A method for culturing granular sludge

Abstract

The embodiment of the present application provides a method for culturing granular sludge, comprising: a stable preparation step: continuously flowing wastewater with a first COD concentration into the UASB reactor through an inlet at a fixed flow rate, so that the microbial activity of the anaerobic digestion sludge contained in the UASB reactor reaches a stable state, wherein the organic load of the UASB reactor in the stable preparation step is a first organic load; a granular sludge domestication step: adjusting a peristaltic pump, so that the UASB reactor operates at a second organic load in the first half of a single domestication period and operates at 0 organic load in the second half of the single domestication period, wherein the second organic load is twice the first organic load, and the granular sludge domestication step consists of multiple domestication periods, and the granular sludge cultured by the method is more efficient than that of a traditional method in the prior art.

Description

A method for cultivating granular sludge Technical Field

[0001] This application relates to the field of wastewater treatment technology, and in particular to a method for cultivating granular sludge. Background Technology

[0002] Global climate change has become a major challenge facing humanity in the 21st century. Since the Industrial Revolution, greenhouse gas emissions, primarily due to human activities, have surged, causing the global average temperature to rise by approximately 1.1°C, threatening human survival. Against this backdrop, reducing greenhouse gas emissions, promoting energy structure transformation, and developing a circular economy have become international consensus. Among these efforts, the resource utilization of organic waste is a crucial pathway to achieving carbon neutrality. Anaerobic digestion is a biological process that converts organic matter into biogas through microbial metabolism under anaerobic conditions. This technology combines pollution control and energy recovery, making it a powerful method for achieving dual-carbon goals.

[0003] Traditional anaerobic activated sludge processes suffer from problems such as loose structure, poor settling performance, and low sludge concentration in the aeration tank, resulting in limited system treatment efficiency and susceptibility to shock loads. In contrast, anaerobic granular sludge effectively prevents sludge loss, extends sludge retention time, and ensures stable operation of the UASB reactor under high loads.

[0004] Currently, the cultivation time for anaerobic granular sludge using activated sludge as inoculum is lengthy, leading to numerous problems in the practical application of granular sludge technology, such as increased operating costs and the inability to meet effluent quality standards during startup. Therefore, accelerating the granulation process of flocculent sludge and realizing the large-scale application of anaerobic granular sludge technology has become a key concern in the industry. Summary of the Invention

[0005] This application provides a method for cultivating granular sludge to solve the technical problem of low cultivation efficiency of anaerobic granular sludge in the prior art.

[0006] In a first aspect, embodiments of this application provide a method for cultivating granular sludge. The method utilizes a UASB reactor system, which includes a UASB reactor, an inlet pipe, and a peristaltic pump. The UASB reactor has an inlet at its bottom, which is connected to an external wastewater source via the inlet pipe. The peristaltic pump, used to regulate the inlet flow rate, is installed on the inlet pipe. The UASB reactor has an outlet at its upper part. The UASB reactor contains anaerobic digested sludge. The method is characterized by the following steps:

[0007] Stabilization preparation step: Wastewater with a first COD concentration is continuously fed into the UASB reactor through the inlet at a fixed flow rate, so that the activity of the microorganisms containing the anaerobic digested sludge in the UASB reactor reaches a stable state, wherein the organic load of the UASB reactor in the stabilization preparation step is the first organic load.

[0008] Granular sludge acclimatization step: Adjust the peristaltic pump so that the UASB reactor operates at a second organic load in the first half of a single acclimatization cycle and at a zero organic load in the second half of a single acclimatization cycle, wherein the second organic load is twice the first organic load, and the granular sludge acclimatization step consists of multiple acclimatization cycles.

[0009] In one possible implementation, prior to the stable operation step, the method further includes:

[0010] Startup steps:

[0011] Wastewater with a second COD concentration is continuously fed into the UASB reactor through the inlet at a fixed flow rate;

[0012] Starting with the second COD concentration, the COD concentration of the wastewater flowing into the UASB reactor is gradually increased over time.

[0013] The COD removal rate of the UASB reactor for wastewater with different COD concentrations was measured.

