Two-stage AO circulation clarifier sewage treatment system

Abstract

The utility model discloses a two-stage AO circulation clarifier sewage treatment system, and relates to the technical field of water pollution control and treatment. The sewage treatment system comprises a biological tank and a nitrification liquid backflow facility, wherein the biological tank comprises a first-stage anoxic zone, a first-stage aerobic zone, a second-stage anoxic zone, a second-stage anaerobic zone and a second-stage aerobic and settling zone which are connected in sequence; and the first-stage anoxic zone is connected with the second-stage aerobic and settling zone through a nitrification liquid backflow facility. The two-stage AO circulation clarifier sewage treatment system provided by the utility model has the following advantages: (1) a carbon source in raw water is flexibly adjusted to different functional areas, so that the carbon source is fully utilized; (2) nitrification liquid sludge in the first-stage aerobic zone completely enters the second-stage anoxic zone, so that the denitrification capacity is higher; (3) the energy consumption of an internal reflux system is saved; (4) the sludge concentration of the first-stage anoxic zone and the second-stage anaerobic zone is higher, and nitrogen and phosphorus removal is more facilitated; and (5) the microorganisms enter an aerobic environment after releasing phosphorus, so that the biological phosphorus removal effect can be improved.

Description

Technical Field

[0001] The utility model relates to the technical field of water pollution control and treatment, in particular to a two-stage AO circulating clarifier sewage treatment system. Background Art

[0002] Conventional A 2 / RPIR pool uses a modified A 2 / O process——A 2 / RPIR, usually divided into three functional areas - anaerobic area (tank), anoxic area (tank) and RPIR area (tank), sewage undergoes anaerobic, anoxic and aerobic reactions in turn. 2 / The RPIR process has some process improvement needs: 1. The functional area is single, the raw water distribution ratio is difficult to adjust, and the carbon source is not maximized; 2. The sludge concentration in the anoxic zone is guaranteed by internal reflow measures, and the room for increasing the sludge concentration is limited. The denitrification capacity depends on the nitrification liquid sludge reflow ratio, and the energy consumption is relatively high; 3. The sludge concentration in the anaerobic zone also needs to be guaranteed by internal reflow measures. Its sludge concentration is the lowest among the three, which is not conducive to biological phosphorus removal; 4. The anaerobic zone is pre-placed, and then it goes through anoxic conditions to reach aerobic conditions, and the phosphorus release is insufficient.

[0003] Therefore, for conventional A 2 In view of the low concentration of anaerobic and anoxic sludge in the RPIR process, the carbon source of the raw water is not fully utilized, and the room for improving the efficiency of nitrogen removal and phosphorus removal is limited, a two-stage AO circulating clarifier sewage treatment system is provided. Utility Model Content

[0004] In order to solve the above technical problems, the utility model aims to propose a two-stage AO (AO: anoxic and aerobic) circulating clarifier sewage treatment system. By increasing the sludge concentration in the anaerobic zone and the anoxic zone, flexibly adjusting the proportion of raw water entering the anoxic zone and the anaerobic zone, reducing the power consumption of the nitrification liquid sludge return, and improving the denitrification and phosphorus removal capacity without deliberately increasing the effective volume of the tank body. The purpose of the utility model is achieved through the following technical solutions:

[0005] Provided is a two-stage AO circulating clarifier sewage treatment system, comprising a biological pool and a nitrification liquid return facility, wherein the biological pool comprises a first-stage anoxic zone, a first-stage aerobic zone, a second-stage anoxic zone, a second-stage anaerobic zone and a second-stage aerobic and sedimentation zone connected in sequence; the first-stage anoxic zone and the second-stage aerobic and sedimentation zone are connected via the nitrification liquid return facility.

[0006] Among them, the sewage in the biological pool undergoes alternating anoxic and aerobic conditions, with anaerobic conditions placed after anoxic conditions. The sewage then undergoes anoxic-aerobic-anoxic-anaerobic-aerobic reactions in sequence.

