Method for culturing granular sludge

Abstract

The embodiment of the invention provides a method for culturing granular sludge, which comprises the following steps: a stabilization preparation step: continuously feeding sewage with a first COD (Chemical Oxygen Demand) concentration into a UASB (Upflow Anaerobic Sludge Blanket) reactor at a fixed flow speed through a water inlet, so that the activity of microorganisms containing anaerobic digestion sludge in the UASB reactor reaches a stable state, the organic load of the UASB reactor in the stabilization preparation step is a first organic load; the peristaltic pump is adjusted, so that the UASB reactor operates at a second organic load in the first half period of a single domestication period and operates at a zero organic load in the second half period of the single domestication period, the second organic load is two times of the first organic load, the granular sludge domestication step is composed of a plurality of domestication periods, and the second organic load is two times of the first organic load. Compared with a traditional method in the prior art, the method for culturing the granular sludge is higher in efficiency.

Description

Technical Field

[0001] The present application relates to the technical field of sewage treatment, and in particular to a method for cultivating granular sludge. Background Art

[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 global average temperatures to rise by approximately 1.1°C, posing a threat to the human environment. Against this backdrop, reducing greenhouse gas emissions, promoting energy structure transformation, and developing a circular economy have become international consensus. Among these, resource utilization of organic waste is a key path to achieving carbon neutrality. Anaerobic digestion is a biological process that converts organic matter into biogas through microbial metabolism under oxygen-free conditions. This technology combines the dual functions of pollution control and energy recovery, making it a powerful approach to achieving the "dual carbon" goals.

[0003] Traditional anaerobic activated sludge processes suffer from loose structure, poor settling performance, and low sludge concentration in the aeration tank. This limits system efficiency and makes it susceptible 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 long cultivation period for anaerobic granular sludge using activated sludge as inoculum has created numerous challenges for the practical application of granular sludge technology, including increased operating costs and substandard effluent quality during startup. Therefore, accelerating the granulation process of flocculent sludge and achieving large-scale application of anaerobic granular sludge technology has become a major concern in the industry. Summary of the Invention

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

[0006] In a first aspect, an embodiment of the present application provides a method for cultivating granular sludge, the method utilizing a UASB reactor system, the UASB reactor system comprising a UASB reactor, a water inlet pipe, and a peristaltic pump, wherein a water inlet is provided at the bottom of the UASB reactor, the water inlet is connected to an external sewage source through the water inlet pipe, the water inlet pipe is provided with the peristaltic pump for adjusting the water inlet speed, a water outlet is provided at the top of the UASB reactor, and the UASB reactor contains anaerobic digested sludge, characterized in that the method comprises the following steps:

[0007] a stabilization preparation step: continuously flowing sewage having a first COD concentration into the UASB reactor through the water inlet at a fixed flow rate, so that the microbial activity of the anaerobic digested sludge contained 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 acclimation step: adjust the peristaltic pump so that the UASB reactor operates at a second organic load in the first half of a single acclimation cycle and operates at zero organic load in the second half of a single acclimation cycle, wherein the second organic load is twice the first organic load, and the granular sludge acclimation step consists of multiple acclimation cycles.

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

[0010] Startup steps:

[0011] continuously flowing sewage with a second COD concentration into the UASB reactor through the water inlet at a fixed flow rate;

[0012] Taking the second COD concentration as the starting concentration, gradually increasing the COD concentration of the sewage flowing into the UASB reactor over time;

[0013] Detecting the COD removal rate of the UASB reactor for sewage with different COD concentrations;

[0014] The COD concentration of the sewage at which the COD removal rate of the UASB reactor is the highest is determined as the first COD concentration.

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

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

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

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

[0019] In one possible implementation, the UASB reactor is provided with a tube body and a sludge hopper, the sludge hopper is arranged below the tube body, the water inlet is arranged in the sludge hopper, the tube body includes an inner tube and an outer tube, an insulation layer is provided between the inner tube and the outer tube, the inner tube is a main reaction chamber, and an exhaust port and a water outlet are provided at the top of the UASB reactor.