[0014] The COD concentration of the wastewater with the highest COD removal rate by the UASB reactor is determined as the first COD concentration.

[0015] In one possible implementation, the anaerobic digested sludge is activated sludge enriched with hydrotrophic methanogens.

[0016] In one possible implementation, the first COD concentration is 2000 mg / L.

[0017] In one possible implementation, the pH of the wastewater with a first COD concentration flowing into the UASB reactor is 7-8.

[0018] In one possible implementation, the volume of anaerobic digested sludge contained in the UASB reactor is 1 / 2 of the UASB reactor volume.

[0019] In one possible implementation, the UASB reactor is provided with a tube body and a sludge hopper, the sludge hopper is located below the tube body, the inlet is located in the sludge hopper, the tube body includes an inner tube and an outer tube, the inner tube and the outer tube are separated by an insulation layer, the inner tube contains the main reaction chamber, and the upper part of the UASB reactor is provided with an exhaust port and an outlet.

[0020] In one possible implementation, the temperature of the insulation layer is 37±1℃.

[0021] In the method for cultivating granular sludge proposed in the embodiments of this application, experiments have shown that the method for cultivating anaerobic granular sludge is more efficient than the traditional method. Attached Figure Description

[0022] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0023] Figure 1 is a schematic diagram of the structure of a UASB reactor system provided in an embodiment of this application;

[0024] Figure 2 is a flowchart illustrating a method for cultivating granular sludge according to an embodiment of this application;

[0025] Figure 3 is a graph showing the effect of COD concentration changes in the influent and effluent of the UASB reactor during the startup steps provided in the embodiments of this application.

[0026] Figure 4 is a comparison of the COD removal rate between the wastewater treatment method based on the UASB reactor provided in the embodiments of this application and the comparative example.

[0027] Figure 5 is a comparison of the gas production of the wastewater treatment method based on the UASB reactor provided in the embodiments of this application and the gas production of the UASB reactor in the comparative example.

[0028] Figure 6 is a comparison of the methane content in the gas produced by the wastewater treatment method based on the UASB reactor provided in the embodiments of this application and the comparative example of the UASB reactor.

[0029] Figure 7 is a comparison diagram of the sludge TSS and VSS of the UASB reactor sludge provided in the embodiments of this application with those of the comparative example.

[0030] Figure 8 is a comparison of the particle size of sludge from the UASB reactor in the embodiment of this application with that of the comparative example.

[0031] Figure 9 shows the method for cultivating granular sludge provided in the embodiments of this application and the sludge settling velocity of the UASB reactor in the comparative example.

[0032] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concepts of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0033] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of systems and methods consistent with some aspects of this application as detailed in the appended claims.

[0034] Currently, the cultivation time for anaerobic granular sludge using activated sludge as inoculum is long, which brings many problems to the practical application of granular sludge technology, such as increased operating costs and the inability of effluent quality to meet standards during start-up. Therefore, how to improve the granulation efficiency of flocculent sludge has become a concern in the industry.

[0035] Please refer to Figure 1, which is a schematic diagram of the structure of a UASB reactor system provided in one embodiment of this application. The system includes a UASB reactor 1, an inlet pipe 2, and a peristaltic pump 3. An inlet 121 is provided at the bottom of the UASB reactor 1. The UASB reactor 1 is provided with a pipe body 11 and a sludge hopper 12. The sludge hopper 12 is located below the pipe body 11. Optionally, the sludge hopper is funnel-shaped. The inlet 121 can be specifically located at the bottom of the sludge hopper 12. The inlet 121 is connected to an external wastewater source through the inlet pipe 2. The inlet pipe 2 is equipped with a peristaltic pump 3 for controlling the inlet flow rate. The main reaction chamber is located inside the pipe body 11. The upper part of the UASB reactor is provided with an exhaust port 13 and an outlet 14. Further, the pipe body 11 may include an inner pipe 111 and an outer pipe 112. The main reaction chamber is located inside the inner pipe 111, and an insulation layer 113 is located between the inner pipe 111 and the outer pipe 112. The upper part of the UASB reactor is provided with an exhaust port 13 and an outlet 14. The UASB reactor 1 contains anaerobic digested sludge. In this embodiment, the inlet flow rate can be adjusted by the peristaltic pump 3, thereby adjusting the organic load of the UASB reactor within a certain time period, such as 1 hour or 12 hours.

