Aerobic granular sludge rapid culture and stable control method based on anaerobic-aerobic alternate operation

Abstract

The invention discloses an aerobic granular sludge rapid culture and stable control method based on anaerobic-aerobic alternate operation, and belongs to the technical field of biological sewage treatment.The method comprises a rapid nucleation induction stage, a granulation promotion stage and a stable operation regulation stage, functional microorganisms are enriched through anaerobic-aerobic alternate operation, nucleation is accelerated through stepped sedimentation time, stability is maintained through two-parameter linkage regulation and control, granulation can be completed within 21-28 days, and the total nitrogen removal rate reaches 70% or above.

Description

Technical Field

[0001] This invention belongs to the field of wastewater biological treatment technology, specifically relating to a method for rapid cultivation and stable control of aerobic granular sludge based on alternating anaerobic and aerobic operation. Background Technology

[0002] Aerobic granular sludge is a dense, spherical bioaggregate formed by microorganisms under aerobic conditions. Compared with traditional flocculent activated sludge, it has significant advantages such as faster settling speed, higher biomass concentration, stronger resistance to shock loads, and simultaneous nitrogen and phosphorus removal. A research team at Delft University of Technology in the Netherlands developed the Nereda process based on the "abundance-starvation" theory. Nearly 100 aerobic granular sludge wastewater treatment plants operating in sequencing batch reactors have been built worldwide, demonstrating outstanding engineering value by saving more than 70% of land area and reducing energy consumption by more than 30%.

[0003] However, existing aerobic granular sludge cultivation technologies still face two major bottlenecks. The first bottleneck is the excessively long cultivation cycle. Conventional methods use hydraulic selective pressure to screen for microbial aggregates with good settling performance by gradually shortening the settling time. This process typically takes 40-90 days to complete granulation, and some cultivation experiments using low-concentration actual wastewater as influent even require more than 100 days. This excessively long cultivation cycle means that newly built or renovated wastewater treatment facilities need to undergo a lengthy start-up and commissioning phase before operation, which severely restricts the efficiency and economic feasibility of engineering promotion of aerobic granular sludge technology. Chinese patent CN101428907B discloses a method for cultivating granular sludge in an anaerobic / anoxic-aerobic sequencing batch reactor, which promotes the enrichment and growth of functional microorganisms by setting anaerobic and anoxic sections. However, this method does not involve a step-by-step dynamic control strategy for settling time, and the reduction of settling time lacks a systematic, phased plan, resulting in a still relatively long granulation cycle. Chinese patent CN108191049A discloses a method for cultivating aerobic granular sludge, which accelerates the granulation process by adding anaerobic granular sludge as crystal nuclei. While this can shorten the cultivation time to some extent, relying on exogenous anaerobic granular sludge as crystal nuclei increases operating costs. Furthermore, the source and quality of the anaerobic granular sludge are limited by the operational status of upstream anaerobic treatment facilities, making it difficult to promote its application in areas lacking such facilities. International PCT patent WO2022213619A1 discloses a method for enhancing the cultivation of aerobic granular sludge, involving promoting granulation through hydraulic condition optimization, but lacks specific measures for targeted regulation of the microbial community.

[0004] The second bottleneck is insufficient operational stability. Aerobic granular sludge is prone to problems such as particle breakup, excessive growth of filamentous bacteria, and sludge bulking during long-term operation, leading to deterioration of effluent quality. Current technologies lack effective online monitoring and active control methods, mostly relying on post-event remedial measures. Although some researchers have proposed maintaining particle stability by adjusting aeration intensity or organic load in recent years, these methods lack a systematic multi-parameter linkage control mechanism, making it difficult to achieve feedforward control for stability.

[0005] Furthermore, existing aerobic granular sludge cultivation methods also have significant shortcomings in terms of nitrogen removal performance. Due to the lack of effective strategies for constructing alternating anaerobic and aerobic environments, the functional microbial stratification structure inside the granules is not perfect, resulting in low simultaneous nitrification and denitrification efficiency. The total nitrogen removal rate is typically only 40% to 60%, which is insufficient to meet increasingly stringent wastewater discharge standards.

[0006] Therefore, there is an urgent need to develop a rapid cultivation and stable control method for aerobic granular sludge that can shorten the cultivation cycle, improve operational stability, and enhance nitrogen and phosphorus removal performance. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for the rapid cultivation and stable control of aerobic granular sludge based on alternating anaerobic and aerobic operation. This method enriches slowly growing functional microorganisms, particularly polyphosphate-accumulating bacteria and polysaccharide-accumulating bacteria, as the core framework of the granules through an alternating anaerobic and aerobic operation mode; accelerates granule nucleation through a stepwise selective pressure strategy that gradually increases hydraulic screening from mild to strong; and achieves proactive early warning and rapid recovery of operational stability through a dual-parameter monitoring system combined with multi-dimensional synergistic regulation. The synergistic effect of these three mechanisms allows for granulation cultivation to be completed within 21–28 days, with the 30-minute sludge volume index of the granular sludge remaining stable at 35–55 mL / g, a chemical oxygen demand (COD) removal rate exceeding 95%, and a total nitrogen removal rate exceeding 70%. The sludge can operate stably continuously for over 180 days.

[0008] The technical solution of this invention comprises three sequential stages: a rapid nucleation induction stage, a granulation promotion stage, and a stable operation control stage. In the rapid nucleation induction stage, an anaerobic stirred influent mode and a stepped settling time strategy implemented in three progressive gradients are used to gradually increase the hydraulic selective pressure while maintaining sufficient microbial substrate, promoting the rapid formation of initial aggregates centered on slowly growing microorganisms. In the granulation promotion stage, an alternating anaerobic-aerobic environment is set up in each operating cycle, and an easily degradable carbon source is added in the anaerobic section to form a substrate pulse, promoting the directed secretion of protein components in extracellular polymers and the stratified enrichment of functional microorganisms in the radial direction of the particles. The protein-to-polysaccharide mass ratio is used as a quantitative indicator of granulation completion. In the stable operation control stage, early warning of operational instability is achieved through online monitoring of both sludge volume index and granulation rate. Combined with multi-dimensional synergistic control measures such as organic load adjustment, carbon-to-nitrogen ratio control, phosphorus release maintenance, and selective sludge discharge, the system's stable state is rapidly restored.

