A circulating oxygen-controlled enhanced biochemical wastewater treatment system and process

Abstract

This invention provides a circulating oxygen-controlled enhanced biological wastewater treatment system and process. The circulating oxygen-controlled enhanced biological wastewater treatment system of this invention includes a tank, within which are sequentially connected a mixing zone, a screening zone, an enhanced biological treatment zone, a selection zone, a circulation zone, a sludge-water separation zone, and a return zone. The mixing zone has a wastewater inlet. The screening zone, enhanced biological treatment zone, and selection zone are respectively equipped with an aeration device and a dissolved oxygen meter to control the dissolved oxygen concentration. The circulation zone has an air-lift device. The sludge-water separation zone has a packing layer, a water outlet, and a sludge outlet. The sludge outlet is connected to the return zone, and the return zone is connected to the mixing zone so that at least a portion of the sludge is returned to the mixing zone. The system and process of this invention can remove different pollutants within the same tank and under the same microbial environment, offering advantages such as shortened treatment process, improved treatment efficiency, and reduced operating costs.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a circulating oxygen-controlled enhanced biochemical wastewater treatment system and process. Background Technology

[0002] Wastewater biological treatment is a secondary treatment method, primarily aimed at removing non-settleable suspended solids and dissolved biodegradable organic matter. It can be divided into biofilm processes and activated sludge processes. The activated sludge process is an aerobic biological wastewater treatment method. Under artificial aeration conditions, wastewater and various microbial communities are continuously mixed and cultured to form activated sludge. The activated sludge utilizes its bio-flocculation, adsorption, and oxidation processes to decompose and remove organic pollutants from the wastewater. The activated sludge process can remove dissolved and colloidal biodegradable organic matter, as well as suspended solids and other substances that can be adsorbed by the activated sludge, while also removing some phosphorus and nitrogen.

[0003] Currently, activated sludge processes mainly include the AB process, AO process, AAO process, and SBR process. The AB process is an adsorption-biodegradation process, where stage A is mainly for adsorption and stage B is mainly for biodegradation. The AO process is an anaerobic-aerobic process, where stage A is mainly for nitrogen and phosphorus removal and stage O is mainly for removing organic matter from the water. The AAO process is an anaerobic-anoxic-aerobic process, where the anaerobic stage is mainly for releasing phosphorus and ammonifying some organic matter, the anoxic stage is mainly for nitrogen removal, and the aerobic stage is mainly for BOD removal, nitrification, and phosphorus absorption. The SBR process is an activated sludge wastewater treatment technology that operates in an intermittent aeration mode. Its core is the SBR reactor, which integrates equalization, primary sedimentation, biodegradation, and secondary sedimentation functions, eliminating the need for a sludge return system.

[0004] However, the aforementioned traditional processes mostly require segmented removal of pollutants from wastewater in different tanks and at different stages. Furthermore, the microbial survival environment requirements for degrading COD, ammonia nitrogen, and total nitrogen are different, making it difficult to complete the process in the same tank and under the same microbial environment. This results in a waste of treatment tank space and time, and leads to a series of problems such as poor treatment effect, long treatment process, complex operation, and high operating cost.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a circulating oxygen-controlled enhanced biochemical wastewater treatment system and process, which can remove different pollutants in the same tank and under the same microbial environment.

[0007] This invention provides a circulating oxygen-controlled enhanced biochemical wastewater treatment system, comprising a tank body, in which a mixing zone, a screening zone, an enhanced biochemical zone, a selection zone, a circulation zone, a sludge-water separation zone, and a return zone are sequentially connected. A wastewater inlet is provided in the mixing zone. An aeration device and a dissolved oxygen meter are respectively provided in the screening zone, the enhanced biochemical zone, and the selection zone to control the dissolved oxygen concentration. An air-lifting device is provided in the circulation zone. A packing layer, a water outlet, and a sludge outlet are provided in the sludge-water separation zone. The sludge outlet is connected to the return zone, and the return zone is connected to the mixing zone so that at least a portion of the sludge is returned to the mixing zone.