[0036] Please refer to Figure 2, which is a schematic flow diagram of a method for cultivating granular sludge according to an embodiment of this application. The method utilizes the UASB reactor system shown in Figure 1 and includes the following steps:

[0037] S201: Startup Steps:

[0038] Wastewater with a second COD (Chemical Oxygen Demand) concentration is continuously fed into the UASB reactor at a fixed flow rate through the inlet; starting with the second COD concentration, the COD concentration of the wastewater flowing into the UASB reactor is gradually increased over time; the COD removal rate of the UASB reactor for wastewater with different COD concentrations is measured; the wastewater COD concentration with the highest COD removal rate by the UASB reactor is determined as the first COD concentration.

[0039] For example, please refer to Figure 3, which shows the effect of COD concentration changes in the influent and effluent of the UASB reactor during the start-up process provided in this embodiment. The COD concentration of the UASB reactor influent was increased from 1000 mg / L to 3000 mg / L in 200 mg / L intervals. Initially, the COD concentration of the effluent from the UASB reactor showed a decreasing trend when the influent COD concentration was increased. This is mainly attributed to the fact that during the anaerobic digestion process in the UASB reactor, the functional microbial community needs a certain period of acclimatization to adapt to the system environment, thereby gradually restoring its metabolic activity and treatment efficiency. After a period of operation, when the influent COD concentration was 2000 mg / L, the COD concentration of the UASB reactor effluent was about 200 mg / L, and the removal rate reached 90%, which is the organic load condition with the highest removal rate in the entire start-up phase. By gradually increasing the influent COD concentration, an upward trend in the effluent COD concentration of the UASB reactor can be observed. When the influent COD concentration reaches 3000 mg / L, the effluent COD concentration of the UASB reactor is approximately 430 mg / L, with a removal rate of about 85%, and the system gradually stabilizes. 2000 mg / L can be set as the initial COD concentration. To prevent system collapse and acidification during subsequent experiments with different feed methods, subsequent experiments will be conducted under the organic loading conditions that optimize reactor performance.

[0040] It should be noted that step S201 is an optional step, and an empirical value can be selected as the first COD concentration, and the process can proceed directly to S202.

[0041] S202: Stabilization preparation steps:

[0042] Wastewater with a first COD concentration is continuously fed into the UASB reactor at a fixed flow rate through the inlet to stabilize the activity of the microorganisms containing the anaerobic sludge within the reactor. The organic load of the UASB reactor in this stabilization preparatory step is the first organic load. Specifically, when the COD removal rate in the effluent stabilizes at a certain value within a preset time window, the activity of the microorganisms containing the anaerobic sludge in the UASB reactor is considered to have reached a stable state. System operation data shows that the anaerobic digestion process gradually returns to a stable operating state. This indicates that the functional microbial community within the UASB reactor has completed its adaptive acclimatization to the influent COD load, thereby driving the reaction system into a stable operating state and providing a good operational foundation for subsequent process optimization.

[0043] S203: Granular sludge acclimation step: Adjust the peristaltic pump to change the flow rate of wastewater entering the UASB reactor, so that the UASB reactor operates at the second organic load in the first half of a single acclimation cycle and at zero organic load in the second half of a single acclimation cycle. The second organic load is twice the first organic load. The granular sludge acclimation step consists of multiple acclimation cycles. The granular sludge acclimation step is the process of granulating flocculent anaerobic digested sludge.

[0044] For example, a single cycle is set to 24 hours. In the first half of the cycle, i.e. the first 12 hours, the wastewater is introduced into the UASB reactor at a flow rate four times that in the stabilization preparation step. In the second half of the cycle, i.e. the last 12 hours, the wastewater is stopped from entering the UASB reactor. The granular sludge acclimation step consists of multiple acclimation cycles. Preferably, the granular sludge acclimation step consists of 40 days.

[0045] Preferably, the anaerobic digestion sludge is activated sludge enriched with hydrotrophic methanogenic bacteria.