[0007] Among them, the relationship between the sludge size and concentration in the biological pond is: the second-level aerobic and sedimentation zone > the first-level anoxic zone = the first-level aerobic zone > the second-level anoxic zone, the second-level anaerobic zone.

[0008] Furthermore, the two-stage AO circulating clarifier sewage treatment system also includes a water distribution channel, the first-stage anoxic zone is provided with a first water distribution hole, and the second-stage anoxic zone is provided with a second water distribution hole; the first-stage anoxic zone is connected to the water distribution channel through the first water distribution hole, and the second-stage anoxic zone is connected to the water distribution channel through the second water distribution hole.

[0009] Furthermore, the second-stage anaerobic zone is provided with a third water distribution hole, and the second-stage anaerobic zone is connected to the water distribution channel through the third water distribution hole.

[0010] Furthermore, a circulating clarifier module is provided in the second-stage aerobic and sedimentation zone.

[0011] Among them, the mud and water separation function is only set in the second-level aerobic and sedimentation area. A circulating clarifier module is set in this area, and the mud and water separation is achieved through the circulating clarifier module and the clean water is discharged.

[0012] Furthermore, the nitrification liquid reflux facility includes a reflux channel and a reflux pump well, the reflux channel is arranged between the second-stage aerobic and sedimentation zone and the first-stage anoxic zone, and the reflux pump well is arranged between the reflux channel and the second-stage aerobic and sedimentation zone.

[0013] Furthermore, the nitrification liquid reflux facility also includes a reflux pump, and the reflux pump is arranged between the reflux channel and the reflux pump well.

[0014] Among them, the biological pool has only one nitrification liquid internal reflow facility, which lifts the nitrification liquid sludge from the second-level aerobic and sedimentation areas to the first-level anoxic zone for denitrification reaction. The first-level anoxic zone, the first-level aerobic zone, the second-level anoxic zone, and the second-level anaerobic zone all rely on the internal reflow facility to supplement the sludge concentration.

[0015] Furthermore, a decreasing aeration zone is provided at one end of the first-stage aerobic zone close to the second-stage anoxic zone.

[0016] Among them, all the nitrified liquid sludge in the first-level aerobic zone enters the second-level anoxic zone, and the gradually decreasing aeration zone ensures that the anoxic environment of the second-level anoxic zone is maintained.

[0017] Furthermore, the two-stage AO circulating clarifier sewage treatment system also includes a sludge pre-concentration zone, and the sludge pre-concentration zone is connected to a return pump well or a return channel.

[0018] Wherein, the sludge pre-concentration zone is intended to concentrate the excess sludge in the biological pool.

[0019] Furthermore, a first sludge lifting pump is provided in the reflux pump well or reflux channel, the sludge pre-concentration zone is connected to the reflux pump well or reflux channel via the first sludge lifting pump, and a second sludge lifting pump is provided in the sludge pre-concentration zone.

[0020] Preferably, the sludge pre-concentration zone is connected to the return channel, a first sludge lifting pump is provided in the return channel, and the sludge pre-concentration zone is connected to the return channel through the first sludge lifting pump.

[0021] The first sludge lifting pump lifts the sludge to the sludge pre-concentration area. After the sludge is concentrated in this area, it is discharged from the biological pool through the second sludge lifting pump.

[0022] Preferably, the sludge pre-concentration zone is connected to a reflux pump well, a first sludge lifting pump is provided in the reflux pump well, and the sludge pre-concentration zone is connected to the reflux pump well through the first sludge lifting pump.

[0023] Furthermore, the sludge pre-concentration zone is connected to the second-stage anoxic zone, the second-stage anaerobic zone or the second-stage aerobic and sedimentation zone through a connecting channel, and the connecting channel is a flow hole or a pipeline.

[0024] The supernatant in the sludge pre-concentration zone flows into the second-stage anoxic zone, the second-stage anaerobic zone or the second-stage aerobic and sedimentation zone through a connecting channel.