[0009] Compared with existing technologies, the beneficial effects of this invention are as follows: the cultivation cycle is shortened from 40-90 days in traditional methods to 21-28 days, a reduction of more than 50%; the granulation process does not require the addition of exogenous crystal nuclei, and relies entirely on in-situ endogenous induction to achieve particle nucleation, thus reducing operating costs; through a dual-parameter monitoring system, proactive early warning and multi-dimensional synergistic regulation of stability are achieved, and granular sludge can operate continuously and stably for more than 180 days without system collapse; the total nitrogen removal rate reaches more than 70%, which is 10-30 percentage points higher than conventional methods. This is due to the formation of a complete functional microbial stratification structure inside the particles by polyphosphate-accumulating bacteria enriched in the anaerobic-aerobic alternating mode. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the stepped settlement time strategy of the present invention.

[0011] Figure 2 This is a schematic diagram of the time allocation for each stage of a single operating cycle of the present invention.

[0012] Figure 3 This is a graph showing the changes in sludge volume index and granulation rate over 30 minutes during the granulation cultivation process in Example 1 of the present invention.

[0013] Figure 4 This is a graph showing the change in the ratio of extracellular polymeric protein to polysaccharide during the granulation culture process in Example 1 of the present invention over time.

[0014] Figure 5 This is a comparison chart of the particle formation completion time and total nitrogen removal rate of various embodiments and comparative examples of the present invention.

[0015] Figure 6This is a monitoring curve of sludge volume index and granulation rate for 30 minutes within 180 days during the stable operation phase of Embodiment 1 of the present invention. Detailed Implementation

[0016] The technical solution of the present invention will be described in detail below with reference to specific embodiments. Those skilled in the art should understand that the following embodiments are only used to illustrate the technical solution of the present invention and are not intended to limit the scope of protection of the present invention.

[0017] The present invention describes a method for rapid cultivation and stable control of aerobic granular sludge based on alternating anaerobic and aerobic operation. Its core lies in the systematic coupling of three mechanisms: anaerobic selective enrichment of functional microorganisms, step-type hydraulic selective pressure to accelerate nucleation, and dual-parameter linkage feedback regulation, to achieve rapid formation and long-term stable operation of aerobic granular sludge in a sequencing batch reactor.

[0018] Regarding the basic configuration of the reactor, this invention uses a cylindrical sequencing batch reactor as the cultivation device. The reactor is made of plexiglass or stainless steel, preferably plexiglass to facilitate direct observation of the granulation process. The height-to-diameter ratio of the reactor should be controlled within the range of 4:1 to 8:1, preferably 6:1. A larger height-to-diameter ratio is beneficial for forming a sufficient internal circulation flow during aeration, providing a uniform hydraulic shear environment for the sludge particles. A microporous aeration disc is installed at the bottom of the reactor for aeration and oxygen supply. The micropore diameter of the aeration disc is 50-80 μm, which can generate a uniform and dense bubble distribution, ensuring sufficient oxygen mass transfer efficiency and forming a moderate hydraulic shear force. A drain outlet controlled by a solenoid valve is installed in the middle of the reactor for periodic drainage. The drain outlet is located at 50% of the effective height of the reactor, and the drainage ratio is controlled at 40%-60%, preferably 50%. The top of the reactor is open for sampling and observation. A splash guard can be installed as needed during the cultivation process. The reactor is equipped with a mechanical agitator featuring a double-layered inclined blade design. The agitation speed is controlled within the range of 60–100 r / min, ensuring thorough mixing of the anaerobic solution without introducing air to avoid disrupting the anaerobic environment during the anaerobic phase. The influent system uses a peristaltic pump to inject water from the bottom of the reactor. The influent pipe diameter is 6–10 mm, and the influent flow rate is adjustable from 10–200 mL / min. The reactor is also equipped with online dissolved oxygen monitoring probes, online pH monitoring probes, and a temperature sensor. All online monitoring data is recorded in real-time through a data acquisition system, and warning thresholds can be set. Temperature control employs a constant-temperature water bath circulation system, achieving precise temperature control through a circulating water jacket surrounding the reactor wall. The reactor's operating temperature is maintained within the range of 20–30℃ throughout the cultivation process, preferably 25℃. The influent pH value is adjusted to the range of 6.8–7.5 by adding dilute hydrochloric acid or sodium hydroxide solution. The total operating time for each cycle is 4–6 hours, preferably 4 hours, with 6 cycles per day. Regarding the influent water quality, artificial simulated wastewater or pretreated actual urban domestic sewage can be used as the influent water source. The influent chemical oxygen demand concentration is 200~600 mg / L, ammonia nitrogen concentration is 20~60 mg / L, and total phosphorus concentration is 4~12 mg / L.

[0019] Regarding the specific operation of Step 1, the rapid nucleation induction stage, the goal of this stage is to form the initial nuclei of granular sludge in the shortest possible time. First, activated sludge is inoculated into the sequencing batch reactor. The inoculated sludge is taken from the secondary sedimentation tank return sludge of a municipal wastewater treatment plant, with an initial sludge volume index of 120–200 mL / g and an initial sludge concentration controlled at 3000–4000 mg / L MLSS. After inoculation, a stepped settling time strategy is implemented, such as… Figure 1As shown, this strategy divides the initial cultivation phase into three progressive selection pressure gradients. The first gradient occurs from days 1 to 7, with a settling time controlled at 15–20 min. The purpose of this stage is to allow the inoculated sludge to gradually adapt to the reactor environment and begin initial microbial aggregation. The longer settling time avoids drastic biomass loss due to excessive elimination. The second gradient occurs from days 8 to 14, with a settling time shortened to 8–12 min. During this stage, loose flocs with poor settling performance are largely eliminated, while dense microbial aggregates gain a competitive advantage and accelerate growth. The third gradient occurs from day 15 until the end of the cultivation phase, with a stable settling time of 3–5 min. Only dense particles with a settling velocity greater than 5 m / h are retained in the reactor.

