Continuous flow aerobic granular sludge culture method

Abstract

The invention discloses a continuous flow aerobic granular sludge culture method, and belongs to the technical field of sewage treatment. The method comprises the following steps: S1, sewage sequentially passes through an anaerobic zone, an anoxic zone and an aerobic zone for biochemical treatment; meanwhile, the aerobic zone is filled with a micro-ecological induction carrier, so that the attachment and aggregation of microorganisms and the initial granulation process are remarkably promoted; s2, controlling the surface load and the sedimentation time of the primary sedimentation tank, directionally screening and enriching granular sludge with excellent sedimentation performance, and returning the granular sludge to the aerobic zone; s3, carrying out secondary sedimentation on the mixed solution to obtain secondary sedimentation sludge; s4, heavy sludge obtained by separating the secondary settled sludge flows back to the anaerobic zone to serve as a particle flocculation core, a core framework is provided for formation of new particles, and particle growth is further accelerated. According to the method disclosed by the invention, the technical problems of slow starting and long period of granular sludge in a continuous flow process can be effectively solved through a triple synergistic mechanism of interface nucleation acceleration, skeleton reinforcement and dynamic screening enrichment.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and more specifically relates to a continuous flow aerobic granular sludge cultivation method. Background Art

[0002] Traditional biochemical processes for urban wastewater treatment primarily rely on the activated sludge process, a process known for its maturity and simplicity. "Sludge" refers to a muddy aggregate enriched with microorganisms, which absorb, decompose, and utilize pollutants in the wastewater for their growth and reproduction. While the activated sludge process is simple to operate and technologically mature, it utilizes flocculent sludge, which presents disadvantages such as low biochemical efficiency, long reaction times, slow sludge settling, prolonged sedimentation, and large system footprint.

[0003] Against this backdrop, aerobic granular sludge (AGS) technology, owing to its advantages such as excellent settling performance and tolerance to high organic loads, is considered an important development direction for the next generation of biological wastewater treatment. However, existing AGS technology still faces challenges in practical applications, such as slow granular sludge startup and a long formation cycle. Therefore, designing a continuous flow culture process suitable for rapid and stable aerobic granular sludge cultivation, while also being feasible in engineering, is of great practical significance.

[0004] A search revealed that patent CN109133337A discloses a continuous-flow aerobic granular sludge cultivation and preparation reactor, as well as a method for cultivating and acclimating aerobic granular sludge. This application, under continuous flow conditions, creates the "plug flow reaction" and "controllable selective pressure" conditions similar to those of an SBR reactor. This, coupled with the addition of calcium chloride solution ("nuclei") during the initial stages of granular sludge formation, rapidly and stably forms aerobic granular sludge, a biochemical reaction matrix dominated by aerobic particles, within the reaction system.

[0005] Patent CN112897685A discloses a continuous flow reactor device and operating method for rapidly forming aerobic granular sludge. In this application, a movable baffle directs the flow of gas released from the aeration disc, forcing the sludge-water mixture to form a longitudinally reciprocating "S"-shaped flow pattern within the aeration zone. This provides stronger and more regular hydraulic shear forces on the sludge, promoting the collision and aggregation of microorganisms and the secretion of large amounts of extracellular polymers, thus promoting the formation of aerobic granular sludge.

[0006] The above applications all involve technical improvements to the aerobic granular sludge formation process, but the industry still needs more diverse designs to solve practical problems such as slow startup and long cultivation cycle of continuous flow aerobic granular sludge. Summary of the Invention

[0007] 1. Problems to be solved

[0008] In view of at least some of the problems existing in the above prior art, the present invention proposes a continuous flow aerobic granular sludge cultivation method, which aims to solve the problems of slow granular sludge startup and long cycle in the existing continuous flow aerobic granular sludge cultivation.

[0009] 2. Technical solution

[0010] In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

[0011] A continuous flow aerobic granular sludge cultivation method of the present invention comprises the following steps:

[0012] S1. The sewage is biochemically treated in the anaerobic zone, anoxic zone and aerobic zone in sequence. Meanwhile, the aerobic zone is filled with microecological induction carriers to obtain a mixed liquid rich in flocculent sludge of a certain size.