[0025] Among them, the technical implementation idea of ​​the utility model is: ① The biological pool needs to be set up with five functional areas, the first-level anoxic area, the first-level aerobic area, the second-level anoxic area, the second-level anaerobic area, the second-level aerobic and sedimentation area; ② The circulating clarifier module is only installed in the second-level aerobic and sedimentation area; ③ The raw water is mainly distributed in equal proportion to enter the first-level anoxic area and the second-level anoxic area, and part of the raw water is reserved to enter the second-level anaerobic area; ④ A nitrification liquid reflux facility is set up; ⑤ A sludge pre-concentration area is set up to gravity concentrate the remaining sludge before discharging it.

[0026] The beneficial effects compared with the prior art are:

[0027] (1) In the two-stage AO circulating clarifier sewage treatment system of the utility model, the nitrified liquid sludge in the first-stage aerobic zone can all flow into the second-stage anoxic zone without internal reflux measures, so that it can contact with the carbon source in the raw water more fully and denitrification is more thorough.

[0028] (2) The two-stage AO circulating clarifier sewage treatment system of the utility model divides the raw water into two equal parts, is easy to operate, and meets the carbon source requirements of the first-stage anoxic zone and the second-stage anoxic zone.

[0029] (3) The two-stage AO circulating clarifier sewage treatment system of the utility model can increase the sludge concentration in the first-stage anoxic zone and the second-stage anaerobic zone without deliberately increasing the reflow ratio, and the increase in microorganisms is more beneficial to nitrogen and phosphorus removal.

[0030] (4) The two-stage AO circulating clarifier sewage treatment system of the utility model is provided with five functional zones, and the microorganisms alternate between the deficient, good and anaerobic environments, especially immediately entering the aerobic environment after the anaerobic environment, and the phosphorus absorption power is utilized in time. This "starvation effect" can improve the effect of biological phosphorus removal.

[0031] (5) The two-stage AO circulating clarifier sewage treatment system of the utility model is provided with a sludge pre-concentration zone, where the concentration of the residual sludge to be discharged can be concentrated and precipitated by gravity, thereby reducing the volume of the residual sludge discharged. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the utility model, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 A plan view of a two-stage AO circulating clarifier sewage treatment system provided by an embodiment of the utility model;

[0034] Figure 2 A working relationship diagram of the inlet and outlet water volume and sludge concentration of a two-stage AO circulating clarifier sewage treatment system provided in an embodiment of the utility model.

[0035] Description of the symbols in the figure:

[0036] 01-first-stage anoxic zone; 02-first-stage aerobic zone; 03-second-stage anoxic zone; 04-second-stage anaerobic zone; 05-second-stage aerobic and sedimentation zone; 10-water distribution channel; 11-first water distribution hole; 12-second water distribution hole; 13-third water distribution hole; 20-return pump well; 21-return channel; 22-return pump; 30-sludge pre-concentration zone; 31-first sludge lifting pump; 32-second sludge lifting pump; 40-circulation clarifier module. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0038] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0039] It should also be understood that the terms used in this utility model specification are only for the purpose of describing specific embodiments and are not intended to limit the utility model. As used in this utility model specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0040] It should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are the directions or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0041] The terms "parallel", "vertical", etc. do not mean that the components must be absolutely parallel or vertical, but can be slightly tilted. For example, "parallel" only means that its direction is more parallel than "vertical", and does not mean that the structure must be completely parallel, but can be slightly tilted.

[0042] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] Example

[0044] The utility model provides a two-stage AO circulating clarifier sewage treatment system, which aims to increase the sludge concentration in anaerobic and anoxic zones, flexibly adjust the proportion of raw water entering the anoxic and anaerobic zones, reduce the power consumption of nitrification liquid sludge backflow, and improve the denitrification and phosphorus removal capabilities without deliberately increasing the effective volume of the pool body.

