Method for regulating superficial gas velocity to form low-energy consumption aerobic granular sludge

Abstract

The application discloses a method for forming low-energy-consumption aerobic granular sludge by adjusting superficial gas velocity, and adopts a simultaneous nitrogen and phosphorus removal aerobic granular sludge culture device, and the specific operation steps are as follows: step 1, placing activated sludge in the simultaneous nitrogen and phosphorus removal aerobic granular sludge culture device, continuously aerating for 24-48 hours to ensure the activity of the sludge; step 2, using artificial wastewater synthesized by carbon source, nitrogen source and phosphorus source to culture the activated sludge, and using a peristaltic pump to push the artificial wastewater into the reactor from the bottom of the reactor; step 3, performing four processes of simultaneous plug flow water in and out, anaerobic standing, aeration and precipitation in the reactor, and setting a proper superficial gas velocity for the reactor, and continuously culturing under the condition. The application selects a proper superficial gas velocity, provides a good oxidation-reduction environment for the growth of hydrolysis and fermentation bacteria and phosphorus removal functional bacteria, realizes sludge granulation, and improves the removal efficiency of organic matters.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sewage treatment, and relates to a method for forming low-energy-consumption aerobic granular sludge by adjusting apparent gas velocity. BACKGROUND

[0002] The aerobic granular sludge is a dense aggregate with large particle size formed by self-agglomeration of microorganisms in an aerobic state, and has the advantages of smooth surface, high density, good settling performance, high biomass, and impact load resistance, and has great application potential. The formation of the aerobic granular sludge is affected by many factors, including shear force, dissolved oxygen, metal ions, etc., and the shear force (affected by the apparent gas velocity or the dissolved oxygen) is an important parameter for forming the granular sludge. A large number of studies have shown that high shear force is crucial for the formation of the aerobic granular sludge, and therefore a relatively high shear force is often used to cultivate the aerobic granular sludge, resulting in high energy consumption of the system.

[0003] An anaerobic-aerobic alternating operation mode can be used to screen out slow-growing microorganisms with intracellular storage function in the system. Such microorganisms have a low requirement for shear force and have a tendency of spontaneous agglomeration and granulation, so that the high shear force is no longer a necessary condition for the granulation of the aerobic sludge. This feature provides a certain theoretical basis for the formation of the aerobic granular sludge under low energy consumption. In addition, the core microbial population of the aerobic granular sludge, i.e., the slow-growing microorganisms, prefer small-molecule carbon sources (such as volatile fatty acids VFAs), but the content of the small-molecule carbon sources in actual sewage is low, and the macromolecular carbon source is the main body of the carbon source, so there are problems such as difficulty in granulation of sludge, low removal capacity of organic matter and nitrogen and phosphorus in the actual sewage treatment system. SUMMARY

[0004] The present application aims to provide a method for forming low-energy-consumption aerobic granular sludge by adjusting apparent gas velocity, and solves the problem of difficulty in sludge granulation and simultaneous nitrogen and phosphorus removal under the condition of macromolecular carbon source.

[0005] The technical solution adopted by the present application is a method for forming low-energy-consumption aerobic granular sludge by adjusting apparent gas velocity, which uses a simultaneous nitrogen and phosphorus removal aerobic granular sludge cultivation device, and the specific operation steps are as follows:

[0006] Step 1, placing activated sludge in the simultaneous nitrogen and phosphorus removal aerobic granular sludge cultivation device for continuous air exposure for 24-48 h to ensure the activity of the sludge;

[0007] Step 2, using artificial wastewater synthesized by carbon source, nitrogen source and phosphorus source to cultivate the activated sludge, and pushing the artificial wastewater into the reactor from the bottom of the reactor by using a peristaltic pump;

[0008] Step 3, performing simultaneous plug flow water in and out, anaerobic standing, aeration and sedimentation in the reactor, setting an appropriate apparent gas velocity for the reactor, and continuously cultivating under this condition.

[0009] The present application is also characterized in that,

[0010] In step 2, the artificial wastewater is a complex matrix of small molecules and macromolecular organic matters, and 400 mg / L sodium acetate (60%) and soluble starch (40%) are used as carbon sources in terms of COD, 40 mg / L ammonium chloride is used as nitrogen source, and 10 mg / L dipotassium hydrogen phosphate (60%) and potassium dihydrogen phosphate (40%) are used as phosphorus source.

[0011] In step 3, the reactor is operated for 6 cycles per day, and each cycle lasts for 4 hours.