[0013] S2, the mixed liquid enters the primary sedimentation tank through the outlet of the aerobic zone;

[0014] By controlling the surface load and sedimentation time of the primary sedimentation tank, the aerobic granular sludge in the mixed liquor is selectively settled to obtain primary granular sludge with good settling performance and controllable granular sludge particle size; and the primary granular sludge is returned to the aerobic zone to construct a forward reflux path of reaction-load and sedimentation screening-reflux-reaction; wherein,

[0015] At the initial start-up, the surface load of the primary sedimentation tank is controlled at 5-10m 3 / m 2 h, and the sedimentation time is greater than 45 minutes. At this stage, microbial aggregates are initially formed, with the embryonic form of granular sludge;

[0016] During the transition period, the surface load of the primary sedimentation tank is controlled at 10-20m 3 / m 2 h; and the settling time is greater than 30 minutes. At this stage, granular sludge is initially formed, but the particle size varies;

[0017] During the stable operation phase, the surface load of the primary sedimentation tank is increased to 20-40m 3 / m 2 ·h; and the settling time is less than 15 minutes. At this stage, the granular sludge structure is stable, and aerobic granular sludge within a certain particle size range can be selectively retained.

[0018] S3, after the first sedimentation, the mixed liquid enters the secondary sedimentation tank for secondary sedimentation to obtain secondary sedimentation sludge;

[0019] S4. The secondary sedimentation sludge is separated by a hydrocyclone, and the heavy sludge obtained after separation is returned to the anaerobic zone.

[0020] In some embodiments, at the initial start-up stage, the inlet flow rate of the hydrocyclone is 1.0-2.0 m / s and the split ratio is 50%-70%;

[0021] In the transition stage, the inlet flow rate of the hydrocyclone is 1.0-2.0 m / s and the split ratio is 30%-50%;

[0022] During the stable operation stage, the inlet flow velocity of the hydrocyclone is increased to 2.0-3.0 m / s, and the diversion ratio is maintained at 15-20%.

[0023] In some embodiments, the split ratio of the hydrocyclone at different stages is controlled by the installation angle of the hydrocyclone, specifically,

[0024] During the initial startup, the hydrocyclone is installed at an angle of -45° to -15°;

[0025] During the transition phase, the hydrocyclone is installed at an angle of -15° to 15°;

[0026] During the stable operation stage, the hydrocyclone is installed at an angle of 75 to 90 degrees.

[0027] In some embodiments, the judgment criteria for the startup phase are: at least two of the following must be met: SVI ≥ 80 mL / g, the proportion of particles with a particle size greater than 200 μm is less than 20%, and MLSS is less than 3000 mg / L with a fluctuation range greater than ±15%;

[0028] The judgment criteria for the transition stage are: at least two of the following must be met: 50mL / g≤SVI<80mL / g, the proportion of particles with a particle size greater than 200μm is 20%-60%, and MLSS is less than 3000mg / L and the fluctuation range is greater than ±15%;

[0029] The criteria for the stable operation stage are: at least two of the following must be met: SVI < 50 mL / g, the proportion of particles with a particle size > 200 μm ≥ 60% and continuous stability for ≥ 7 days, and MLSS between 4000-6000 mg / L and the fluctuation range < ±10%.

[0030] In some embodiments, part of the secondary settling sludge is directly returned to the anaerobic zone to replenish the microbial population in the anaerobic zone and maintain the stability of the sludge concentration.

[0031] In some embodiments, the light sludge separated by the hydrocyclone is directly discharged to the outside and / or enters the aerobic zone.

[0032] In some embodiments, the microecological induction carrier is selected from biological, organic or inorganic granular materials with a porous structure; the particle size of the microecological induction carrier is selected to be 0.05-0.2 mm, and the addition amount is 0.5%-1% of the effective volume of the aerobic zone.

[0033] In some embodiments, the microecological induction carrier is at least one of diatomaceous earth, biochar particles, activated carbon, expanded soil, and cellulose derivatives.