[0046] Preferably, the temperature of the insulation layer is 37±1℃.

[0047] Preferably, the first COD concentration is 2000 mg / L.

[0048] Preferably, the pH of the wastewater flowing into the UASB reactor is 7-8.

[0049] Preferably, the volume of anaerobic digested sludge contained in the UASB reactor is 1 / 2 of the UASB reactor volume.

[0050] The following describes the experimental results of the embodiments and comparative examples of this application.

[0051] Example

[0052] The system of this invention (as shown in Figure 1) is placed in the Environmental Chemistry and Science Laboratory of the Central Campus of Shenyang University of Technology to implement the method described in the embodiments of this invention.

[0053] The specific implementation method is as follows:

[0054] The sludge used for laboratory inoculation was activated sludge enriched with hydrotrophic methanogens. The total suspended solids (TSS) concentration in the mixed liquor was 24.5 g / L, and the volatile suspended solids (VSS) concentration was 15.5 g / L. The VSS / TSS ratio was 0.63, and the initial settling velocity was 59.4 m. The experimental wastewater was synthetic organic wastewater with a COD:N:P ratio of 200:5:1 and a pH of 7. Table 1 shows the composition, concentration, and supplier of the synthetic organic wastewater used in this application.

[0055] Table 1

[0056] Component Concentration Supplier: Peptone 0.80 g / L, Shenyang Tiexi District Chemical Reagent Factory; Beef Extract 0.50 g / L, Shenyang Tiexi District Chemical Reagent Factory; Glucose 0.40 g / L, Shenyang Tiexi District Chemical Reagent Factory; K₂HPO₄ 0.40 g / L, Shenyang Tiexi District Chemical Reagent Factory; NH₄Cl 0.1 g / L, Shenyang Tiexi District Chemical Reagent Factory; CaCl₂ 0.05 g / L, Shenyang Chemical Co., Ltd.; MgCl₂ 0.04 g / L, Shenyang Chemical Co., Ltd.; FeSO₄ 0.02 g / L, Shenyang Tiexi District Chemical Reagent Factory; Zinc Sulfate 0.00037 mol / L, Shenyang Tiexi District Chemical Reagent Factory; Manganese Sulfate 0.0025 mol / L, Shenyang Chemical Co., Ltd.; Copper Sulfate 0.00014 mol / L, Shenyang Chemical Co., Ltd.; Cobalt Chloride 0.0084 mol / L, Shenyang Chemical Co., Ltd.; Nickel Chloride 0.00025 mol / L, Shenyang Chemical Co., Ltd.; Boric Acid 0.0008 mol / L, Shenyang Tiexi District Chemical Reagent Factory; EDTA 0.0034 mol / L, Liaoning Guangfu Fine Chemical Research Institute. surface

[0057] Please refer to Figure 1. Wastewater enters through inlet 121, is treated, and then discharged through outlet 14. Influent water samples are collected from the wastewater source, effluent water samples are collected from outlet 14, gas samples are collected from exhaust port 13, and sludge samples are collected from sludge sampling port 15. A water bath insulation layer 113 is installed in the middle of the UASB reactor to control the reactor temperature at 37±1℃.

[0058] The entire study was divided into three stages: UASB reactor start-up, Stage 1 stabilization preparation, Stage 2 granular sludge acclimation, and Stage 3 stabilization recovery. COD removal rate is one of the core indicators for evaluating the performance of a UASB reactor, reflecting its ability to degrade organic matter in wastewater and serving as a key parameter for assessing the efficiency of the anaerobic digestion process.