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

[0021] Regarding the method for cultivating granular sludge proposed in the embodiment of the present application, experiments have shown that cultivating anaerobic granular sludge by this method is more efficient than traditional methods. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0023] Figure 1 A schematic structural diagram of a UASB reactor system provided in one embodiment of the present application;

[0024] Figure 2 A schematic diagram of a process for cultivating granular sludge provided in an embodiment of the present application;

[0025] Figure 3 This is a diagram showing the COD concentration changes in the inlet and outlet water of the UASB reactor during the startup step provided in the embodiment of the present application;

[0026] Figure 4 A comparison chart of the COD removal rates of the sewage treatment method based on the UASB reactor provided in the embodiment of the present application and the comparative example;

[0027] Figure 5 A comparison chart of the gas production of the sewage treatment method based on the UASB reactor provided in the embodiment of the present application and the UASB reactor of the comparative example;

[0028] Figure 6 A comparison chart of the methane content in the gas produced by the sewage treatment method based on the UASB reactor provided in the embodiment of the present application and the UASB reactor of the comparative example;

[0029] Figure 7 A comparison chart of TSS and VSS of sludge from a UASB reactor in a comparative example and a method for cultivating granular sludge provided in an embodiment of the present application;

[0030] Figure 8 A comparison chart of sludge particle sizes in the method for cultivating granular sludge provided in the embodiment of the present application and the UASB reactor of the comparative example;

[0031] Figure 9 The sludge settling rate of the method for cultivating granular sludge provided in the embodiment of the present application and the UASB reactor of the comparative example.

[0032] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0033] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of systems and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0034] Currently, the long cultivation period for anaerobic granular sludge using activated sludge as inoculum has brought many problems to the practical application of granular sludge technology, such as increased operating costs and substandard effluent quality during startup. Therefore, how to improve the efficiency of flocculent sludge granulation has become a major concern in the industry.

[0035] See Figure 1 , is a structural diagram of a UASB reactor system provided by an embodiment of the present application, comprising: a UASB reactor 1, a water inlet pipe 2 and a peristaltic pump 3. A water 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 provided below the pipe body 11. Optionally, the sludge hopper is funnel-shaped. The water inlet 121 can be specifically provided at the bottom of the sludge hopper 12. The water inlet 121 is connected to an external sewage source through the water inlet pipe 2. The water pipe 2 is equipped with a peristaltic pump 3 for controlling the inlet flow rate. The main reaction chamber is located within the pipe body 11. The upper portion of the UASB reactor is provided with an exhaust port 13 and a water outlet 14. Furthermore, the pipe body 11 may include an inner tube 111 and an outer tube 112. The inner tube 111 contains the aforementioned main reaction chamber, and an insulation layer 113 is provided between the inner and outer tubes 111 and 112. The upper portion of the UASB reactor is provided with an exhaust port 13 and a water outlet 14. The UASB reactor 1 contains anaerobic digested sludge. In this embodiment of the present application, the peristaltic pump 3 can be used to adjust the inlet flow rate, thereby adjusting the organic load of the UASB reactor within a certain period of time, such as 1 hour or 12 hours.

[0036] See Figure 2 , is a flow chart of a method for cultivating granular sludge provided in an embodiment of the present application, wherein the method utilizes Figure 1 The UASB reactor system shown includes the following steps:

[0037] S201: Startup steps:

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

[0039] For example, see Figure 3 , is a rendering of the COD concentration changes in the inlet and outlet water of the UASB reactor during the startup step provided by the embodiment of the present application. The COD concentration of the UASB reactor inlet water increases from 1000mg / L to 3000mg / L at intervals of 200mg / L. When the inlet COD concentration begins to increase, the COD concentration of the UASB reactor effluent shows a downward trend. This is mainly due to the fact that during the anaerobic digestion process of the UASB reactor, the functional microbial community needs to undergo a certain period of acclimatization to adapt to the system environment, thereby gradually restoring its metabolic activity and treatment efficiency. After running for a period of time, when the inlet COD concentration is 2000mg / L, the UASB reactor effluent COD concentration is about 200mg / L, and the removal rate can reach 90%, which is the organic load condition with the highest removal rate during the entire startup phase. Continuing to gradually increase the inlet COD concentration, it can be seen that the UASB reactor effluent COD concentration shows an upward trend. When the inlet COD concentration reaches 3000mg / L, the UASB reactor effluent COD concentration is about 430mg / L, with a removal rate of about 85%, and the system gradually stabilizes. 2000 mg / L can be set as the first COD concentration. In order to prevent the system from crashing and acidifying when the feed method is changed in the subsequent experiments, the subsequent experiments are carried out under the organic load conditions with the best 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 to directly enter S202.

[0041] S202: Stabilization preparatory steps:

[0042] Sewage with a first COD concentration is continuously fed into the UASB reactor through the water 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. The organic load of the UASB reactor in the 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, it can be considered that the microbial activity of the anaerobic digestion sludge contained in the UASB reactor has reached a stable state. System operation data shows that the anaerobic digestion process has gradually returned to a stable operating state, indicating that the functional microbial community in the UASB reactor has completed adaptive acclimation to the influent COD load, thereby driving the reaction system into a stable operating state and providing a good operating foundation for subsequent process optimization.