[0045] See also Figure 1-Figure 2 The two-stage AO circulation clarifier sewage treatment system shown includes a biological pool and a nitrification liquid return facility. The biological pool includes a first-stage anoxic zone 01, a first-stage aerobic zone 02, a second-stage anoxic zone 03, a second-stage anaerobic zone 04 and a second-stage aerobic and sedimentation zone 05 connected in sequence; the first-stage anoxic zone 01 and the second-stage aerobic and sedimentation zone 05 are connected through a nitrification liquid return facility. It also includes a water distribution channel 10, the first-stage anoxic zone 01 is provided with a first water distribution hole 11, and the second-stage anoxic zone 03 is provided with a second water distribution hole 12; the first-stage anoxic zone 01 is connected to the water distribution channel 10 through the first water distribution hole 11, and the second-stage anoxic zone 03 is connected to the water distribution channel 10 through the second water distribution hole 12. The second-stage anaerobic zone 04 is provided with a third water distribution hole 13, and the second-stage anaerobic zone 04 is connected to the water distribution channel 10 through the third water distribution hole 13. The water distribution channel 10 can adjust the water inflow flow. The water distribution channel 10, the first water distribution hole 11, the second water distribution hole 12, and the third water distribution hole 13 are all water distribution facilities. A decreasing aeration zone is provided at one end of the first-stage aerobic zone 02 close to the second-stage anoxic zone 03. A circulating clarifier module 40 is provided in the second-stage aerobic and sedimentation zone 05. The nitrification liquid return facility includes a return channel 21 and a return pump well 20. The return channel 21 is arranged between the second-stage aerobic and sedimentation zone 05 and the first-stage anoxic zone 01, and the return pump well 20 is arranged between the return channel 21 and the second-stage aerobic and sedimentation zone 05. The nitrification liquid return facility also includes a return pump 22, and the return pump 22 is arranged between the return channel 21 and the return pump well 20. It also includes a sludge pre-concentration zone 30, and the sludge pre-concentration zone 30 is connected to the return channel 21. A first sludge lifting pump 31 is provided in the return channel 21. The sludge pre-concentration zone 30 is connected to the return channel 21 through a first sludge lifting pump 31, and a second sludge lifting pump 32 is also provided in the sludge pre-concentration zone 30. The sludge pre-concentration zone 30, the first sludge lifting pump 31, and the second sludge lifting pump 32 are all one of the sludge pre-concentration facilities. The sludge pre-concentration zone 30 is connected to the second-stage anoxic zone 03, the second-stage anaerobic zone 04, or the second-stage aerobic and sedimentation zone 05 through a connecting channel, and the connecting channel is a flow hole or a pipeline. In this embodiment, the connecting channel is a flow hole, and the supernatant in the sludge pre-concentration zone 30 flows into the second-stage anoxic zone 03 or the second-stage anaerobic zone 04 through a pipeline.

[0046] Sewage (raw water) first enters the water distribution channel 10, which regulates the water flow to the first-level anoxic zone 01, the second-level anoxic zone 03, and the second-level anaerobic zone 04. The water distribution function of the water distribution channel 10 enables the raw water to enter the first-level anoxic zone 01, the second-level anoxic zone 03, and the second-level anaerobic zone 04. The sewage after the flow is regulated enters the first-level anoxic zone 01 through the first water distribution hole 11, enters the second-level anoxic zone 03 through the second water distribution hole 12, and enters the second-level anaerobic zone 04 through the third water distribution hole 13. In this embodiment, when the raw water is Q, half of the sewage (0.5Q) enters the first anoxic zone 01 through the first water distribution hole 11, and the other half of the sewage (0.5Q) enters the second anoxic zone 03 through the second water distribution hole 12. At the same time, the third water distribution hole 13 is retained, and a part of the sewage (satisfying 0-0.5Q) can be allocated according to the actual situation to enter the second anaerobic zone 04 to meet the demand for carbon source for anaerobic phosphorus release. The sewage passes through the first anoxic zone 01, the first aerobic zone 02, the second anoxic zone 03, the second anaerobic zone 04 and the second aerobic and sedimentation zone 05 in sequence to undergo anoxic, aerobic, anoxic, anaerobic, and aerobic reactions respectively. Among them, since the nitrified liquid sludge of the first-stage aerobic zone 02 all enters the second-stage anoxic zone 03, a decreasing aeration zone is provided at one end of the first-stage aerobic zone 02 close to the second-stage anoxic zone 03, and the decreasing aeration zone can reduce the dissolved oxygen to below 0.3 mg / L, thereby ensuring that the anoxic environment of the second-stage anoxic zone 03 is maintained. The circulation clarifier module 40 is only arranged in the second-stage aerobic and sedimentation zone 05, and the circulation clarifier module 40 has a mud-water separation function, and the circulation clarifier module 40 realizes mud-water separation and discharges clean water.