[0008] Furthermore, the pool is a rectangular pool, which is divided into a first zone and a second zone in the width direction. The mixing zone, screening zone, enhanced biochemical zone and selection zone are arranged adjacent to each other in the first zone. The circulation zone, sedimentation zone and reflux zone are arranged adjacent to each other in the second zone. The circulation zone is adjacent to the selection zone and the reflux zone is adjacent to the mixing zone.

[0009] Furthermore, an overflow weir is provided between the mixing zone and the screening zone, and a structured composite packing is provided in the screening zone. In the screening zone, the specific microorganisms in the wastewater can adhere to the surface of the structured composite packing as they pass through it, and thus be intercepted in the screening zone.

[0010] Furthermore, the enhanced biochemical zone is equipped with an activated sludge inlet and a sludge concentration meter.

[0011] Furthermore, a sludge level gauge and a sludge discharge pump are installed in the selection area.

[0012] Furthermore, the sludge-water separation zone includes a packing sedimentation tank and a clear water zone. The packing sedimentation tank is provided with a water distribution zone, a packing layer and a sludge zone from top to bottom. The water distribution zone is connected to the clear water zone through the water outlet, and the sludge zone is connected to the return zone through the sludge outlet.

[0013] This invention also provides a circulating oxygen-controlled enhanced biological wastewater treatment process, which uses the above-mentioned circulating oxygen-controlled enhanced biological wastewater treatment system to treat wastewater, and the treatment includes the following steps:

[0014] S1: Wastewater is sent to the mixing zone and activated sludge is sent to the enhanced biochemical zone. Wastewater and sludge from the return zone are mixed in the mixing zone.

[0015] S2: The mixed wastewater enters the screening zone, enhanced biological treatment zone and selection zone in sequence for treatment. During the treatment process, the dissolved oxygen concentration in the screening zone, enhanced biological treatment zone and selection zone is controlled by aeration device and dissolved oxygen meter respectively.

[0016] S3: After treatment, the wastewater is circulated in the circulation zone and then enters the sludge-water separation zone for sludge-water separation. The clear water formed by sludge-water separation is discharged from the circulating oxygen-controlled enhanced biological wastewater treatment system, and the sludge formed by sludge-water separation enters the return zone. At least part of the sludge in the return zone is returned to the mixing zone.

[0017] Furthermore, controlling the dissolved oxygen concentration in the screening zone to 0.1-0.5 mg / L, for example, not only effectively screens denitrifying bacteria, but also retains and cultivates nitrifying, nitrite-oxidizing, and anaerobic ammonia-oxidizing bacteria, allowing the screening zone to undergo a denitrification reaction dominated by denitrifying bacteria, supplemented by nitrification and anaerobic ammonia oxidation. In contrast, traditional denitrification mainly occurs in anoxic zones, requiring dissolved oxygen levels below 0.2 mg / L, resulting in a relatively simple denitrification reaction and a lower denitrification rate.

[0018] Furthermore, the dissolved oxygen concentration in the enhanced biological treatment zone is controlled at 0.6-1.5 mg / L. Maintaining the dissolved oxygen concentration in this range promotes simultaneous nitrification and denitrification. Traditional aerobic aeration tanks typically control the dissolved oxygen concentration above 2 mg / L, and in actual operation, it is generally controlled at 4-5 mg / L. Compared to traditional aerobic aeration tanks, this invention maintains the dissolved oxygen concentration in the enhanced biological treatment zone at 0.6-1.5 mg / L, resulting in a relatively gentle aeration intensity. This creates a certain dissolved oxygen diffusion gradient inside and outside the activated sludge flocs, promoting multiple simultaneous nitrification and denitrification reactions, such as autotrophic denitrification and short-cut nitrification and denitrification. It also reduces the reliance on external carbon sources, lowers aeration volume, and saves electricity.

