimentation tank to be 0.5-1.5 h.