[0012] In step 3, the water is pushed into the reactor from the bottom, and the wastewater is slowly pushed from the bottom of the reactor to the reactor, and the treated water is pushed out through the water outlet by displacement, and the water is pushed in and out at the same time.

[0013] In step 3, the anaerobic standing is performed after the synchronous water in and out is completed, and the reactor is kept in a static state for 30 minutes, so that the system is in a deep anaerobic state.

[0014] In step 3, the aeration is performed after the anaerobic standing is completed, and the aeration unit is started, and the aeration amount is controlled by the rotor flow meter to be 0.26-0.79 L / min, that is, the apparent gas speed is 0.1-0.3 cm·s -1 , and the aeration time is 120-145 min; in the aerobic state, the system performs biological nitrification and aerobic phosphorus absorption, and the synchronous removal of nitrogen and phosphorus is realized.

[0015] In step 3, the sedimentation is performed after the aeration is completed, and the sedimentation time is 30-5 min, and in the cultivation process, the sedimentation time is continuously shortened, and the reduction of the sedimentation time is offset by the aeration time, so that the system operation cycle is 4 hours, and after the sedimentation is completed, the synchronous water in and out of the next cycle is started; the sedimentation time is continuously reduced from 30 min to 5 min in about one month.

[0016] The present application has the beneficial effects that: the method for adjusting the apparent gas speed to form the low-energy-consumption aerobic granular sludge promotes the dominant growth of the filamentous bacteria with hydrolysis and fermentation function, provides a filamentous skeleton for the formation of the granular sludge, and makes the macromolecular carbon source hydrolyzed and fermented into small-molecule carbon sources such as volatile fatty acids, so as to promote the dominant proliferation of the slowly-growing microorganisms with intracellular storage function, and finally form the filamentous aerobic granular sludge. Under the macromolecular carbon source, the low-energy-consumption aerobic granular sludge is formed by using low shear force; a lower apparent gas speed is adopted, and in this process, the redox environment of the carbon source changes, and the metabolic products of the macromolecular carbon source are more easily stored in the intracellular, which is beneficial to the enrichment of a large number of slowly-growing microorganisms, and the stable and good-performance aerobic granular sludge is formed through the synergistic symbiosis between the microbial populations while saving energy consumption. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a structural schematic diagram of the aerobic granular sludge reaction device of the present application;

[0018] Figure 2(a) is a sludge morphology when the aerobic granular sludge system matures;

[0019] Figure 2(b) is a sludge gram staining photo when the aerobic granular sludge system matures;

[0020] Figure 2(c) is a sludge Neisser staining photo when the aerobic granular sludge system matures;

[0021] Figure 2(d) is a settling performance and granulation degree of the aerobic granular sludge system;

[0022] Figure 3 is a VFAs and lactic acid change curve in a typical cycle;

[0023] Figure 4 is a change of intracellular polymers in a typical cycle;

[0024] Figure 5 is a distribution of functional bacteria at the genus level;

[0025] Figure 6(a) is a FISH photo of filamentous bacteria with hydrolysis and fermentation function in the granular sludge;

[0026] Figure 6(b) is a FISH photo of the distribution of filamentous bacteria with hydrolysis and fermentation function in the total bacteria in the granular sludge.

[0027] In the figure, 1. water inlet bucket, 2. water inlet peristaltic pump, 3. water inlet, 4. water outlet, 5. water outlet bucket, 6. water bath water inlet, 7. water bath water outlet, 8. sampling port, 9. aeration pump, 10. glass rotor flowmeter, 11. aeration sand head, 12. time control switch. DETAILED DESCRIPTION

[0028] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0029] The method for forming low-energy-consumption aerobic granular sludge by adjusting the apparent gas velocity of the present application adopts a simultaneous nitrogen and phosphorus removal aerobic granular sludge cultivation device, and the specific operation steps are as follows:

[0030] Step 1, place the activated sludge in the simultaneous nitrogen and phosphorus removal aerobic granular sludge cultivation device, continuously expose to air for 24-48 h, and ensure the activity of the sludge;

[0031] The structure of the simultaneous nitrogen and phosphorus removal aerobic granular sludge cultivation device is shown in Figure 1 and includes a reactor main body, the inner layer of the reactor main body is used for cultivation of the granular sludge, and the reactor main body is connected with water inlet and outlet units and an aeration unit.