[0059] The start-up process lasted 35 days, employing a gradual increase in influent COD concentration to stimulate sludge activity. The UASB reactor influent COD concentration was gradually increased from 1000 mg / L to 3000 mg / L over time, in 200 mg / L increments. Initially, the effluent COD concentration of the UASB reactor showed a decreasing trend, primarily because the functional microbial community needed an acclimatization period to adapt to the system environment during anaerobic digestion, gradually restoring its metabolic activity and treatment efficiency. After a period of operation, with an influent COD concentration of 2000 mg / L, the effluent COD concentration of the UASB reactor was approximately 200 mg / L, achieving a removal rate of 90%, representing the highest organic load condition for removal during the entire start-up phase. As the influent COD concentration was gradually increased, the effluent COD concentration of the UASB reactor showed an upward trend. When the influent COD concentration reached 3000 mg / L, the effluent COD concentration of the UASB reactor was around 430 mg / L, with a removal rate of around 85%, and the system gradually stabilized. To prevent system collapse and acidification during subsequent experiments with different feed methods, the subsequent experiments were conducted under the organic loading conditions that best supported the performance of the UASB reactor. This organic loading was 2000 mg / L influent COD and 4 g COD / L / d (d: day).

[0060] Phase 1 Stabilization Preparation: The operation period was 20 days, and the organic load of the UASB reactor was controlled by adjusting the peristaltic pump speed. The influent parameters, i.e., the organic load of the UASB reactor, were 4 g COD / L / d. The COD removal rate of the UASB reactor was maintained at 90 ± 1.5%, and the UASB reactor operated relatively stably.

[0061] Phase Two: Granular Sludge Acclimation Steps: The operation period was 40 days. In this experiment, the influent rate was periodically changed using a peristaltic pump, with each cycle lasting 24 hours. The influent parameters were 8 g COD / L / d (first 12 hours of the cycle) and 0 g COD / L / d (last 12 hours of the cycle). This indicates that the granular sludge cultivation mode in this example was a semi-continuous influent mode (see Figure 4). At the beginning of the granular sludge acclimation step, the reactor COD removal rate decreased from 90.3% to 80.7%, a decrease of 9.6%. As the experiment progressed, the reactor COD removal rate gradually increased. This is because, under certain external pressure, the microorganisms within the reactor underwent adaptive transformation, thus gradually restoring the reactor's performance. (See Figure 5). In this example, the reactor gas production decreased from 7.91 L to 7.07 L. As the reaction continued, the gas production of the UASB reactor in this example gradually recovered. (See Figure 6). In this example, the methane content in the reactor gas decreased from 73.6% to 65.1%, a slight but not drastic decrease. As the experiment progressed, the proportion of methane in the gas produced by the reactor in the example showed a steady upward trend. During this granular sludge acclimation step, the highest proportion of methane in the gas produced by the reactor in the example was 78.5%, indicating that the methane content in the biogas produced by the reactor under the example operating mode was significantly increased.

[0062] Phase 3 Stabilization and Recovery: The operation period was 15 days, with influent parameters of 4 g COD / L / d, and the UASB reactor maintained an organic load of 4 g COD / L / d. Referring to Figure 4, after entering the Phase 3 stable operation phase, the COD removal rate of the UASB reactor continued to increase and eventually stabilized, with the highest removal rate reaching 94.2%. Referring to Figure 5, at the beginning of the stabilization and recovery phase, the UASB reactor experienced a surge in gas production, reaching a maximum of 9.45 L per day. Furthermore, under the experimental conditions, with the overall organic load controlled at the same level, the gas production performance of this example showed a significant improvement after a period of adaptation. The proportion of methane in the gas produced by the UASB reactor showed a significant increase.

[0063] Comparative Example

[0064] Compared to the example, the difference lies in that the influent parameters in stage two of the comparative example are the same as in stage one. That is, in stage two, wastewater with the first COD concentration is continuously fed into the UASB reactor at a fixed flow rate. All other conditions and operating methods are the same as in the example. As a comparative example, the specific operating method is as follows:

[0065] Start-up procedure: Under constant temperature of 37±1℃, the COD:N:P composition of the organic wastewater was set to 200:5:1, and the influent pH was 7-8. While ensuring that the hydraulic load remained unchanged, the COD concentration gradient of the influent was increased during the start-up phase of the UASB reactor to activate the sludge activity. In order to prevent the system from collapsing and acidifying when the feeding method was changed in subsequent experiments, the organic load with the highest treatment efficiency was selected as the organic load for the feeding method experiment to avoid the collapse of the UASB reactor during the feeding method experiment.