[0019] Furthermore, the dissolved oxygen concentration in the selection zone is controlled at 0.15-0.25 mg / L. Controlling the dissolved oxygen concentration in the selection zone within this range promotes the full release of phosphorus by phosphorus-removing bacteria. Compared with phosphorus release in traditional anaerobic zones, this invention effectively promotes the growth of phosphorus-releasing bacteria due to the lower dissolved oxygen concentration in the enhanced biochemical zone. The enrichment of denitrifying phosphorus-removing bacteria promotes the effective biological phosphorus removal process, accompanied by multiple processes such as autotrophic denitrification and simultaneous nitrification and denitrification reactions.

[0020] The circulating oxygen-controlled enhanced biological wastewater treatment system and process of this invention divides the main reaction zone into a screening zone, an enhanced biological zone, and a selective zone. By precisely controlling the dissolved oxygen in each zone, the screening zone is dominated by denitrifying bacteria to enhance nitrogen removal, while nitrification, nitrite oxidation, and anaerobic ammonia oxidation occur simultaneously to supplement nitrogen removal. The enhanced biological zone is accompanied by multiple biological reactions such as simultaneous nitrification and denitrification, autotrophic nitrogen removal, and short-cut nitrification and denitrification. These reactions proceed smoothly and efficiently simultaneously to remove various pollutants. The selective zone is dominated by denitrifying phosphorus-removing bacteria. The system incorporates multiple processes, including associated biological phosphorus removal, autotrophic denitrification, and simultaneous nitrification and denitrification. The three zones react together while simultaneously enhancing the advantages of each zone. Different reactions occur simultaneously in different zones without interference, resulting in more efficient removal. This allows for the removal of different pollutants within the same tank and under the same microbial environment. The system ensures that carbon removal and denitrification processes are integrated in both time and space, improving wastewater treatment capacity, reducing treatment time and energy consumption, and simplifying operation. It offers advantages such as shortened treatment processes, improved treatment efficiency, and reduced operating costs. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the structure of the circulating oxygen-controlled enhanced biochemical wastewater treatment system of the present invention.

[0023] Explanation of reference numerals in the attached figures:

[0024] 1: Mixing zone; 2: Screening zone; 3: Enhanced biochemical zone; 4: Selection zone; 5: Circulation zone; 6: Water distribution zone; 7: Packing layer; 8: Clear water zone; 9: Return zone. Detailed Implementation

[0025] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0026] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] Combination Figure 1 As shown, the circulating oxygen-controlled enhanced biochemical wastewater treatment system of this embodiment includes a tank body, in which a mixing zone 1, a screening zone 2, an enhanced biochemical zone 3, a selection zone 4, a circulation zone 5, a sludge-water separation zone, and a return zone 9 are sequentially connected. A wastewater inlet is provided in the mixing zone 1. An aeration device and a dissolved oxygen meter are respectively provided in the screening zone 2, the enhanced biochemical zone 3, and the selection zone 4 to control the dissolved oxygen concentration. An air lifting device is provided in the circulation zone 5. A packing layer 7, a water outlet, and a sludge outlet are provided in the sludge-water separation zone. The sludge outlet is connected to the return zone 9, and the return zone 9 is connected to the mixing zone 1 so that at least part of the sludge is returned to the mixing zone 1.

[0030] The tank is where wastewater undergoes various treatment processes. The arrangement of each zone within the tank is not strictly limited and can be rationally configured according to actual conditions. In this embodiment, the tank can adopt a rectangular or near-rectangular structure, which facilitates large-scale hydraulic circulation. The tank can be divided into a first zone and a second zone along its width. The mixing zone 1, screening zone 2, enhanced biochemical zone 3, and selection zone 4 can be sequentially arranged adjacent to each other in the first zone. The circulation zone 5, sedimentation zone, and reflux zone 9 can be sequentially arranged adjacent to each other in the second zone. The circulation zone 5 can be adjacent to the selection zone 4, and the reflux zone 9 can be adjacent to the mixing zone 1, thus saving reaction time. Furthermore, adjacent areas within the tank can share a wall, which facilitates large-scale circulation, saves space, and improves shock resistance.