[0034] In some embodiments, the sludge load in the anaerobic zone is controlled at 0.6-0.8 kg COD / kg·MLSS·d, ensuring that most of the biodegradable organic matter in the influent is taken up in the anaerobic stage, thereby enhancing the growth of carbon source storage microorganisms such as phosphate accumulating bacteria and subsequent denitrifying bacteria;

[0035] The reflux ratio of nitrification liquid in the anoxic zone is controlled at 100%-200% to ensure denitrification reaction.

[0036] In some embodiments, the sludge load in the aerobic zone is reduced to 0.05-0.1 COD / kg·MLSS·d to prevent filamentous expansion and destabilization of the system.

[0037] 3. Beneficial effects

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The continuous flow aerobic granular sludge cultivation method of the present invention utilizes a microecological induction carrier as an adsorption center for microbial attachment, which can significantly promote the microbial attachment, aggregation and initial granulation process. At the same time, the introduction of return heavy sludge as the granular floc nucleus provides a core skeleton for the formation of new particles with its high density characteristics and excellent microbial community foundation, further accelerating the growth of particles. In addition, by regulating the flow rate and sedimentation time of the primary sedimentation tank to enhance the screening efficiency of particles and flocculent sludge, granular sludge with excellent sedimentation performance is selectively screened and enriched to achieve its rapid enrichment and structural stability, thereby forming a complete granular sludge cultivation and enhancement system, which can significantly shorten the cultivation cycle and improve the granulation efficiency and stability.

[0040] (2) In the continuous flow aerobic granular sludge cultivation method of the present invention, at the initial start-up stage, the hydrocyclone separates fine flocs with extremely poor settling properties with a mild screening force, while selectively retaining the weakly structured particles formed in the initial stage to avoid mistakenly selecting high-quality microbial populations with nucleation potential; as the particles gradually mature and their structural strength increases, the screening force of the hydrocyclone is gradually increased to selectively eliminate flocs with insufficient settling properties, further enrich mature particles with excellent settling properties, thereby continuously improving the overall quality of the particle group.

[0041] (3) In a continuous flow aerobic granular sludge cultivation method of the present invention, at the initial start-up stage, the hydrocyclone is installed at a negative angle, which prolongs the residence time of the coarse particles in the bottom flow and slows down their discharge rate, thereby providing more sufficient retention and development time for the initial particles with growth potential. In the transition stage, by appropriately increasing the installation angle, while protecting the coarse particles that have begun to take shape from excessive washing, small particles with insufficient sedimentation performance are effectively removed, thereby achieving a dynamic balance between separation efficiency and particle protection. In the stable operation stage, the hydrocyclone is adjusted to a larger positive angle installation, which accelerates the aggregation of large particles to the bottom flow by strengthening gravity sedimentation; at the same time, it avoids the discharge of mature coarse particles with overflow, thereby ensuring the efficient enrichment and stable maintenance of the particle population. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a process flow chart of a continuous flow aerobic granular sludge cultivation method of the present invention;

[0043] Figure 2 This is a schematic diagram of the hydrocyclone installed at a positive angle in the present invention;

[0044] Figure 3 This is a schematic diagram of the negative angle installation of the hydrocyclone in the present invention. DETAILED DESCRIPTION

[0045] In order to further understand the content of the present invention, the present invention is described in detail with reference to the accompanying drawings.

[0046] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0047] The present invention will be further described below with reference to specific embodiments.

[0048] Example 1

[0049] refer to Figure 1 As shown, the basic process of a continuous flow aerobic granular sludge cultivation method of this embodiment is as follows:

[0050] S1. After the sewage is anaerobically treated in the anaerobic zone, it is reacted with a nitrifying solution in the anoxic zone for anoxic treatment, and then aerobically treated in the aerobic reaction tank; at the same time, the aerobic zone is filled with a microecological induction carrier to obtain a mixed solution containing aerobic granular sludge;

[0051] S2. The mixed liquor enters the primary sedimentation tank through the outlet of the aerobic zone. By controlling the surface load and sedimentation time of the primary sedimentation tank, the aerobic granular sludge in the mixed liquor is selectively settled to obtain primary granular sludge with good settling performance. The primary granular sludge is then returned to the aerobic zone to establish a forward reflux path of reaction-loading and sedimentation screening-reflux-reaction.