[0066] Phase 1 stabilization preparation steps: The operation time is 20 days. The experiment is conducted under the organic load conditions that have the best performance of the UASB reactor. The continuous water influent method is adopted and the influent parameters are 4gCOD / L / d.

[0067] Phase 2 granular sludge acclimatization steps: The operation time is 40 days, and the influent parameters are maintained at 4gCOD / L / d, so that the UASB reactor is operated under the same organic load conditions as in Phase 1.

[0068] Phase 3 stabilization and recovery steps: The operation time is 15 days, the influent parameters are 4gCOD / L / d, and the UASB reactor maintains an organic load of 4gCOD / L / d.

[0069] Comparison results:

[0070] Figure 7 compares the TSS and VSS of the sludge from the UASB reactor in the embodiment of this application with those from the comparative example. TSS and VSS of anaerobic digester sludge are commonly used monitoring indicators in anaerobic digestion, and they are important for assessing the reactor's operating status, treatment efficiency, and microbial activity. In the embodiment, the TSS, VSS, and their ratio in the semi-continuous influent culture mode reactor are all higher than those in the comparative example reactor in the continuous influent mode. The higher VSS / TSS ratio indicates a larger proportion of active microorganisms and biodegradable organic components in the sludge, resulting in higher sludge activity and a stronger ability to metabolize and decompose organic matter. This suggests that the semi-continuous culture mode reactor has a better effect on cultivating activated sludge.

[0071] Figure 8 compares the sludge particle size of the granular sludge cultivation method provided in this embodiment with that of the comparative UASB reactor. The particle size of anaerobic granular sludge plays a crucial role in the UASB anaerobic process, affecting mass transfer efficiency, microbial community structure and activity, and the reactor's processing capacity and efficiency. A suitable granular sludge particle size provides favorable conditions for substrate-microorganism contact. Larger granular sludge particles may exhibit significant stratification, with the outer layer typically consisting of hydrolytic and acid-producing bacteria, while the inner layer primarily contains methanogenic bacteria. This stratified structure allows microorganisms with different functions to collaborate, forming a relatively independent and efficient ecosystem. In the comparative example, the continuous reactor had 42% granular sludge with a particle size greater than 5 mm, 38% granular sludge between 2.5 and 5 mm, and 20% flocculent sludge smaller than 2.5 mm. In the embodiment reactor, the reactor had 60% granular sludge with a particle size greater than 5 mm, 29% granular sludge between 2.5 and 5 mm, and 11% flocculent sludge smaller than 2.5 mm. This indicates that the semi-continuous influent mode is beneficial to the sludge granulation process in the reactor.

[0072] Figure 9 shows the sludge settling velocity of the anaerobic granular sludge cultivation method provided in this embodiment and the sludge settling velocity of the comparative UASB reactor. The anaerobic granular sludge settling velocity is crucial for efficient solid-liquid separation in UASB reactor anaerobic digestion, ensuring sufficient sludge volume, maintaining microbial biomass, and improving mass transfer and reaction efficiency. Monitoring the sludge settling velocity can also assess the performance of the sludge in the reactor and determine whether mineralization or hollowing occurs. The sludge settling velocity of the reactor after continuous cultivation in the comparative embodiment was 62.06 m / h, while the sludge settling velocity of the reactor after semi-continuous cultivation in the embodiment was 84.07 m / h. The sludge settling velocity of the semi-continuous reactor is higher than that of the continuous reactor, consistent with the trend of sludge particle size distribution mentioned above, indicating that the activated sludge particles cultivated in the semi-continuous mode of the embodiment have a good granular structure, high density, and strong microbial activity. Furthermore, the semi-continuous influent mode adopted in this experiment did not cause mineralization or hollowing of granular sludge, which further illustrates that changing the feeding mode helps the granulation process of activated sludge in the anaerobic reactor, and the performance of the activated sludge after cultivation is more advantageous.