[0031] Mixing zone 1 is mainly used for mixing raw water with sludge returned from self-returning zone 9. An overflow weir is set between mixing zone 1 and screening zone 2. The fully mixed wastewater enters screening zone 2 through the overflow weir. Structured composite packing is set in screening zone 2. When specific microorganisms in the wastewater pass through the structured composite packing, they can adhere to the surface of the structured composite packing and thus be intercepted in screening zone 2.

[0032] Aeration devices and a primary dissolved oxygen meter are installed in screening zone 2. The aeration devices aerate screening zone 2, and the primary dissolved oxygen meter monitors the dissolved oxygen concentration. The aeration devices can employ pulse-type oxygen supply, or wide-band / disc / tube / liftable flexible hose microporous aerators. Their high oxygenation capacity provides an appropriate amount of oxygen to the activated sludge in the zone. The dissolved oxygen concentration in screening zone 2 is controlled by adjusting the installation density of the aeration devices, maintaining a concentration of 0.1-0.5 mg / L. In screening zone 2, various microorganisms within the activated sludge undergo initial screening, with denitrifying bacteria becoming dominant, resulting in enhanced nitrogen removal. Simultaneously, nitrification, nitrite oxidation, and anaerobic ammonium oxidation reactions occur, providing supplementary nitrogen removal.

[0033] The enhanced biological treatment zone 3 is equipped with an activated sludge inlet and a sludge concentration meter. When the system starts operating, activated sludge is added to the enhanced biological treatment zone 3 through the activated sludge inlet, and the concentration of the activated sludge is monitored by the sludge concentration meter. The enhanced biological treatment zone 3 is the core area of ​​the entire system and process. It contains an aeration device and a second dissolved oxygen meter. The aeration device aerates the enhanced biological treatment zone 3, and the dissolved oxygen concentration is monitored by the second dissolved oxygen meter. The aeration device can be a wide-band microporous aerator. The dissolved oxygen concentration in the enhanced biological treatment zone 3 is controlled at 0.6-1.5 mg / L, which ensures the oxygen requirements for activated sludge oxidation of organic matter and also meets the environmental conditions for various biochemical reactions such as simultaneous nitrification and denitrification, autotrophic nitrogen removal, and short-cut nitrification and denitrification. All these reactions occur simultaneously and stably and efficiently within the enhanced biological treatment zone 3, thereby achieving the removal of various pollutants.

[0034] After passing through the enhanced biological treatment zone 3, the wastewater enters the selection zone 4. Selection zone 4 is equipped with an aeration device and a third dissolved oxygen meter. The aeration device aerates the selection zone, and the dissolved oxygen concentration is monitored and controlled at 0.15-0.25 mg / L. Various microorganisms within the activated sludge undergo further selection in selection zone 4. Phosphorus-removing bacteria dominate in selection zone 4. Selection zone 4 is equipped with a sludge level gauge and a sludge discharge pump. The sludge level gauge monitors the sludge level in selection zone 4, and the sludge discharge pump discharges sludge when the level is high. A portion of the selected activated sludge is discharged through the sludge discharge pump, while the majority of the sludge-water mixture enters the circulation zone 5. Multiple processes, including biological phosphorus removal, autotrophic denitrification, and simultaneous nitrification and denitrification, occur concurrently in selection zone 4.

[0035] An air-lift device is installed in circulation zone 5 to ensure the internal circulation of the mixed liquor and prevent sludge deposition within the entire zone. Wastewater passing through circulation zone 5 then enters the sludge-water separation zone, which includes a packed sedimentation tank and a clear water zone 8. The packed sedimentation tank, from top to bottom, consists of a water distribution zone 6, a packing layer 7, and a sludge zone (not shown). Water distribution zone 6 is connected to clear water zone 8 via an outlet, and the sludge zone is connected to return zone 9 via a sludge outlet. A portion of the sludge from return zone 9 is returned to mixing zone 1 to mix with the raw water, thus completing the overall system circulation.