[0020] The use of anaerobic stirred influent is another key operation in this stage. Influent is slowly injected from the bottom of the reactor via a peristaltic pump for 20–40 minutes, preferably 30 minutes. Mechanical stirring is activated during influent, but aeration is not performed. Stirring ensures thorough mixing of the influent with the sludge in the reactor, while maintaining an anaerobic environment and keeping the dissolved oxygen concentration below 0.2 mg / L. To ensure rapid establishment of the anaerobic environment, nitrogen can be briefly introduced before influent begins, or residual dissolved oxygen can be consumed by the aerobic metabolism of microorganisms in the previous cycle's residual mixed liquor. This anaerobic influent mode creates a favorable selection environment for polyphosphate-accumulating bacteria (PABs) and polysaccharide-accumulating bacteria. Under anaerobic conditions, PPAs can utilize readily degradable organic carbon sources in the influent, especially volatile fatty acids, to synthesize intracellular carbon storage substances such as poly(β-hydroxybutyrate). Simultaneously, they hydrolyze intracellular polyphosphates to release orthophosphates to obtain the energy needed for synthesizing intracellular carbon storage substances; this process is microbiologically termed anaerobic phosphorus release. The metabolic pathways of polysaccharitrophs under anaerobic conditions differ fundamentally from those of polyphosphate-accumulating bacteria. Polysaccharitrophs obtain metabolic energy by hydrolyzing intracellular glycogen accumulated during the aerobic phase. They then utilize this energy to absorb volatile fatty acids from the influent and convert them into polyhydroxyalkanoates (PHA) for intracellular storage. Therefore, the anaerobic metabolism of polysaccharitrophs exhibits a biphasic coupling process of glycogen consumption and PHA accumulation. In the subsequent aerobic phase, polysaccharitrophs resynthesize glycogen by oxidizing PHA, completing the metabolic cycle. These two types of slow-growing functional microorganisms have a competitive advantage in utilizing volatile fatty acids under anaerobic conditions, while aerobic heterotrophic bacteria, lacking similar carbon storage capabilities, are gradually eliminated in anaerobic-aerobic alternating environments. Since both polyphosphate-accumulating bacteria and polysaccharitrophs are slow-growing microbial groups, their maximum specific growth rate is typically only one-third to one-half that of aerobic heterotrophic bacteria. The microbial aggregates they form have a more compact and stable structure due to their slow growth rate, with a density higher than typical activated sludge flocs, making them ideal cores for the formation of aerobic granular sludge. At the end of the rapid nucleation induction stage, around day 14-15 of operation, visible microbial aggregates with a particle size of about 0.2-0.5 mm can be observed in the reactor. The color gradually changes from the initial brownish-yellow to yellowish-brown, and the settling speed is significantly accelerated, indicating that the initial nucleus has been formed and the conditions for entering the next stage of granulation promotion are met.

[0021] Regarding the specific operation of step two, the granulation promotion stage, the purpose of this stage is to promote the rapid development of the already formed initial core into mature aerobic granular sludge. A clearly defined anaerobic-aerobic alternating environment is established within each operating cycle to form a complete anaerobic-aerobic alternating operation mode. For example... Figure 2As shown, each cycle includes, in sequence, an influent stage, an anaerobic reaction stage, an aerobic aeration stage, a settling stage, and a drainage stage. Taking a 4-hour operating cycle as an example, the influent stage lasts 30 minutes, the anaerobic reaction stage lasts 50 minutes, the aerobic aeration stage lasts 150 minutes, the settling stage lasts 5 minutes (taking the period after the 15th day as an example), and the drainage stage lasts 5 minutes. The duration of the anaerobic phase accounts for 15% to 25% of the total cycle time.

[0022] During the aerobic aeration stage, the dissolved oxygen concentration is controlled at 2–4 mg / L, and the apparent airflow velocity is maintained at 1.5–2.5 cm / s, preferably 2.0 cm / s. A moderate aeration intensity ensures the metabolic activity of aerobic microorganisms while providing adequate hydraulic shear force to promote particle surface regularization. Adding readily degradable carbon sources in the anaerobic stage is a key measure to promote granulation. The added carbon source is one or a mixture of sodium acetate and sodium propionate, with sodium acetate being the preferred carbon source. The addition of carbon sources brings the influent chemical oxygen demand (COD) concentration to 300–500 mg / L, creating a substrate-rich environment in the anaerobic stage. This encourages functional microorganisms such as polyphosphate-accumulating bacteria to absorb and store large amounts of carbon as intracellular carbon storage. Once the aerobic stage begins, the external carbon source is largely depleted, and the microorganisms switch to utilizing their intracellular storage for growth and metabolism, forming a typical "abundance-starvation" alternating pattern. This periodic carbon source pulse strategy has a stronger particle-driving force compared to continuous low-concentration influent, and can effectively promote the targeted secretion of protein components in extracellular polymers.

[0023] The protein-to-polysaccharide mass ratio is an important indicator of the degree of granulation completion. Extracellular polymers were extracted using a heating method. Specifically, 10 mL of the sludge mixture sample was placed in a centrifuge tube, heated in an 80℃ water bath for 30 min, and then centrifuged at 4000 r / min for 20 min. The supernatant was collected as the extracellular polymer extract. The protein content in the extracellular polymers was determined using a modified Lowry method, with bovine serum albumin as the standard to plot a standard curve at a wavelength of 750 nm. The polysaccharide content was determined using the phenol-sulfuric acid method, with glucose as the standard to plot a standard curve at a wavelength of 490 nm. As the granulation process progressed, the protein component in the extracellular polymers continuously increased, while the polysaccharide component remained relatively stable. Figure 4As shown, the ratio of protein to polysaccharide gradually increases. The increase in protein components is closely related to the stress response of microorganisms under periodic carbon source pulse stimulation. Proteins have strong hydrophobicity and adhesion ability, and are key skeletal components for maintaining the integrity of particle structure. When this ratio reaches 1.2~1.8, it indicates that a sufficiently dense protein skeletal structure has been formed on the particle surface, and the hydrophobicity and structural strength of the particles have reached the standard of mature particles. At this time, the contact angle measurement value is usually greater than 40°, and the surface Zeta potential tends to stabilize in the range of -15~-25 mV, indicating that granulation is basically completed. During the granulation promotion stage, samples should be taken every 3~5 days for morphological observation. The morphology and surface characteristics of the particles are observed using an optical microscope at 40x magnification. Mature aerobic granular sludge presents a regular spherical or ellipsoidal appearance, with a smooth and dense surface and a uniform yellowish-brown or golden-yellow color. The particle size distribution was determined periodically using the wet sieving method. The mixed liquor sample was sequentially sieved through standard sieves of 2.0 mm, 1.0 mm, 0.5 mm and 0.2 mm, and the dry weight distribution ratio of sludge in each particle size range was statistically analyzed.