[0032] The reactor bottom is provided with a water inlet 3, and two layers of water distribution nets are arranged above the water inlet 3. A plurality of sampling ports 8 are arranged on the inner layer longitudinal axis. The reactor upper portion is provided with a water outlet 4. The outer layer of the reactor is kept warm by a water bath, and the reactor temperature is maintained at (20±1)℃. The lower portion of the outer layer is connected with a water bath inlet 6, and the upper portion is connected with a water bath outlet 7. The water bath inlet 6 is connected with a constant temperature water bath device through a pipeline. The circulating water is circulated through the outer layer of the reactor in a low-in high-out mode to keep the reactor warm. The main body of the reactor is a sequencing batch reactor (SBR) with equal working volume.

[0033] The water inlet unit comprises a water inlet bucket 1 connected with a peristaltic pump 2 through a water inlet pipeline. The peristaltic pump 2 is controlled by a time control switch 12. The water inlet pipeline of the peristaltic pump 1 is connected with the water inlet 3 of the reactor. The aeration unit comprises an air compressor connected with the time control switch 12 on one side and connected with a rotor flow meter 10 on the other side. The bottom of the reactor is connected with an aeration head. The aeration head is connected with an aeration head 11 through the bottom end of the aeration pipe. The air compressor is an electromagnetic air compressor, and the aeration head 11 is a sand core aeration head. The water outlet unit comprises a water outlet bucket 5 connected with the water outlet 4 at the top end of the reactor through a water outlet pipeline.

[0034] Step 2: The artificial wastewater synthesized by using carbon source, nitrogen source and phosphorus source is used to cultivate activated sludge. The artificial wastewater is pushed into the reactor from the bottom of the reactor by the peristaltic pump 2. The artificial wastewater is a complex substrate of small molecules and macromolecular organic matter. The carbon source is 400mg / L sodium acetate (60%) and soluble starch (40%) in terms of COD. The nitrogen source is provided by 40mg / L ammonium chloride, and the phosphorus source is provided by 10mg / L dipotassium hydrogen phosphate (60%) and potassium dihydrogen phosphate (40%).

[0035] Step 3: The four processes of synchronous push flow water inlet and outlet, anaerobic standing, aeration and sedimentation are carried out in the reactor. The reactor is set to an appropriate superficial gas velocity. The reactor is continuously cultured under the condition. The reactor is operated for 6 cycles per day, and each cycle is 4h.

[0036] The synchronous water inlet and outlet adopt bottom push flow water inlet. The water inlet is 2L and takes 60min. The wastewater is slowly pushed from the bottom of the reactor to the reactor. The treated water is pushed out through the water outlet 4 by replacement. The water inlet and outlet are carried out synchronously.

[0037] Anaerobic standing: after the synchronous water inlet and outlet are completed, the reactor is kept in a stationary state for 30min. The reactor is kept in a stationary state, so that the system is in a deep anaerobic state, which is beneficial to achieve certain denitrification and anaerobic phosphorus release. At the same time, under the condition of macromolecular carbon source, the bacteria with storage function hydrolyze and ferment organic matter, store it in the cell to form poly-β-hydroxyalkanoate (PHAs) and glycogen;

[0038] Aeration, after anaerobic standing, open the aeration unit to provide aerobic conditions for the system. The aeration rate is controlled by the rotor flowmeter 10 at 0.26-0.79 L / min, i.e. the apparent gas velocity is 0.1-0.3 cm·s -1 , the aeration time is 120-145 min; under aerobic conditions, the system can carry out nitrification and aerobic phosphorus uptake, and realize the simultaneous removal of nitrogen and phosphorus.

[0039] Precipitation, after aeration, precipitate for 30-5 min, and during the cultivation process, the precipitation time is continuously shortened, and the reduction of the precipitation time is offset by the aeration time to ensure that the operation cycle of the system is stable at 4 h. After precipitation, the simultaneous water in and out of the next cycle is realized. In order to further promote the granulation of sludge, the sludge retention rate in the system is ensured by continuously adjusting the precipitation time and the drainage ratio to promote the granulation of sludge. The precipitation time is continuously reduced from 30 min to 5 min in about one month. At the beginning, a longer precipitation time is used to ensure the enrichment of functional bacteria and effectively retain them in the system.

[0040] The present application cultivates aerobic granular sludge with simultaneous nitrogen and phosphorus removal. The double-layer water distribution net arranged at the bottom of the reactor enables the uniform distribution of the influent at the bottom and inhibits the occurrence of short flow phenomenon, and controls the number of filamentous bacteria in the system within a certain range.