[0036] The above-mentioned circulating oxygen-controlled enhanced biological wastewater treatment system can be used to treat wastewater, including the following steps: S1: Wastewater is sent to mixing zone 1, and activated sludge is sent to enhanced biological zone 3. Wastewater and sludge from return zone 9 are mixed in mixing zone 1; S2: The mixed wastewater sequentially enters screening zone 2, enhanced biological zone 3 and selection zone 4 for treatment. During the treatment process, the dissolved oxygen concentration in screening zone 2, enhanced biological zone 3 and selection zone 4 is controlled by aeration device and dissolved oxygen meter, respectively; S3: The treated wastewater is circulated in circulation zone 5 and then enters sludge-water separation zone for sludge-water separation. The clear water formed by sludge-water separation is discharged from the circulating oxygen-controlled enhanced biological wastewater treatment system, and the sludge formed by sludge-water separation enters return zone 9. At least a portion of the sludge in return zone 9 is returned to mixing zone 1.

[0037] During the treatment process, apart from controlling the dissolved oxygen concentration in screening zone 2 to 0.1-0.5 mg / L, the dissolved oxygen concentration in enhanced biochemical zone 3 to 0.6-1.5 mg / L, and the dissolved oxygen concentration in selection zone 4 to 0.15-0.25 mg / L, other process parameters are not strictly limited and can be adjusted according to the raw water quality.

[0038] In this embodiment, the circulating oxygen-controlled enhanced biological wastewater treatment system divides the main reaction zone into a screening zone 2, an enhanced biological zone 3, and a selection zone 4. By precisely controlling the dissolved oxygen in each zone, screening zone 2 is dominated by denitrifying bacteria to enhance nitrogen removal, while nitrification, nitrite oxidation, and anaerobic ammonium oxidation provide supplementary nitrogen removal. Enhanced biological zone 3 is accompanied by multiple biochemical reactions, including simultaneous nitrification and denitrification, autotrophic nitrogen removal, and short-cut nitrification and denitrification. These reactions proceed smoothly and efficiently simultaneously, achieving the removal of various pollutants. Selection zone 4 is dominated by denitrifying phosphorus-removing bacteria. The system incorporates multiple processes, including bio-phosphorus removal, autotrophic denitrification, and simultaneous nitrification and denitrification. While reacting together in three zones, each zone's advantages are amplified. Different reactions occur simultaneously in different zones without interference, resulting in more efficient removal. This allows for the removal of different pollutants within the same tank and microbial environment, ensuring that carbon removal and denitrification processes are integrated in both time and space. This improves wastewater treatment capacity, reduces treatment time and energy consumption, and simplifies operation, offering advantages such as shorter treatment processes, improved treatment efficiency, and reduced operating costs.

[0039] Example 2

[0040] The circulating oxygen-controlled enhanced biochemical wastewater treatment system described in Example 1 is used to treat urban wastewater; wherein, the water quality of the urban wastewater is: COD cr The dissolved oxygen concentrations were: 500 mg / L for COD, 300 mg / L for BOD5, 250 mg / L for SS, 30 mg / L for NH3-N, 40 mg / L for TN, and 5 mg / L for TP. The core process parameters were controlled as follows: dissolved oxygen concentration in screening zone 2 was 0.3 mg / L, dissolved oxygen concentration in enhanced biochemical zone 3 was 0.9 mg / L, and dissolved oxygen concentration in selection zone 4 was 0.2 mg / L. The treated water quality was: COD 500 mg / L, BOD5 300 mg / L, SS 250 mg / L, NH3-N 30 mg / L, TN 40 mg / L, and TP 5 mg / L. cr 50mg / L, BOD5 10mg / L, SS20mg / L, NH3-N 5mg / L, TN 15mg / L, TP 2mg / L.