[0024] Regarding the specific operations of step three, the stable operation control stage, the goal of this stage is to achieve long-term stable operation of the system after granulation. This invention establishes a dual-parameter monitoring system based on the 30-minute sludge volume index and granulation rate as the core means for stability evaluation and early warning. The 30-minute sludge volume index reflects the overall settling and compressibility performance of the sludge, while the granulation rate reflects the proportion of granular sludge in the total sludge. The granulation rate is determined as follows: a mixed liquor sample is wet-sieved through a 0.2 mm standard sieve; the material remaining on the sieve is granular sludge, and the material passing through the sieve is flocculent sludge. The granulation rate is equal to the percentage of the dry weight of the material remaining on the sieve to the total dry weight of the sludge.

[0025] When the sludge volume index exceeds 80 mL / g or the granulation rate falls below 85% after 30 minutes, the system initiates a stability control program. The control measures include three synergistic adjustments. The first is organic load adjustment, setting the organic load to 2.5–4.0 kg COD / (m³). 3 •d) The appropriate range of organic loading is crucial. Too low an organic loading rate will lead to insufficient microbial nutrition and granule disintegration, while too high an organic loading rate will promote excessive growth of filamentous bacteria, leading to sludge bulking. The second aspect is the adjustment of the carbon-to-nitrogen ratio. Controlling the influent carbon-to-nitrogen ratio within the range of 6-10 ensures a sufficient carbon source supply for the denitrification process, thereby maintaining a stable microenvironment for the anaerobic core within the granules. The third aspect is the regulation of phosphorus release in the anaerobic stage. Maintaining phosphorus release in the anaerobic stage greater than 15 mg / L indicates that the metabolic activity of polyphosphate-accumulating bacteria is at a normal level, and their function as the granule core framework is effectively maintained.

[0026] Selective sludge removal is another important measure to maintain system stability. Specifically, after the settling stage and before effluent discharge, the upper layer of mixed liquor containing flocculent sludge is discharged from the central drain outlet of the reactor, with a discharge volume of 5%–10% of the reactor's effective volume. Since the settling velocity of flocculent sludge is much lower than that of granular sludge (typically 0.5–2.0 m / h for flocculent sludge and 8–25 m / h for mature granular sludge), after the settling stage, the flocculent sludge is mainly distributed in the upper layer of the reactor. The central drain outlet allows for the priority removal of flocculent sludge with a particle size smaller than 0.2 mm. This strategy maintains the volume ratio of granular sludge to flocculent sludge in the system within the range of 7:3 to 8:2. Retaining an appropriate amount of flocculent sludge is beneficial to system operation. Flocculent sludge can effectively capture and adhere free microbial debris and colloidal particles in the aqueous phase, reducing the concentration of suspended solids in the effluent. Simultaneously, it serves as a source of microbial seed for new particle formation, maintaining the system's continuous self-renewal capacity. Selective sludge removal is typically performed 1-2 times daily, with the removal time scheduled within the operating cycle where settling performance is optimal. If the monitoring system detects that the 30-minute sludge volume index exceeds 80 mL / g for three consecutive operating cycles, in addition to the aforementioned control measures, the settling time should be shortened by 1-2 minutes to increase the hydraulic selective pressure, further eliminating loose aggregates with deteriorated settling performance. Simultaneously, the selective sludge removal rate can be appropriately increased to 10%-15% of the reactor's effective volume to accelerate the removal of deteriorated biomass. After the control measures are implemented, the changing trends of both parameters should be continuously monitored. The system typically returns to stable operation within 3-7 days, with the 30-minute sludge volume index falling below the warning threshold and the granulation rate recovering to above 85%.

[0027] The technical effects of the present invention will be further illustrated below through specific embodiments and comparative examples.

[0028] Example 1 represents the optimal design. An acrylic column-shaped sequencing batch reactor (SBR) with an inner diameter of 8 cm, an effective height of 48 cm, an effective volume of 2.4 L, and a height-to-diameter ratio of 6:1 was used. The drain outlet was located at 50% of the reactor's effective height, resulting in a 50% drain ratio. A microporous aeration disc with 60 μm pores was installed at the bottom of the reactor, equipped with a double-layered inclined blade mechanical agitator set at a stirring speed of 80 r / min. Influent was injected from the bottom of the reactor using a peristaltic pump at a flow rate of 60 mL / min. The reactor operating temperature was controlled at 25±1℃ using a constant temperature water bath, and the influent pH was adjusted to 7.0–7.2. Each operating cycle was 4 hours, with 6 cycles per day. The inoculum sludge was taken from the secondary sedimentation tank return sludge of a municipal wastewater treatment plant. Before inoculation, large particulate impurities were removed by filtration through a 0.5 mm screen. The initial MLSS was 3500 mg / L, the initial sludge volume index was 160 mL / g, and the sludge settling ratio was 56%. The influent was artificially prepared simulated domestic sewage, using sodium acetate as the carbon source, with a chemical oxygen demand (COD) concentration of 400 mg / L, ammonia nitrogen concentration of 40 mg / L, total phosphorus concentration of 8 mg / L, and a carbon-to-nitrogen ratio of 10. Trace elements were added according to the standard formula, including calcium chloride, magnesium sulfate, and ferrous sulfate. The settling times for the rapid nucleation induction phase were 18 min for days 1-7, 10 min for days 8-14, and 4 min from day 15 onwards. The specific time allocation for each operating cycle was: 30 min for influent (anaerobic stirring), 50 min for anaerobic reaction (stirring, no aeration), 150 min for aerobic aeration, settling according to the phase, and 5 min for effluent discharge. During the aerobic aeration phase, the dissolved oxygen concentration was controlled at 3.0 mg / L, and the apparent airflow velocity was 2.0 cm / s. On the 7th day of operation, microscopic observation revealed that the sludge flocs began to become denser, showing early signs of aggregation. On day 14, distinct microbial aggregates were observed, with a particle size of approximately 0.3–0.5 mm, and the color changed from initial brownish-yellow to yellowish-brown. On day 21, the protein-to-polysaccharide ratio reached 1.5, the extracellular polymeric protein content was 45 mg / g VSS, and the polysaccharide content was 30 mg / g VSS, with a granulation rate exceeding 85%, indicating that granulation was essentially complete. Figure 3 As shown, during the cultivation process, the sludge volume index (SVI) showed a continuous decreasing trend at 30 min, while the granulation rate showed a continuous increasing trend. The two curves crossed and stabilized around day 21. Continued operation until day 28 resulted in an average particle size of 0.8–1.2 mm, a maximum particle size of 2.5 mm, a stable SVI at 42 mL / g at 30 min, and a MLSS concentration of 6500 mg / L. The dual-parameter monitoring system was then activated to enter the stable operation and control phase. Figure 6As shown, after 180 days of stable operation, the system's 30-minute sludge volume index remained within the range of 38–48 mL / g, the granulation rate remained stable at 89%–93%, the chemical oxygen demand (COD) removal rate remained stable above 96%, the ammonia nitrogen removal rate reached above 98%, the total nitrogen removal rate reached 75%, the total phosphorus removal rate reached above 90%, and the effluent suspended solids concentration was below 15 mg / L. On days 95 and 142, the 30-minute sludge volume index reached the warning threshold of 80 mL / g twice. By timely adjusting the organic load and increasing selective sludge discharge, the system returned to stability within 5 days in both instances.