[0047] The nitrified liquid sludge of the second-stage aerobic and sedimentation tank 05 is collected in the return pump well 20. The return pump 22 is arranged between the return channel 21 and the return pump well 20. The nitrified liquid sludge in the return pump well 20 is lifted to the return channel 21 by the return pump 22, and then led to the first-stage anoxic zone 01 through the return channel 21. Among them, the biological pool has only one nitrified liquid internal return facility, which lifts the nitrified liquid sludge of the second-stage aerobic and sedimentation zone 05 to the first-stage anoxic zone 01 for denitrification reaction. The first-stage anoxic zone 01, the first-stage aerobic zone 02, the second-stage anoxic zone 03, and the second-stage anaerobic zone 04 all rely on the internal return facility to supplement the sludge concentration. The nitrified liquid sludge is lifted to the sludge pre-concentration zone 30 by the first sludge lifting pump 31 of the return channel 21. The sludge pre-concentration zone 30 is intended to concentrate the residual sludge in the biological pool. After the nitrified liquid sludge is concentrated by gravity in this area, the obtained supernatant enters the second-stage anoxic zone 03 or the second-stage anaerobic zone 04 through the connecting channel (flow hole), and the obtained concentrated sludge is then discharged from the biological pool by the second sludge lifting pump 32.

[0048] The calculation method of the sludge concentration and reflow ratio of the five-stage reaction zone of the two-stage AO circulation clarifier sewage treatment system is as follows: Under the premise that the reflow ratio is R and there is no raw water distribution in the second-stage anaerobic zone, the sludge concentration of the second-stage aerobic and sedimentation zone is controlled to be C0, then the sludge concentrations of the first-stage anoxic zone, the first-stage aerobic zone, the second-stage anoxic zone, and the second-stage anaerobic zone are R*C0 / (R+0.5), R*C0 / (R+0.5), R*C0 / (R+1), and R*C0 / (R+1) respectively. In theory, the sludge concentration of the second-stage aerobic and sedimentation zone is the highest, the sludge concentration of the first-stage anoxic zone and the first-stage aerobic zone is in the middle, and the sludge concentration of the second-stage anoxic zone and the second-stage anaerobic zone is the lowest.

[0049] By comparing the conventional A 2 / RPIR process and the two-stage AO circulation clarifier sewage treatment system of the utility model. If the sludge concentration in the aerobic and sedimentation zones is 5g / L, the conventional A 2 The sludge concentrations in the anaerobic zone, anoxic zone, aerobic zone and sedimentation zone of the / RPIR process were 3g / L, 4g / L and 5g / L respectively, while the sludge concentrations in the first-stage anoxic zone, first-stage aerobic zone, second-stage anoxic zone, second-stage anaerobic zone and second-stage aerobic and sedimentation zone of the two-stage AO / RPIR process were 4.44g / L, 4.44g / L, 4g / L, 4g / L and 5g / L respectively. It can be seen that compared with the conventional one-stage AA / RPIR process, this system has the following advantages: ① The carbon source in the raw water can be flexibly adjusted to different functional zones to ensure the most effective utilization of the carbon source; ② The nitrification liquid sludge in the first-stage aerobic zone all enters the second-stage anoxic zone, and the raw water and nitrification liquid sludge are in more complete contact, and the denitrification capacity is stronger; ③ It saves the energy consumption of an internal recirculation system; ④ The sludge concentration in the first-stage anoxic zone and the second-stage anaerobic zone is higher, which is more conducive to denitrification and phosphorus removal; ⑤ After releasing phosphorus in the second-stage anaerobic zone, the microorganisms enter the aerobic environment, and the phosphorus absorption power is used in time. The "starvation effect" can improve the effect of biological phosphorus removal.