[0052] S3, after the first sedimentation, the mixed liquid enters the sedimentation tank for secondary sedimentation to obtain secondary sedimentation sludge;

[0053] S4. The secondary sedimentation sludge is separated by a hydrocyclone, and the heavy sludge obtained after separation is returned to the anaerobic zone.

[0054] Specifically, in step S1, the sludge load in the anaerobic zone is controlled at 0.6-0.8 kgCOD / kg·MLSS·d to ensure that most of the biodegradable organic matter in the influent is taken up in the anaerobic stage, thereby enhancing the growth of carbon source storage microorganisms such as polyphosphate bacteria and subsequent denitrifying bacteria. A moderate sludge load is maintained in the anoxic zone, and the denitrification reaction is guaranteed by adjusting the nitrification liquid reflux ratio to 100%-200%. At the same time, the influent organic load is controlled and the MLSS concentration is increased in the aerobic zone to reduce the sludge load to 0.05-0.1 COD / kg·MLSS·d, so that it periodically enters a starvation metabolic state, thereby inhibiting the expansion of filamentous bacteria and promoting the formation of granular sludge. If the filamentous bacteria grow excessively (such as sludge swelling), their hyphae penetrate the interior of the particles, destroying the compact structure, causing the particles to break into flocculent sludge, which is obviously not conducive to the formation of aerobic granular sludge.

[0055] In traditional continuous flow systems, due to the lack of periodic selection pressure, granular microorganisms are difficult to spontaneously aggregate, and flocculent microorganisms often take advantage of their fast growth, resulting in a slow granulation process and easy failure. In the present embodiment, by filling the aerobic zone with a microecological induction carrier, the microecological induction carrier is used as an adsorption center for microbial attachment, and its special surface structure provides physical support and biological induction interface for microorganisms, which can significantly promote the attachment, aggregation and initial granulation process of microorganisms, thereby shortening the initial granulation startup time. At the same time, the physical anchoring effect of the microecological induction carrier on the microorganism can enhance the cross-linking density of the extracellular polymer (EPS) inside the particles, improve the structural stability of the initial particles, avoid the aggregate fragmentation caused by the impact of water flow, and help improve the stability of the particle structure.

[0056] Preferably, the microecological inducing carrier is added directly to the aerobic zone during the initial system startup and mixed evenly with the incoming water. The particle size is selected to be 0.05-0.2 mm, for example, 0.08 mm, 0.12 mm, 0.18 mm, etc. The dosage is 0.5%-1% of the effective volume of the reactor, for example, 0.6%, 0.8%, etc.

[0057] In some embodiments, the microecological induction carrier is selected from biological, organic or inorganic granular materials with a porous structure, including but not limited to one or a combination of diatomaceous earth, biochar particles, activated carbon, expanded soil, and cellulose derivatives.

[0058] For the convenience of the following description, the entire cultivation process is divided into the initial start-up phase, the transition phase, and the stable operation phase. The judgment criteria for each phase are:

[0059] The judgment criteria for the startup phase include: (1) SVI ≥ 80 mL / g; (2) the proportion of particles with a particle size greater than 200 μm is less than 20%; (3) MLSS is less than 3000 mg / L and the fluctuation range is greater than ±15%; among them, SVI is the sludge volume index; MLSS is the suspended solids concentration of the mixed liquor.

[0060] The criteria for the transition phase include: (1) 50 mL / g ≤ SVI < 80 mL / g; (2) the proportion of particles with a particle size > 200 μm is 20%-60%; (3) MLSS < 3000 mg / L and the fluctuation range is > ±15%;

[0061] The criteria for judging the stable operation stage include: (1) SVI < 50 mL / g; (2) the proportion of particles with a particle size > 200 μm is ≥ 60% and is continuously stable for ≥ 7 days; (3) MLSS is between 4000-6000 mg / L and the fluctuation range is < ± 10%.

[0062] It is worth mentioning that each stage does not need to meet all the conditions of the corresponding judgment criteria, but only needs to meet two or more of the corresponding judgment criteria.