[0029] Example 2 uses a different carbon source. The reactor configuration and operating parameters are the same as in Example 1, except that sodium propionate is used as the carbon source, with a chemical oxygen demand (COD) concentration of 350 mg / L and a carbon-to-nitrogen ratio of 8. The stepped settling time strategy remains unchanged. Due to the different metabolic pathway of sodium propionate compared to sodium acetate, polyphosphate-accumulating bacteria utilize sodium propionate at a slightly slower rate, resulting in approximately 10% lower phosphorus release in the anaerobic stage compared to Example 1. Significant microbial aggregates were observed on day 16, and the protein-to-polysaccharide ratio reached 1.3 on day 25, with a granulation rate exceeding 85%, indicating complete granulation. The average particle size was 0.6–1.0 mm, and the sludge volume index stabilized at 48 mL / g after 30 minutes. After continuous operation until day 120, the COD removal rate remained stable above 95%, and the total nitrogen removal rate reached 72%.

[0030] Example 3 is a boundary operation scheme. The reactor configuration is the same as in Example 1, except that the operating temperature is controlled at 20±1℃, the influent chemical oxygen demand concentration is reduced to 300 mg / L, the carbon-to-nitrogen ratio is 6, each operating cycle is extended to 6 h, the anaerobic reaction stage lasts 60 min, the aerobic aeration stage lasts 240 min, and the dissolved oxygen concentration is controlled at 2.0 mg / L. The stepped settling time strategy is adjusted to 20 min for days 1-7, 12 min for days 8-14, and 5 min from day 15 onwards. Due to the lower temperature and lower carbon source concentration, the microbial metabolic rate decreases, and the granulation process is correspondingly prolonged. Microbial aggregates are observed on day 19, and the protein-to-polysaccharide ratio reaches 1.2 on day 28, with a granulation rate of 86%, indicating that granulation is complete. The average particle size is 0.5-0.8 mm, and the sludge volume index stabilizes at 55 mL / g after 30 min. After 90 days of continuous operation, the chemical oxygen demand removal rate remained stable at over 95%, and the total nitrogen removal rate reached 70%.

[0031] Comparative Example 1 illustrates a conventional aerobic granular sludge cultivation method. The reactor configuration was identical to that of Example 1, with an inner diameter of 8 cm, an effective height of 48 cm, and an effective volume of 2.4 L. The difference lay in the absence of an anaerobic reaction stage. The operating cycle consisted of 10 min of influent (aeration influent), 200 min of aerobic aeration, 5 min of settling, and 5 min of effluent discharge, for a total cycle time of approximately 220 min plus the settling and effluent discharge times. The settling time was gradually reduced from 30 min on day 1, decreasing by 5 min every 5 days until it reached 5 min on day 30. The influent used sodium acetate as the carbon source, with a chemical oxygen demand (COD) concentration of 400 mg / L, an ammonia nitrogen concentration of 40 mg / L, and a carbon-to-nitrogen ratio of 10. Due to the absence of an anaerobic section, the readily degradable carbon source in the influent was rapidly consumed by fast-growing heterotrophic bacteria under aerobic conditions. Polyphosphate-accumulating bacteria lacked an effective competitive advantage and could not accumulate in large quantities, resulting in a lack of a dense, slow-growing microbial skeleton in the granular core. Small granules began to form on day 25, but were few in number and loosely structured. The granulation rate reached 80% by day 50, and increased to 87% by day 60, where it stabilized. The average particle size was 0.4–0.8 mm, with a less than smooth surface and a relatively loose internal structure. The 30-minute sludge volume index remained stable at 68 mL / g, significantly higher than the 42 mL / g in Example 1. Particle disintegration occurred on day 90, with the 30-minute sludge volume index rising to 95 mL / g and the granulation rate decreasing to 70%. The chemical oxygen demand (COD) removal rate was 93%, while the total nitrogen removal rate was only 48%, significantly lower than the 75% in Example 1. This was attributed to the lack of an alternating anaerobic-aerobic environment, resulting in an incomplete stratified structure of functional microorganisms within the granules and low efficiency in simultaneous nitrification and denitrification.

[0032] Comparative Example 2 illustrates a method without a stepped settling time strategy. The reactor configuration and operating parameters were essentially the same as in Example 1, with an anaerobic reaction stage and pulsed carbon source addition. However, the settling time was fixed at 5 minutes from day 1, without implementing a stepped progression strategy. Due to the excessively short initial settling time and high hydraulic selective pressure, a large amount of activated sludge that had not yet formed aggregates was flushed away within the first 7 days. The MLSS in the reactor dropped sharply to below 800 mg / L, less than 25% of the initial inoculum concentration, resulting in a severe deficiency in system biomass. Although the residual sludge began to aggregate under high selective pressure, and the alternating anaerobic-aerobic environment was conducive to the enrichment of functional microorganisms, the lack of sufficient microbial substrate as particle nuclei led to a significant decrease in the effective collision frequency, resulting in an extremely slow granulation process. The granulation rate was only 65% ​​on day 35 and only reached 82% on day 50. The particles have a loose structure and small size, with an average particle size of only 0.3~0.6 mm. The sludge volume index after 30 min is 72 mL / g, the chemical oxygen demand removal rate is 91%, and the total nitrogen removal rate is 55%. This comparative example fully demonstrates the importance of a stepped settling time strategy for maintaining sufficient biomass in the early stages of cultivation.