[0041] Under complex carbon source conditions, the setting of the apparent gas velocity is related to the hydrolysis and fermentation of macromolecules. Selecting a suitable apparent gas velocity has three effects: (1) promoting the dominant growth of filamentous bacteria with hydrolysis and fermentation function to provide filamentous skeleton for the formation of granular sludge; (2) hydrolyzing and fermenting macromolecular carbon sources into small molecular carbon sources such as volatile fatty acids to promote the dominant proliferation of slowly growing microorganisms with intracellular storage function; and (3) greatly reducing energy consumption.

[0042] Example 1

[0043] The method for adjusting the apparent gas velocity to form low-energy-consumption aerobic granular sludge of the present application uses a simultaneous nitrogen and phosphorus removal aerobic granular sludge cultivation device, and the specific operation steps are as follows: inoculating flocculent sludge into the reactor, the flocculent sludge is the backflow sludge of a municipal sewage treatment plant. The sludge is mainly in the form of flocs, the structure is loose, the settling performance is poor, and there are many filamentous bacteria. The retrieved sludge is filtered by a sieve with a pore size of 1 mm, and the impurities are removed before being moved into the reactor. The cultivation is carried out by using the cultivation method provided by the present application, and the granular sludge system completes granulation at the end of the operation and stably operates for more than two months.

[0044] The reactor material is organic glass, the reactor is 110 cm high, the inner diameter is 7.5 cm, the effective water depth is 92 cm, and the height-diameter ratio is 12.27. The effective volume of the reactor is 4 L, and the drainage ratio is set to 50%. The aeration amount is set to 0.26-0.79 L / min by the rotor flowmeter 10, that is, the apparent gas velocity is 0.1-0.3 cm·s -1 The reactor is controlled by a time control switch 12 to control water inflow and outflow and aeration, and a constant-temperature water bath system is used to keep the reactor operating at (20±1) ℃.

[0045] At the end of the reactor operation, as shown in Fig. 2(a), the system is mainly composed of granular sludge, the particle size of the granular sludge is relatively uniform, the settling property is good, SVI 30 and SVI 30 / SVI5 are 43 mL·g -1 , 1, as shown in Fig. 2(d), but the particle boundary is not clear, the shape is irregular, and there are many filamentous bacteria.

[0046] As shown in Fig. 2(b) and Fig. 2(c), the gram staining and the nassier staining at this stage further verify that the shape of the granular sludge is irregular, the types of filamentous bacteria are various, and the filamentous bacteria penetrate through the granular sludge, and it can be seen that the sludge of the system is formed in the form of granular sludge by the filamentous bacteria as the skeleton and the growth of the zoogloea bacteria.

[0047] Example 2

[0048] Performance of the aerobic granular sludge system on pollutant removal: The performance of the sludge on pollutant removal is evaluated by the removal effects of COD and nitrogen and phosphorus. The granular sludge absorbs volatile fatty acids in the wastewater in the anaerobic stage, and stores them in the form of organic particles such as poly-β-hydroxyalkanoate (PHA) in the cells, and in the aerobic stage, polyhydroxyalkanoate accumulated in the body during anaerobic is used as carbon source and energy for bacterial growth and reproduction. In this process, COD and nitrogen and phosphorus can be removed to a certain extent.

[0049] As for the macromolecular carbon source in the present application, the system will first carry out hydrolysis and fermentation of the macromolecular carbon source, and the selection of the apparent gas velocity will determine whether the macromolecular carbon source can be completely utilized. The use of appropriate apparent gas velocity will promote the growth of hydrolysis and fermentation bacteria, promote the hydrolysis and fermentation of macromolecular carbon source into small molecular carbon source, and accelerate the carbon source uptake rate. At the same time, it can also increase the anoxic-anaerobic zone inside the granular sludge, promote the proliferation of denitrifying bacteria, and achieve good simultaneous nitrification and denitrification and denitrification phosphorus removal.

[0050] During system operation, an appropriate apparent gas velocity not only reduces energy consumption but also provides excellent COD removal efficiency. The COD removal rate in the system is above 80%. Under the cultivation conditions based on the operating parameters of this invention, the total nitrogen removal rate in the effluent remains consistently high, at 64.4%. The phosphorus removal rate is above 95% throughout the entire operation period, stabilizing at approximately 98% towards the end of the reactor's operation.