[0063] In this embodiment, a primary sedimentation tank is set at the outlet of the aerobic zone, and the primary granular sludge in the primary sedimentation tank is returned to the aerobic zone to form a "structure-driven" spatial selection mechanism. The core is to utilize the difference in sedimentation performance between particles and flocs to achieve graded enrichment of sludge structure, thereby achieving accurate screening and positive retention of granular sludge. However, the particle formation state in different operating stages is significantly different. If the primary sedimentation tank adopts a uniform surface load and sedimentation time, it will be difficult to match the particle growth requirements, resulting in an imbalance between screening efficiency and particle stability. Therefore, it is necessary to design a dynamically adjustable surface load for different operating stages to achieve precise regulation. Specifically,

[0064] At the initial stage of startup, microbial aggregates have been initially formed in the system, but the particles are not yet mature and only have the embryonic form of granular sludge. At this stage, the surface load of the primary sedimentation tank needs to be controlled at 5-10m 3 / m 2 h; at the same time, extend the sedimentation time to more than 45 minutes to prolong the contact time between mud and water, ensure the sedimentation opportunity of micro-clusters and primary particles, and avoid high-quality particles being discharged before they are formed.

[0065] In the transition stage, the particle structure begins to form gradually, and the granular sludge has been initially formed, but the particle size varies, and the structure is unstable and fluctuates greatly. In this stage, the surface load needs to be maintained at 10-20m 3 / m 2 h, without making drastic adjustments to avoid external interference that disrupts the particle self-organization process. At the same time, the sedimentation time is greater than 30 minutes.

[0066] In the stable operation stage, the particles are mature, the structure is good, and the sedimentation is increased; at this time, the surface load can be gradually increased to 20-40m 3 / m 2 h, and the settling time is less than 15 minutes; this strengthens the elimination mechanism and accelerates the removal of residual flocs and unstable particles with loose structure and poor settling performance, ensuring efficient return of large particles and improving the stable circulation rate of the system.

[0067] In this embodiment, the heavy sludge separated by the hydrocyclone is returned to the anaerobic zone to serve as flocculants and to replenish the microbial population and maintain sludge concentration in the anaerobic zone. If the heavy sludge separated by the hydrocyclone does not meet the sludge return flow rate, the unseparated sludge at the bottom of the secondary sedimentation tank can be directly returned to the anaerobic zone.

[0068] In some embodiments, a portion of the light sludge separated by the hydrocyclone is returned to the aerobic zone to establish a directional particle return path, providing microbial carriers and growth substrates for particle regrowth, promoting further aggregation and strengthening structure in the aerobic environment, and forming a complete granulation circulation system.

[0069] In this embodiment, the specific operating parameters of the hydrocyclone at different stages are as follows:

[0070] During the initial startup phase, particles are small and easily broken. The inlet flow rate is maintained at 1.0-2.0 m / s. The split ratio is controlled to 50%-70% by adjusting the hydrocyclone's installation angle. This reduces shear shock and particle breakage while allowing immature particles to flow back to the aerobic zone for continued cultivation.

[0071] During the transition phase, when particle formation is accelerated and the structure fluctuates, the inlet flow rate is controlled at 1.0-2.0 m / s and the split ratio is controlled at 30%-50% to avoid excessive disturbance to the system.

[0072] During the stable operation stage, as the particles gradually mature and their structure strengthens, the cyclone inlet flow rate increases to 2.0-3.0 m / s, and the diversion ratio is maintained at 15%-20%. The screening efforts are strengthened, and flocs with insufficient settling performance are eliminated in a targeted manner to improve the overall quality of the particle group.

[0073] In this embodiment, the hydrocyclone separation efficiency is low during the initial startup and transition phases of the system. By adjusting the installation angle, the diversion ratio and separation efficiency can be increased over a wide range, reducing sludge loss during aerobic granular sludge screening and enrichment. The hydrocyclone's installation angle not only affects the separation strength and flow field stability within the cyclone, but also directly determines the relative elevation of the underflow and overflow outlets, thereby affecting the destination and return flow path of particles of different particle sizes. Therefore, in this embodiment, the hydrocyclone's installation angle is set in stages according to different operating stages to optimize the directional screening effect.