[0073] As can be seen from Figures 4 to 6, in Stage 3, the wastewater treatment effect of the activated sludge cultivated in the Example was significantly better than that in the Comparative Example. Referring to Figure 4, at the end of Stage 3, the COD removal rate of the Example remained at approximately 94%, while that of the Comparative Example was approximately 91%. Referring to Figure 5, at the end of Stage 3, the gas production of the Example was approximately 9.45 L, while that of the Comparative Example was approximately 8.33 L. Referring to Figure 6, at the end of Stage 3, the methane content in the gas produced by the Example was approximately 85%, while that of the Comparative Example was approximately 77%.

[0074] After the Phase 3 stabilization and recovery step, the bottom sludge from the UASB reactors of both the example and comparative studies were uniformly measured. In terms of microbial community analysis, the relative abundance of *Bacteroidetes vadinHA17* was 16.12%, *Anaerolineaceae* was 10.52%, and *Aminicenantales* was 9.6% in the initial sludge, making them the dominant bacterial species in the system. However, in reactors cultured under different feed modes, the relative abundance of all three bacteria—*Bacteroidetes vadinHA17*, *Anaerolineaceae*, and *Aminicenantales*—decreased. *Anaerolineaceae* showed the most significant decrease, with its relative abundance falling below 1% in both the example and comparative reactors. Anaerolineaceae, belonging to the genus *Anaerobic*, participates in the decomposition and metabolism of complex organic matter during anaerobic digestion, converting large organic molecules into smaller organic acids and alcohols. This provides more readily available substrates for methanogens, indirectly promoting their growth and methanogenesis. Anaerolineaceae is an acetate-producing fermenting bacterium that exhibits strong synergistic effects with other microorganisms, such as *Methanosaeta*. A decrease in the number or impaired function of symbiotic microorganisms may affect the growth of Anaerolineaceae. The phenomenon observed in this experiment is presumably due to a decrease in the abundance of methanogenic archaea of ​​*Methanosaeta*, leading to a relative decrease in the abundance of Anaerolineaceae. The slight decrease in *Bacteroidetes_vadinHA17* in the reactor of the example reactor is presumably due to changes in the feeding method, potentially resulting in inconsistent substrate supply frequencies and excessively long intervals. *Bacteroidetes_vadinHA17* may have consumed its own stored resources to sustain life during substrate-deficient periods, inhibiting its growth and consequently reducing its relative abundance. The comparative reactor, however, may have experienced a slight decrease in relative abundance due to the proliferation of other, more competitive microorganisms, which put it at a disadvantage in the competition, resulting in fewer resources and limited growth. It is worth noting that the relative abundance distribution of bacteria in the reactor cultured in the example was more even, indicating that no single type of bacteria dominates. The increased species richness and diversity of the entire microbial community facilitates the completion of complex metabolic processes through synergistic interactions among different microorganisms. Furthermore, due to the high diversity and structural stability of the microbial community, when the anaerobic reactor is subjected to external shocks such as a sudden increase in organic load, pH fluctuations, or temperature changes, the rich and relatively balanced bacterial species enable the system to have stronger buffering and adaptability.Different bacteria can adjust their metabolic activities to cope with environmental changes, enabling the system to recover to a stable state more quickly.

[0075] Given the phylogenetic characteristic that methanogens mainly belong to the phylum Euryarchaeota, this application performed species abundance analysis on the sequencing data at the genus level for each sample. The experimental sludge samples mainly contained two genera: *Methanobacterium* and *Methanosaeta*. The relative abundance of *Methanosaeta* in the initial sludge was 29.1%, and that of *Methanobacterium* was 64.3%, indicating that the initial reactor was dominated by hydrogen-trophic methanogens. After experiments with different feeds, the relative abundance of *Methanosaeta* in the comparative reactor was 14.6%, and that of *Methanobacterium* was 76.3%, while in the example reactor, the relative abundance of *Methanosaeta* was 4.4%, and that of *Methanobacterium* was 85.8%. *Methanobacterium* showed growth in both modes, with the most significant growth observed in the example reactor. This indicates that both reactors were transitioning to hydrogen-trophic methanogenesis, with the example reactor showing better results. The growth of *Methanobacterium* in the comparative model demonstrates that even in communities dominated by hydrogenotrophic methanogens, stable continuous culture under low-load conditions can lead to a transformation from acetate-nutritive methanogens to hydrogenotrophic methanogens. Notably, *Methanosarcina* only showed growth in the examples, indicating that this model is conducive to its growth. *Methanosarcina* possesses multiple methanogenic metabolic pathways, enabling it to efficiently produce methane under various substrate conditions. Compared to microorganisms with only a single methanogenic pathway, it can more fully convert substrates into methane, improving the methane yield and efficiency of the anaerobic digestion system. *Methanosarcina* can utilize a variety of complex organic substrates, allowing for more comprehensive substrate degradation and improved system treatment efficiency. Furthermore, *Methanosarcina* exhibits strong biofilm formation capabilities, forming stable biofilm structures on the surface of anaerobic reactor packing or granular sludge, protecting them from external environmental factors. This facilitates microbial interaction and mass transfer, enhancing the stability of the anaerobic digestion system. The highest content of Methanosarcina bacteria was observed after the culturing in the example mode, which may be the reason why its UASB reactor performance was the best as analyzed above.