[0041] Example 3

[0042] The circulating oxygen-controlled enhanced biochemical wastewater treatment system of Example 1 was used to treat heavily polluted wastewater; the wastewater quality of the heavily polluted wastewater was: COD cr The dissolved oxygen concentrations were: 8000 mg / L, BOD5 5000 mg / L, SS 2000 mg / L, NH3-N 1000 mg / L, TN 1200 mg / L. The core process parameters were controlled as follows: dissolved oxygen concentration in screening zone 2 was 0.1 mg / L, dissolved oxygen concentration in enhanced biochemical zone 3 was 1.0 mg / L, and dissolved oxygen concentration in selection zone 4 was 0.25 mg / L. The treated water quality was: COD 8000 mg / L, BOD5 5000 mg / L, SS 2000 mg / L, NH3-N 1000 mg / L, TN 1200 mg / L.cr 300mg / L, BOD5 20mg / L, SS 70mg / L, NH3-N 40mg / L, TN 70mg / L.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A circulating oxygen-controlled enhanced biochemical wastewater treatment system, characterized in that, The tank includes a rectangular tank body, within which are sequentially connected a mixing zone, a screening zone, an enhanced biological treatment zone, a selection zone, a circulation zone, a sludge-water separation zone, and a return zone. The mixing zone has a wastewater inlet. The screening, enhanced biological treatment, and selection zones are equipped with aeration devices and dissolved oxygen meters to control dissolved oxygen concentration. The circulation zone has an air-lift device. The sludge-water separation zone has a packing layer, a sludge outlet, and a sludge outlet. The sludge outlet connects to the return zone, and the return zone connects to the mixing zone to allow at least a portion of the sludge to return to the mixing zone. The tank body is rectangular, with the rectangular tank body extending in the width direction... The upper part is divided into a first zone and a second zone. The mixing zone, screening zone, enhanced biological treatment zone and selection zone are arranged adjacently in the first zone. The circulation zone, sedimentation zone and reflux zone are arranged adjacently in the second zone. The circulation zone is adjacent to the selection zone and the reflux zone is adjacent to the mixing zone. The sludge-water separation zone includes a packing sedimentation tank and a clear water zone. The packing sedimentation tank is arranged from top to bottom as a water distribution zone, a packing layer and a sludge zone. The water distribution zone is connected to the clear water zone through the outlet and the sludge zone is connected to the reflux zone through the sludge outlet. The dissolved oxygen concentration in the screening zone is controlled at 0.1-0.5 mg / L, the dissolved oxygen concentration in the enhanced biological treatment zone is controlled at 0.6-1.5 mg / L, and the dissolved oxygen concentration in the selection zone is controlled at 0.15-0.25 mg / L.

2. The circulating oxygen-controlled enhanced biochemical wastewater treatment system according to claim 1, characterized in that, An overflow weir is provided between the mixing zone and the screening zone, and a structured combination packing is provided in the screening zone.

3. The circulating oxygen-controlled enhanced biochemical wastewater treatment system according to claim 1, characterized in that, The enhanced biochemical zone is equipped with an activated sludge inlet and a sludge concentration meter.

4. The circulating oxygen-controlled enhanced biochemical wastewater treatment system according to claim 1, characterized in that, The selection area is equipped with sludge level gauges and sludge discharge pumps.

5. A circulating oxygen-controlled enhanced biochemical wastewater treatment process, characterized in that, Wastewater is treated using the circulating oxygen-controlled enhanced biochemical wastewater treatment system according to any one of claims 1-4, and the treatment includes the following steps: S1: Wastewater is sent to the mixing zone and activated sludge is sent to the enhanced biochemical zone. Wastewater and sludge from the return zone are mixed in the mixing zone. S2: The mixed wastewater enters the screening zone, enhanced biological treatment zone and selection zone in sequence for treatment. During the treatment process, the dissolved oxygen concentration in the screening zone, enhanced biological treatment zone and selection zone is controlled by aeration device and dissolved oxygen meter respectively. S3: After the treated wastewater is circulated in the circulation zone, it enters the sludge-water separation zone for sludge-water separation. The clear water formed by sludge-water separation is discharged from the circulating oxygen-controlled enhanced biological wastewater treatment system. The sludge formed by sludge-water separation enters the return zone, and part of the sludge in the return zone is returned to the mixing zone. The dissolved oxygen concentration in the screening zone was controlled at 0.1-0.5 mg / L, the dissolved oxygen concentration in the enhanced biochemical zone was controlled at 0.6-1.5 mg / L, and the dissolved oxygen concentration in the selection zone was controlled at 0.15-0.25 mg / L.

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