[0051] Example 3

[0052] Metabolic characteristics of granular sludge: The aerobic granular sludge with good nitrogen and phosphorus removal efficiency obtained through the above examples was further investigated to study the granular sludge's ability to utilize carbon sources and the acid-producing ability of the hydrolytic fermentation bacteria. Large-molecule carbon sources are usually difficult for microorganisms to utilize and require hydrolysis and fermentation to produce small-molecule carbon sources. The degree of hydrolysis and fermentation is then reflected in the acid-producing ability of the hydrolytic fermentation bacteria.

[0053] like Figure 3 As shown, the changes in VFAs and lactic acid in the reactor during a typical cycle are illustrated. Acetic acid was not detected in the first 30 minutes after influent intake, indicating a high utilization rate of acetic acid. Acetic acid accumulation begins at 30 minutes, suggesting that an appropriate apparent gas velocity facilitates the hydrolysis and fermentation of macromolecular carbon sources, leading to the production of more VFAs. Subsequently, the produced VFAs are gradually taken up by the microorganisms, and their concentration decreases. Regarding lactic acid, during the anaerobic phase, the lactic acid concentration increases continuously within 15 minutes, reaching its maximum at 15 minutes, and then decreases continuously. It further decreases during the aerobic phase, eventually reaching a concentration of 0.20 mg / L. -1 .

[0054] The results showed that an appropriate apparent gas velocity would promote the hydrolysis and fermentation of macromolecular carbon sources to produce more small molecule organic matter such as VFAs. Among them, lactic acid was produced quickly and utilized at a high rate, with almost no lactic acid residue at the end of the aerobic phase.

[0055] In this invention, the alternating anaerobic-aerobic operation mode is mainly used to cultivate slow-growing microorganisms with storage capacity. These microorganisms, during the anaerobic stage, take up and store external carbon sources intracellularly, synthesizing PHB and PHV for their own growth and reproduction during the aerobic stage. For example... Figure 4 The figure shows the changes in PHB, PHV, and glycogen during a typical cycle. During the anaerobic phase, the system absorbs extracellular VFAs and stores them intracellularly to synthesize PHB and PHV, with concentrations of 23.85 mg / g VSS. -1 and 0.11 mg·gVSS -1 The amount of glycogen degradation was 24.78 mg·gVSS. -1 .

[0056] In the aerobic stage, PAOs can use oxygen as an electron acceptor for phosphorus uptake, while degrading PHAs to provide energy and carbon source, part of which is used for glycogen synthesis. The PHAs (sum of PHB and PHV) consumption of the system is 25.53 mg·gVSS -1 , and the PHAs consumption of the system in the aerobic stage is large under the appropriate superficial gas velocity. In addition, the maximum glycogen synthesis in the reactor is 26.65 mg·gVSS -1 . This shows that under the condition of macromolecular carbon source, the appropriate superficial gas velocity can promote the hydrolysis and fermentation process of macromolecular carbon source, and the carbon source is stored intracellularly in the anaerobic stage, and the extracellular carbon source is less in the aerobic stage, so the microorganisms use intracellular carbon source for growth and reproduction. The system is more likely to experiment with the anaerobic satiation-aerobic utilization of carbon source metabolic model, thus facilitating the granulation of sludge and stable operation of the system.

[0057] Example 4

[0058] Microbial community structure of granular sludge: The microbial community structure of the sludge was analyzed by 16S rRNA gene high-throughput sequencing technology. As shown in Figure 5 , the proportion of functional bacteria at the genus level is shown.

[0059] In the macromolecular carbon source system, a filamentous bacteria with hydrolysis and fermentation of macromolecular organic matter was found, which belongs to the Chloroflexi phylum, and the content of the hydrolysis and fermentation type filamentous bacteria increases continuously with the continuous operation of the system, and the highest abundance reaches 10.44%. This shows that under the condition of complex carbon source, the appropriate superficial gas velocity can promote the generation of hydrolysis and fermentation filamentous bacteria, so that the slowly growing microorganisms can use the organic acids produced by the hydrolysis and fermentation of filamentous bacteria for their own growth and reproduction. At the same time, Candidatus Competibacter, a traditional polysaccharide bacteria, was also found in the system, which can produce energy by glycolysis of glycogen in the anaerobic stage and store VFA as PHAs, and oxidize PHAs to produce energy in the aerobic stage for glycogen synthesis. The abundance of Candidatus Competibacter in the system increases continuously, which is mainly due to the fact that the appropriate superficial gas velocity provides sufficient VFA for this bacteria, which is beneficial to its attachment growth on the hydrolysis and fermentation filamentous bacteria, and thus promotes the granulation of sludge, which corresponds to the results of the staining photos in Example 1. It is speculated that the filamentous bacteria with hydrolysis and fermentation are easy to reproduce only when there is a lot of macromolecular carbon source (such as soluble starch). At the same time, the appropriate superficial gas velocity provides favorable conditions for the growth of hydrolysis and fermentation filamentous bacteria and the hydrolysis and fermentation of macromolecular carbon source, and on the other hand, it provides a filamentous skeleton for granular sludge, forming a symbiotic system of filamentous bacteria and slowly growing microorganisms.