[0033] Comparative Example 3 illustrates a method without dual-parameter monitoring and control. The reactor configuration and operating parameters for the first two stages were the same as in Example 1. The stepped settling time strategy and the alternating anaerobic-aerobic operation mode were executed normally. Granulation was completed on day 22, and the initial particle morphology and pollutant removal performance were comparable to Example 1, with a sludge volume index of 45 mL / g at 30 min and a granulation rate of 90%. However, during the subsequent stable operation phase, dual-parameter monitoring and active control were not implemented, and a selective sludge discharge strategy was not adopted; the system relied entirely on natural operation. The system remained in good condition until day 45. However, on day 60, fluctuations in influent water quality led to an occasional increase in organic load to 5.5 kg COD / (m³). 3 ·d), significantly exceeding the upper limit of the suitable range of 4.0 kg COD / (m 3 •d) High load conditions created a favorable environment for the rapid growth of filamentous bacteria, which began to extend outward from the particle surface, resulting in fluffy, filamentous protrusions on the particle surface. Due to the lack of a monitoring and early warning system, operators failed to detect the problem in time and take control measures. By day 75, the filamentous bacteria had proliferated extensively and spread outward from the inside of the particles. The 30-minute sludge volume index increased to 110 mL / g, the granulation rate decreased to 62%, and the system exhibited typical filamentous bulking characteristics. The particle structure became significantly loose, the effluent suspended solids concentration exceeded 50 mg / L, the chemical oxygen demand removal rate dropped to 88%, and the total nitrogen removal rate dropped to 40%. Although attempts were made to remedy the situation by shortening the settling time, the large number of loosened particles could not be restored to a dense structure, and the system essentially lost its granular sludge characteristics after day 90.

[0034] Comparative Example 4 illustrates a method without the addition of an exogenous carbon source. The reactor configuration is the same as in Example 1, with an anaerobic reaction stage and a stepped settling time strategy. The dual-parameter monitoring system is functioning normally, but no readily degradable carbon source such as sodium acetate is added to the anaerobic stage; it relies solely on the existing organic matter in the influent. The simulated domestic wastewater contains a complex organic composition, with rapidly degradable volatile fatty acids accounting for only 15%–25% of the total chemical oxygen demand (COD), while the majority is slow-degrading or recalcitrant organic matter. Due to a severe shortage of carbon sources available for rapid utilization by polyphosphate-accumulating bacteria (PABs) in the anaerobic stage, the intracellular poly(β-hydroxybutyrate) storage is low, with only 2–5 mg of PAB stored per gram of volatile suspended solids (VSS), far below the 15–25 mg / g VSS level in Example 1. The phosphorus release in the anaerobic stage is only 8 mg / L, less than half of the over 20 mg / L in Example 1. The competitive advantage of PPBs cannot be fully established, and the proportion of slowly growing microorganisms in the granular core is low. The extracellular polymeric substance secretion was reduced by approximately 40% compared to Example 1. The lack of protein components resulted in insufficient hydrophobicity of the particle surface, leading to weak adhesion between microorganisms. The protein-to-polysaccharide ratio reached only 0.9 on day 28, failing to meet the granulation threshold of 1.2. The granulation rate was 78% on day 35, with a relatively loose particle structure and noticeable cavities within the particles. The sludge volume index at 30 min was 75 mL / g, the chemical oxygen demand (COD) removal rate was 92%, and the total nitrogen removal rate was 52%. This comparative example demonstrates that the addition of readily degradable carbon sources in the anaerobic stage plays an irreplaceable and crucial role in establishing the competitive advantage of polyphosphate-accumulating bacteria and promoting the secretion of extracellular polymeric protein components.

[0035] The following is a summary of the performance parameters of each embodiment and comparative example, such as Figure 5 The figure shows a comparison of the particle size reduction time and total nitrogen removal rate for each scheme.

[0036] In Example 1, granulation was completed in 21 days, with a 30-minute sludge volume index of 42 mL / g, a granulation rate of 92%, a chemical oxygen demand (COD) removal rate of 96%, a total nitrogen (TNO) removal rate of 75%, and continuous stable operation for 180 days. In Example 2, granulation was completed in 25 days, with a 30-minute sludge volume index of 48 mL / g, a granulation rate of 88%, a COD removal rate of 95%, a TNO removal rate of 72%, and continuous stable operation for 120 days. In Example 3, granulation was completed in 28 days, with a 30-minute sludge volume index of 55 mL / g, a granulation rate of 86%, a COD removal rate of 95%, a TNO removal rate of 70%, and continuous stable operation for 90 days. In Comparative Example 1, granulation was completed in 60 days, with a 30-minute sludge volume index of 68 mL / g, a granulation rate of 87%, a COD removal rate of 93%, a TNO removal rate of 48%, and continuous stable operation for 60 days before dismantling. Comparative Example 2 achieved granulation completion in 50 days, with a 30-minute sludge volume index of 72 mL / g, a granulation rate of 82%, a chemical oxygen demand (COD) removal rate of 91%, and a total nitrogen (TNO) removal rate of 55%. It maintained stable operation for 70 days. Comparative Example 3 achieved granulation completion in 22 days, with a 30-minute sludge volume index rising to 110 mL / g, a granulation rate decreasing to 62%, a COD removal rate decreasing to 88%, and a TNO removal rate decreasing to 40%. It maintained stable operation for 75 days before becoming unstable. Comparative Example 4 achieved granulation completion in over 35 days and was not fully granulated. It achieved a 30-minute sludge volume index of 75 mL / g, a granulation rate of 78%, a COD removal rate of 92%, and a TNO removal rate of 52%. It maintained stable operation for 50 days.