[0074] refer to Figure 2 、 Figure 3 As shown, in this embodiment, the hydrocyclone can be installed at either a positive or negative angle. In a positive angle, the underflow port is lower than the overflow port, while in a negative angle, the underflow port is higher than the overflow port. It is worth noting that the hydrocyclone in this embodiment is conventionally installed vertically, with the overflow port located at the top, diverting light sludge, and the underflow port located at the bottom, diverting heavy sludge.

[0075] In this embodiment, an inclined installation method is adopted. Specifically, in the initial startup phase, the hydrocyclone is installed at a relatively large negative angle, preferably -45° to -15°, for example, -40°, -30°, -20°, etc., to account for the immature particles, small particle size distribution, and low solid content in the underflow. This extends the residence time of the coarse underflow particles, slows their discharge rate, and provides more time for the early particles with growth potential to remain and grow.

[0076] During the transition phase, as particles gradually grow larger but structural stability is still developing, the hydrocyclone is installed at an angle of -15° to 15°, such as -10°, -5°, and 10°. This design protects coarse particles from excessive washing while effectively removing small particles with insufficient settling performance, achieving a dynamic balance between separation efficiency and particle protection.

[0077] During the stable operation phase, when the particle structure is more mature and the proportion of large particles increases significantly, the hydrocyclone is adjusted to a larger positive angle, preferably 75-90 degrees, for example, 78 degrees, 86 degrees, etc. This design accelerates the accumulation of large particles in the underflow by enhancing gravity settling, while preventing mature coarse particles from being discharged with overflow, ensuring efficient enrichment and stable maintenance of the particle population.

[0078] Example 2

[0079] A continuous flow aerobic granular sludge cultivation method of this embodiment can observe the state of particles in the aerobic zone through an image recognition system, and judge the particle quality by optical particle size analysis and statistics of the proportion of particles in each particle size range, thereby providing a standard for judging different operation stages, and based on different judgment results, the operating parameters of the primary sedimentation tank and hydrocyclone are adjusted in real time.

[0080] Specifically, the graphic recognition system is installed at a water depth of 1 / 2 to 2 / 3 below the liquid surface of the aerobic pool. The configuration includes: ① High-definition camera module with automatic focus and high-speed shutter functions to adapt to the movement state of particles; ② Directional light source system: using backlighting to improve the clarity of particle edges and image contrast; ③ Image processing module: deployed on the edge computing unit or main control platform to perform real-time data processing.

[0081] Operational Process: The system automatically captures multiple frames of particle images every 5-10 minutes and calculates the equivalent spherical particle size using edge extraction, morphological segmentation, and area measurement algorithms. It also checks particle edge integrity and internal grayscale uniformity, identifying agglomerated particles, broken particles, and flocculent particles. The processing module outputs key indicators such as the percentage of particles by size, volume distribution, and structural anomalies.

[0082] The above is a schematic description of the present invention and its embodiments, which is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs a structure and embodiment similar to this technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. A continuous flow aerobic granular sludge cultivation method comprising the following steps: S1. The sewage is biochemically treated in the anaerobic zone, anoxic zone and aerobic zone in sequence. Meanwhile, the aerobic zone is filled with microecological induction carriers to obtain a mixed liquid rich in flocculent sludge of a certain size. S2, the mixed liquid enters the primary sedimentation tank through the outlet of the aerobic zone; By controlling the surface load and sedimentation time of the primary sedimentation tank, the aerobic granular sludge in the mixed liquor is selectively settled to obtain primary granular sludge with good settling performance and controllable granular sludge particle size; The primary granular sludge is returned to the aerobic zone to construct a forward reflux path of reaction-load and sedimentation screening-reflux-reaction; wherein, At the initial start-up, the surface load of the primary sedimentation tank is controlled at 5-10m 3 / m 2 h, and the sedimentation time is greater than 45 minutes. At this stage, microbial aggregates are initially formed, with the embryonic form of granular sludge; During the transition period, the surface load of the primary sedimentation tank is controlled at 10-20m 3 / m 2 h; and the settling time is greater than 30 minutes. At this stage, granular sludge is initially formed, but the particle size varies; During the stable operation phase, the surface load of the primary sedimentation tank is increased to 20-40m 3 / m 2 ·h; and the settling time is less than 15 minutes. At this stage, the granular sludge structure is stable, and aerobic granular sludge within a certain particle size range can be selectively retained. S3, after the first sedimentation, the mixed liquid enters the secondary sedimentation tank for secondary sedimentation to obtain secondary sedimentation sludge; S4. The secondary sedimentation sludge is separated by a hydrocyclone, and the heavy sludge obtained after separation is returned to the anaerobic zone.