[0060] The dominant proliferation of Candidatus Competibacter at the end of the reactor operation is consistent with the higher anaerobic PHAs synthesis and aerobic glycogen synthesis in the reactor in Example 3. In addition, according to the change rule of the system hydrolysis fermentation products and intracellular storage, it is speculated that the appropriate superficial gas velocity will affect the redox environment, produce more hydrolysis fermentation products to provide small molecule carbon source for the growth of Candidatus Competibacter.

[0061] In order to further verify that the hydrolysis and fermentation filamentous bacteria provide filamentous skeleton for granular sludge, the relative quantity and spatial distribution of hydrolysis and fermentation filamentous bacteria in granular sludge at the end of the reactor are analyzed by fluorescence in situ hybridization (FISH) technology. As shown in FIG. 6(a) and FIG. 6(b), the hydrolysis and fermentation filamentous bacteria account for a large proportion in the system, and in the form of skeleton throughout the granular sludge. The system uses hydrolysis and fermentation filamentous bacteria as skeleton, uses its own hydrolysis and fermentation function to provide small molecule fermentation products for other slow-growing microorganisms with intracellular storage function, forms a symbiotic system, and forms stable granular sludge.

Claims

1. A method for adjusting apparent gas velocity to form low-energy-consumption aerobic granular sludge, employing a simultaneous denitrification and phosphorus removal aerobic granular sludge cultivation device, characterized in that... The specific steps are as follows: Step 1: Place the activated sludge in a simultaneous denitrification and phosphorus removal aerobic granular sludge cultivation device and continuously aerate it for 24-48 hours to ensure sludge activity. Step 2: Artificial wastewater synthesized using carbon, nitrogen, and phosphorus sources is used to cultivate activated sludge. The artificial wastewater is pushed into the reactor from the bottom of the reactor by a peristaltic pump (2). Step 3 involves four processes in the reactor: simultaneous plug flow in and out, anaerobic settling, aeration, and sedimentation. An appropriate apparent gas velocity is set for the reactor, and the reactor is continuously cultured under these conditions. In step 2, the artificial wastewater uses a composite matrix of small and large molecular organic matter, with sodium acetate (COD 400 mg / L) and soluble starch as carbon sources, nitrogen source provided by ammonium chloride (40 mg / L), and phosphorus source provided by dipotassium hydrogen phosphate (10 mg / L) and potassium dihydrogen phosphate. In step 3, the synchronous water inlet and outlet adopts bottom push flow water inlet. The water inlet of 2 L takes 60 min. The sewage is slowly pushed from the bottom of the reactor to the reactor. The treated water is pushed out through the outlet (4) by displacement. The water inlet and outlet are carried out simultaneously. In step 3, after the anaerobic settling is completed and the synchronous inflow and outflow are finished, the reactor is kept in a static state for 30 minutes. The reactor settling allows the system to be in a deep anaerobic state. In step 3, after aeration and anaerobic settling, the aeration unit is turned on, and the aeration rate is controlled by the rotor flow meter (10) at 0.26 ~ 0.79 L / min, that is, the apparent gas velocity is 0.1 ~ 0.3 cm·s. -1 The aeration time is 120 min to 145 min; under aerobic conditions, the system carries out biological nitrification and aerobic phosphorus uptake to achieve simultaneous removal of nitrogen and phosphorus. In step 3, after aeration, the sedimentation time is 30 min to 5 min. During the cultivation process, the sedimentation time is continuously shortened, and the reduction in sedimentation time is offset by the reduction in aeration time, ensuring that the system's operating cycle is stable at 4 hours. After sedimentation, the next cycle of synchronous inflow and outflow is completed. The sedimentation time is continuously reduced from 30 min to 5 min over a period of about one month.

2. The method for adjusting apparent gas velocity to form low-energy aerobic granular sludge according to claim 1, characterized in that, The reactor in step 3 runs for 6 cycles per day, with each cycle lasting 4 hours.

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