[0037] The detection methods involved in each embodiment and comparative example are described below. Chemical oxygen demand (COD) was determined using the potassium dichromate method according to the national standard GB / T 11914-1989. The specific procedure was as follows: A suitable amount of water sample was placed in a 250 mL Erlenmeyer flask, and potassium dichromate standard solution and concentrated sulfuric acid-silver sulfate solution were added. The mixture was digested at 165℃ for 2 h, then cooled. Titration with ferrous ammonium sulfate standard solution using ferroin as an indicator was performed to the endpoint. COD was calculated based on the amount consumed. Ammonia nitrogen was determined using Nessler's reagent spectrophotometry according to the national standard HJ 535-2009. A standard curve was plotted using ammonium chloride standard solution, and the detection wavelength was 420 nm. Total nitrogen was determined using the alkaline potassium persulfate digestion ultraviolet spectrophotometric method according to national standard HJ 636-2012. After digestion with alkaline potassium persulfate in a high-pressure steam sterilizer at 120℃ for 30 min, the absorbance was measured at wavelengths of 220 nm and 275 nm using an ultraviolet spectrophotometer. Total phosphorus was determined using the ammonium molybdate spectrophotometric method according to national standard GB / T 11893-1989. After digestion with potassium sulfate, ammonium molybdate colorimetric reagent was added, and the absorbance was measured at a wavelength of 700 nm. The concentration of suspended solids and volatile suspended solids in the mixed liquor were determined by gravimetric method, and the samples were dried to constant weight at 105℃ and 600℃, respectively. The sludge volume index was determined according to the national standard CJ / T 51-2018. A 1000 mL sample of the mixed liquor was placed in a graduated cylinder and allowed to stand for 30 min. The volume of sludge after settling was recorded. The sludge volume index is equal to the ratio of the settling volume to the suspended solids concentration of the mixed liquor. The granulation rate was determined using the wet sieving method described above. A 200 mL sample of the homogeneous mixed liquor was passed through a 0.2 mm standard sieve for wet sieving. The oversize and undersize particles were dried at 105℃ to constant weight and then weighed. The granulation rate is equal to the percentage of the dry weight of the oversize particles to the total dry weight. Particle size was determined using a laser particle size analyzer. The mixed liquor was gently stirred before sampling. The measurement range was 0.02–2000 μm. The extraction and detection methods for extracellular polymers have been described in detail above. The settling velocity was determined using the free sedimentation method. A single particle was placed in a graduated cylinder containing water, and the time required for the particle to settle a certain distance was recorded. The settling velocity was then calculated. All test data were calculated as the average of three parallel measurements, and data processing was performed using statistical analysis software.

[0038] This invention achieves rapid cultivation and long-term stable operation of aerobic granular sludge through the organic coupling of three mechanisms: anaerobic-aerobic alternating operation mode, stepwise selective pressure strategy, and dual-parameter linkage regulation. There is a close synergistic relationship among the three mechanisms, which will be analyzed in depth from the three levels of microbial ecology, physicochemistry, and process engineering.

[0039] From a microbial ecological perspective, the core mechanism of the anaerobic-aerobic alternating operation mode lies in providing a competitive advantage to slow-growing microorganisms such as polyphosphate-accumulating bacteria (APBs) and polysaccharide-accumulating bacteria (PSBs) by creating a periodic anaerobic environment. In the anaerobic phase, APBs, particularly *Candidatus Accumulibacter phosphatis*, obtain energy by hydrolyzing intracellular polyphosphates to release phosphate. They then use this energy to absorb volatile fatty acids from the influent and synthesize intracellular polyhydroxyalkanoates, especially poly(β-hydroxybutyrate), for carbon storage. PSBs, particularly *Candidatus Competibacter phosphatis*, obtain energy by hydrolyzing intracellular glycogen accumulated in the aerobic phase. They similarly convert absorbed volatile fatty acids into PSBs for intracellular storage, exhibiting a biphasic coupled metabolic characteristic of glycogen consumption and PSB accumulation. In the aerobic phase, both types of microorganisms oxidize intracellular PSBs as carbon and energy sources for growth and metabolism. APBs simultaneously over-absorb phosphates from the environment to resynthesize polyphosphates, achieving biological phosphorus removal. PSBs, on the other hand, use the energy released from oxidizing PSBs to resynthesize glycogen, completing their metabolic cycle. The dense aggregates formed by these slow-growing microorganisms constitute the skeletal structure of the granule core, with a density and strength far superior to those of the loose aggregates formed by fast-growing heterotrophic bacteria. In the aerobic zone, nitrifying bacteria, including ammonia-oxidizing and nitrite-oxidizing bacteria, enriched on the outer layer of the granules utilize dissolved oxygen to gradually oxidize ammonia nitrogen to nitrate nitrogen. Meanwhile, the interior of the granules, due to limited oxygen diffusion, forms an anaerobic or even anaerobic microenvironment. Denitrifying bacteria utilize intermediate metabolites released by polyphosphate-accumulating bacteria and polysaccharide-accumulating bacteria during the oxidation of intracellular polyhydroxyalkanoates in the aerobic zone as electron donors to complete denitrification. This aerobic-anoxic-anaerobic functional stratification structure of the aerobic granular sludge allows nitrification, denitrification, and phosphorus removal to occur simultaneously within the same granule, achieving synergistic and efficient removal of carbon, nitrogen, and phosphorus. The relative abundance of polyphosphate-accumulating bacteria in the granular sludge cultivated using the method of this invention can reach 15%–25%, far exceeding the typical proportion of 5%–10% in granular sludge cultivated using conventional methods. This is the key microbiological basis for achieving a total nitrogen removal rate of over 70%.

[0040] From a physicochemical perspective, the stepwise selective pressure strategy avoids excessive biomass loss caused by sudden drops in settling time in traditional methods by gradually increasing the hydraulic screening intensity, while simultaneously forming a positive feedback loop with the regulation of extracellular polymer secretion. The longer settling time in the first gradient ensures sufficient microbial substrate for initial aggregation and nucleation. During this stage, microorganisms form primary aggregates through van der Waals forces, hydrogen bonds, and electrostatic interactions. The moderate settling time in the second gradient eliminates loose flocs while creating a competitive environment for the selective growth of dense aggregates. The accelerated secretion of protein components from extracellular polymers in this stage enhances hydrophobic interactions on the aggregate surface, further promoting tight adhesion of microbial particles. The extremely short settling time in the third gradient further strengthens the selective pressure, retaining only mature particles with fast settling rates, accelerating the final completion of the granulation process. The carbon source pulse addition strategy rapidly creates a high-concentration organic carbon environment in the anaerobic zone. This periodic pulse of carbon source concentration stimulates a stress response in microorganisms, significantly promoting the secretion of tightly bound extracellular polymers. Tightly bound extracellular polymers, with their high protein content and strong adhesion, are the core material basis for maintaining the integrity of the three-dimensional structure of particles. In contrast, loosely bound extracellular polymers are easily detached under hydraulic shear and contribute little to the stability of particle structure.