2. The continuous flow aerobic granular sludge cultivation method according to claim 1, characterized in that: At the initial start-up, the inlet flow rate of the hydrocyclone is 1.0-2.0 m / s and the split ratio is 50%-70%; In the transition stage, the inlet flow rate of the hydrocyclone is 1.0-2.0 m / s and the split ratio is 30%-50%; During the stable operation stage, the inlet flow velocity of the hydrocyclone is increased to 2.0-3.0 m / s, and the diversion ratio is maintained at 15-20%.

3. The continuous flow aerobic granular sludge cultivation method according to claim 2, characterized in that: The split ratio of the hydrocyclone at different stages is controlled by the installation angle of the hydrocyclone, specifically, During the initial startup, the hydrocyclone is installed at an angle of -45° to -15°; During the transition phase, the hydrocyclone is installed at an angle of -15° to 15°; During the stable operation stage, the hydrocyclone is installed at an angle of 75 to 90 degrees.

4. A continuous flow aerobic granular sludge cultivation method according to any one of claims 1 to 3, characterized in that: The judgment criteria for the startup phase are: at least two of the following must be met: SVI ≥ 80 mL / g, particle size > 200 μm particle proportion < 20%, MLSS < 3000 mg / L with a fluctuation range > ± 15%; The judgment criteria for the transition stage are: at least two of the following must be met: 50mL / g≤SVI<80mL / g, the proportion of particles with a particle size greater than 200μm is 20%-60%, and MLSS is less than 3000mg / L and the fluctuation range is greater than ±15%; The criteria for the stable operation stage are: at least two of the following must be met: SVI < 50 mL / g, the proportion of particles with a particle size > 200 μm ≥ 60% and continuous stability for ≥ 7 days, and MLSS between 4000-6000 mg / L and the fluctuation range < ±10%.

5. The continuous flow aerobic granular sludge cultivation method according to claim 1, characterized in that: In step S4, part of the secondary sedimentation sludge is directly returned to the anaerobic zone to replenish the microbial population in the anaerobic zone and maintain the stability of the sludge concentration.

6. The continuous flow aerobic granular sludge cultivation method according to claim 5, characterized in that: In step S3, the light sludge separated by the hydrocyclone is directly discharged to the outside and / or enters the aerobic zone.

7. The continuous flow aerobic granular sludge cultivation method according to claim 1, characterized in that: The microecological induction carrier is selected from biological, organic or inorganic granular materials with a porous structure; the particle size of the microecological induction carrier is selected to be 0.05-0.2 mm, and the addition amount is 0.5%-1% of the effective volume of the aerobic zone.

8. The continuous flow aerobic granular sludge cultivation method according to claim 7, characterized in that: The microecological induction carrier is at least one of diatomaceous earth, biochar particles, activated carbon, expanded soil, and cellulose derivatives.

9. The continuous flow aerobic granular sludge cultivation method according to claim 1, characterized in that: In step S1, the sludge load in the anaerobic zone is controlled at 0.6-0.8 kg COD / kg·MLSS·d, ensuring that most of the biodegradable organic matter in the influent is absorbed during the anaerobic stage, thereby enhancing the growth of carbon source microorganisms in the storage and subsequent denitrifying bacteria; The reflux ratio of nitrification liquid in the anoxic zone is controlled at 100%-200% to ensure denitrification reaction.

10. The continuous flow aerobic granular sludge cultivation method according to claim 9, characterized in that: In step S1, the sludge load in the aerobic zone is reduced to 0.05-0.1COD / kg·MLSS·d to prevent filamentous expansion and damage to the system stability.

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