[0050] In another embodiment, the sludge pre-concentration zone is connected to a return pump well, a first sludge lifting pump is provided in the return pump well, and the sludge pre-concentration zone is connected to the return pump well through the first sludge lifting pump.

[0051] In another embodiment, when the raw water is Q, part of the sewage (0.4Q) enters the first anoxic zone through the first water distribution hole, and another part of the sewage (0.4Q) enters the second anoxic zone through the second water distribution hole. At the same time, part of the sewage (0.2Q) is distributed to enter the second anaerobic zone through the third water distribution hole to meet the carbon source demand of anaerobic phosphorus release.

[0052] The above is only a specific implementation of the utility model, but the protection scope of the utility model is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the utility model, and these modifications or replacements should be included in the protection scope of the utility model. Therefore, the protection scope of the utility model should be based on the protection scope of the claims.

Claims

1. A two-stage AO circulation clarifier sewage treatment system, characterized in that: The invention comprises a biological pool and a nitrification liquid return facility, wherein the biological pool comprises a first-level anoxic zone, a first-level aerobic zone, a second-level anoxic zone, a second-level anaerobic zone and a second-level aerobic and sedimentation zone connected in sequence; the first-level anoxic zone and the second-level aerobic and sedimentation zone are connected through the nitrification liquid return facility.

2. The two-stage AO circulation clarifier sewage treatment system according to claim 1, characterized in that: It also includes a water distribution channel. The first-level anoxic zone is provided with a first water distribution hole, and the second-level anoxic zone is provided with a second water distribution hole. The first-level anoxic zone is connected to the water distribution channel through the first water distribution hole, and the second-level anoxic zone is connected to the water distribution channel through the second water distribution hole.

3. The two-stage AO circulation clarifier sewage treatment system according to claim 2, characterized in that: The second-stage anaerobic zone is provided with a third water distribution hole, and the second-stage anaerobic zone is connected to the water distribution channel through the third water distribution hole.

4. The two-stage AO circulation clarifier sewage treatment system according to claim 1, characterized in that: A circulating clarifier module is provided in the second-stage aerobic and sedimentation zone.

5. The two-stage AO circulation clarifier sewage treatment system according to claim 4, characterized in that: The nitrification liquid reflux facility comprises a reflux channel and a reflux pump well. The reflux channel is arranged between the second-stage aerobic and sedimentation zone and the first-stage anoxic zone, and the reflux pump well is arranged between the reflux channel and the second-stage aerobic and sedimentation zone.

6. The two-stage AO circulation clarifier sewage treatment system according to claim 5, characterized in that: The nitrification liquid reflux facility also includes a reflux pump, which is arranged between the reflux channel and the reflux pump well.

7. The two-stage AO circulation clarifier sewage treatment system according to claim 6, characterized in that: A decreasing aeration zone is arranged at one end of the first-stage aerobic zone close to the second-stage anoxic zone.

8. The two-stage AO circulation clarifier sewage treatment system according to claim 7, characterized in that: It also includes a sludge pre-concentration area, which is connected to a return pump well or a return channel.

9. The two-stage AO circulation clarifier sewage treatment system according to claim 8, characterized in that: A first sludge lifting pump is arranged in the reflux pump well or reflux channel, the sludge pre-concentration zone is connected with the reflux pump well or reflux channel through the first sludge lifting pump, and a second sludge lifting pump is arranged in the sludge pre-concentration zone.

10. The two-stage AO circulation clarifier sewage treatment system according to claim 8, characterized in that: The sludge pre-concentration zone is connected to the second-stage anoxic zone, the second-stage anaerobic zone or the second-stage aerobic and sedimentation zone through a connecting channel, and the connecting channel is a flow hole or a pipeline.

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