[0076] The above description is merely a preferred embodiment of this application and is not intended to limit the invention. Various modifications and variations can be made to this invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for cultivating granular sludge, the method utilizing a UASB reactor system, the UASB reactor system comprising a UASB reactor, an inlet pipe, and a peristaltic pump, wherein the UASB reactor has an inlet at its bottom, the inlet being connected to an external wastewater source via the inlet pipe, the peristaltic pump being installed on the inlet pipe for regulating the inlet flow rate, and an outlet at the top of the UASB reactor, the UASB reactor containing anaerobic digested sludge, characterized in that... The anaerobic digestion sludge is activated sludge enriched with hydrotrophic methanogenic bacteria. The method includes the following steps: Start-up step: Wastewater with a second COD concentration is continuously fed into the UASB reactor through the inlet at a fixed flow rate; using the second COD concentration as the initial concentration, the COD concentration of the wastewater flowing into the UASB reactor is gradually increased to 3000 mg / L at intervals of 200 mg / L over time; the COD removal rate of the UASB reactor for wastewater with different COD concentrations is detected; the wastewater COD concentration with the highest COD removal rate by the UASB reactor is determined as the first COD concentration, wherein the first COD concentration is 2000 mg / L and the second COD concentration is 1000 mg / L; Stabilization preparation step: Wastewater with the first COD concentration is continuously fed into the UASB reactor through the inlet at a fixed flow rate, so that the UASB reactor contains anaerobic digestion bacteria. The microbial activity of the oxygen-digested sludge reaches a stable state. In the stabilization preparation step, the organic load of the UASB reactor is a first organic load of 4 g COD / (L·d). In the granular sludge acclimation step, the peristaltic pump is adjusted to change the flow rate of wastewater entering the UASB reactor, so that the UASB reactor operates at a second organic load in the first half of a single acclimation cycle and at zero organic load in the second half of a single acclimation cycle. The second organic load is twice the first organic load. The granular sludge acclimation step consists of multiple acclimation cycles, with each cycle lasting 24 hours, the first half of which is 12 hours, and the second half of which is 12 hours. In the stabilization recovery step, after the granular sludge acclimation step, wastewater with the first COD concentration is continuously fed into the UASB reactor through the inlet at a fixed flow rate, causing the UASB reactor to operate at the first organic load.

2. The method for cultivating granular sludge according to claim 1, characterized in that, The pH value of the wastewater with the first COD concentration flowing into the UASB reactor is 7-8.

3. The method for cultivating granular sludge according to claim 1, characterized in that, The volume of anaerobic digested sludge contained in the UASB reactor is 1 / 2 of the reactor's volume.

4. The method for cultivating granular sludge according to claim 1, characterized in that, The UASB reactor is equipped with a tube body and a sludge hopper. The sludge hopper is located below the tube body, and the inlet is located in the sludge hopper. The tube body includes an inner tube and an outer tube, with an insulation layer between the inner tube and the outer tube. The inner tube contains the main reaction chamber, and the upper part of the UASB reactor is equipped with an exhaust port and an outlet.

5. The method for cultivating granular sludge according to claim 4, characterized in that, The temperature of the insulation layer is 37±1℃.

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