[0041] From a process engineering perspective, the dual-parameter linkage control mechanism provides a reliable engineering guarantee for the long-term stable operation of the system. The 30-minute sludge volume index, as a macroscopic indicator reflecting overall settling performance, has a sensitive early warning capability for system instability. When it rises above the warning threshold of 80 mL / g, it usually indicates that the proportion of loose flocs or filamentous bacteria in the system is beginning to increase. The granulation rate, as a microscopic indicator reflecting the proportion of particles, can accurately identify early signs of particle disintegration. When it drops below 85%, it indicates that the particle breakage rate has exceeded the particle formation rate. The joint monitoring of these two parameters achieves comprehensive stability assessment from macro to micro levels, avoiding misjudgments that may occur with single-parameter monitoring. When either parameter triggers the warning threshold, the system maintains a suitable nutrient supply level for microorganisms through organic load adjustment, ensures sufficient carbon source supply for denitrification through carbon-nitrogen ratio control to maintain a stable microenvironment for the anaerobic core inside the particles through phosphorus release, and maintains and verifies that the metabolic activity of polyphosphate-accumulating bacteria is in a normal state through phosphorus release. Selective sludge removal strategy maintains an appropriate ratio of granular sludge to flocculent sludge. Maintaining approximately 20%–30% flocculent sludge helps capture free microorganisms and colloidal substances to improve effluent quality, and also serves as a source of seed microorganisms for new particle formation, maintaining the system's self-renewal capacity. The results of Comparative Example 3 clearly show that the system lacking dual-parameter monitoring cannot respond promptly to fluctuations in organic load, ultimately leading to large-scale particle disintegration and system collapse. This fully demonstrates the irreplaceable role of active regulation mechanisms in maintaining the long-term stability of aerobic granular sludge systems.

[0042] The above description is only a preferred embodiment of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for rapid cultivation and stable control of aerobic granular sludge based on alternating anaerobic and aerobic operation, characterized in that, Includes the following steps: Step 1, Rapid Nucleation Induction Stage: Activated sludge is inoculated into a sequencing batch reactor (SBR) with an initial sludge concentration of 3000–4000 mg / L MLSS. A stepped settling time strategy is adopted, with settling time controlled at 15–20 min from day 1 to day 7, shortened to 8–12 min from day 8 to day 14, and stabilized at 3–5 min from day 15 onwards. In the influent stage, an anaerobic stirred influent mode is used, with the influent time controlled at 20–40 min, and the dissolved oxygen concentration maintained below 0.2 mg / L, selectively enriching polyphosphate-accumulating bacteria and polysaccharide-accumulating bacteria. Step 2, Granulation Promotion Stage: An alternating anaerobic-aerobic environment is established within each operating cycle. The anaerobic phase lasts for 15%–25% of the cycle time, while the dissolved oxygen concentration is controlled at 2–4 mg / L in the aerobic aeration phase, and the apparent airflow velocity is maintained at 1.5–2.5 cm / s. In the anaerobic phase, readily biodegradable carbon sources are added to achieve a chemical oxygen demand (COD) concentration of 300–500 mg / L. This periodic substrate-rich-deficient alternating pattern promotes extracellular polymer secretion and enhances cell surface hydrophobicity. Granulation is considered basically complete when the protein-to-polysaccharide mass ratio in the sludge reaches 1.2–1.

8. Step 3, Stable Operation Control Phase: Establish a dual-parameter monitoring system based on sludge volume index and granulation rate. When the sludge volume index exceeds 80 mL / g or the granulation rate is below 85% after 30 minutes, stability control is initiated. Control measures include: adjusting the organic load to 2.5~4.0 kg COD / (m³). 3 •d) Control the carbon-nitrogen ratio within the range of 6 to 10 and maintain the phosphorus release in the anaerobic zone greater than 15 mg / L; preferentially discharge flocculent sludge with a particle size of less than 0.2 mm through a selective sludge discharge strategy, and maintain the volume ratio of granular sludge to flocculent sludge within the range of 7:3 to 8:

2.

2. The method according to claim 1, characterized in that, In step one, the height-to-diameter ratio of the sequencing batch reactor is 4:1 to 8:1, the effective volume drainage ratio is 40% to 60%, and the total time for each operating cycle is 4 to 6 hours.

3. The method according to claim 1, characterized in that, In step one, the activated sludge used for inoculation is taken from the return sludge of the secondary sedimentation tank of an urban wastewater treatment plant, and the initial sludge volume index is 120~200 mL / g.

4. The method according to claim 1, characterized in that, In step two, each operating cycle includes the following stages in sequence: water inlet stage, anaerobic reaction stage, aerobic aeration stage, sedimentation stage, and drainage stage. The water inlet stage lasts for 20-40 minutes, the anaerobic reaction stage lasts for 40-60 minutes, and the aerobic aeration stage lasts for 120-180 minutes.

5. The method according to claim 1, characterized in that, In step two, the added readily degradable carbon source is one or a mixture of two of sodium acetate and sodium propionate, and the concentration of the carbon source is 300-500 mg / L based on chemical oxygen demand.

6. The method according to claim 1, characterized in that, In step two, the protein and polysaccharide content in the extracellular polymeric material is detected. The protein content is determined using a modified Lowry method, and the polysaccharide content is determined using a phenol-sulfuric acid method.

7. The method according to claim 1, characterized in that, In step three, the specific operation of the selective sludge discharge strategy is as follows: after the settling stage, the upper layer of mixed liquid containing flocculent sludge is discharged from the drain outlet in the middle of the reactor, with a discharge volume of 5% to 10% of the effective volume of the reactor, while the granular sludge settled at the bottom is retained.

8. The method according to claim 1, characterized in that, In step three, when the sludge volume index exceeds 80 mL / g for three consecutive cycles, the settling time is shortened by 1 to 2 minutes to increase the hydraulic selective pressure.

9. The method according to claim 1, characterized in that, Throughout the entire cultivation process, the reactor operating temperature was controlled at 20~30℃, and the influent pH value was controlled at 6.8~7.

5.

10. The method according to claim 1, characterized in that, The method completes granulation culture within 21-28 days. After culture, the sludge volume index of the granular sludge stabilizes at 35-55 mL / g within 30 minutes, the chemical oxygen demand removal rate reaches over 95%, and the total nitrogen removal rate reaches over 70%.

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