[0043] S203: 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 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 step of granulating the flocculent anaerobic digestion sludge.

[0044] Exemplarily, a single cycle is set to 24 hours, and in the first half of the cycle, i.e., the first 12 hours, the sewage enters the UASB reactor at a flow rate four times that in the stable preparation step, and in the second half of the cycle, i.e., the last 12 hours, the sewage is suspended from entering the UASB reactor. The granular sludge acclimation step consists of multiple acclimation cycles, and preferably, the granular sludge acclimation step consists of 40 days.

[0045] Preferably, the anaerobic digestion sludge is activated sludge enriched with hydrogenotrophic methanogens.

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

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

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

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

[0050] The following is an experimental description of the examples and comparative examples of the present application.

[0051] Example

[0052] The system of the present invention (such as Figure 1As shown) 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 embodiment of the present invention.

[0053] The specific implementation method is as follows:

[0054] The sludge inoculated in the laboratory was activated sludge enriched with hydrogenotrophic methanogens. The total suspended solids concentration of the mixed liquor was 24.5 g / L, the volatile suspended solids concentration of the mixed liquor was 15.5 g / L, its VSS / TSS (VSS, VolatileSuspended Solids, volatile suspended solids; TSS, Total Suspended Solids) was 0.63, and the initial settling velocity was 59.4 m / s. The experimental wastewater was artificial 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 artificial synthetic organic wastewater used in the experiment provided in this application.

[0055] Table 1

[0056] Element concentration supplier Peptone 0.80g / L Shenyang Tiexi District Chemical Reagent Factory beef paste 0.50g / L Shenyang Tiexi District Chemical Reagent Factory glucose 0.40g / L Shenyang Tiexi District Chemical Reagent Factory <![CDATA[K2HPO4]]> 0.40g / L Shenyang Tiexi District Chemical Reagent Factory <![CDATA[NH4Cl]]> 0.1g / L Shenyang Tiexi District Chemical Reagent Factory <![CDATA[CaCl2]]> 0.05g / L Shenyang Chemical Co., Ltd. <![CDATA[MgCl2]]> 0.04g / L Shenyang Chemical Co., Ltd. <![CDATA[FeSO4]]> 0.02g / L Shenyang Tiexi District Chemical Reagent Factory zinc sulfate 0.00037mol / L Shenyang Tiexi District Chemical Reagent Factory Manganese sulfate 0.0025mol / L Shenyang Chemical Co., Ltd. copper sulfate 0.00014mol / L Shenyang Chemical Co., Ltd. Cobalt chloride 0.0084mol / L Shenyang Chemical Co., Ltd. Nickel chloride 0.00025mol / L Shenyang Chemical Co., Ltd. Boric acid 0.0008mol / L Shenyang Tiexi District Chemical Reagent Factory EDTA 0.0034 mol / L Liaoning Guangfu Fine Chemical Research Institute

[0057] See Figure 1 Sewage enters through inlet 121 and is discharged from outlet 14 after treatment. Inlet water samples are collected from the sewage source, outlet 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 UASB reactor temperature to maintain 37±1°C.

[0058] The entire study was divided into the UASB reactor startup phase, the first stabilization preparatory phase, the second granular sludge acclimation phase, and the third stabilization recovery phase. COD removal is a core performance indicator for evaluating UASB reactors, reflecting their ability to degrade organic matter in wastewater and a key parameter for assessing the efficiency of the anaerobic digestion process.

[0059] The startup process lasted for 35 days, and the influent COD concentration was gradually increased to stimulate sludge activity. The influent COD concentration of the UASB reactor was increased from 1000 mg / L to 3000 mg / L at intervals of 200 mg / L over time. When the influent COD concentration began to increase, the effluent COD concentration of the UASB reactor showed a downward trend. This was mainly attributed to the fact that during the anaerobic digestion process of the UASB reactor, the functional microbial community needed to undergo 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 effluent COD concentration of the UASB reactor was about 200 mg / L, and the removal rate could reach 90%, which was the organic load condition with the highest removal rate during the entire startup phase. Continue to gradually increase the influent COD concentration, you can see that the UASB reactor effluent COD concentration shows an upward trend. When the influent COD concentration reaches 3000mg / L, the UASB reactor effluent COD concentration is around 430mg / L, the removal rate is around 85%, and the system gradually stabilizes. In order to prevent the system from collapsing and acidifying when the subsequent feed method experiment is carried out, the subsequent experiments are carried out under the organic load conditions with the best performance of the UASB reactor, which is an influent COD concentration of 2000mg / L and an organic load of 4gCOD / L / d (d: day).

[0060] Phase 1: Stabilization Preparatory Steps: The run lasted 20 days. The organic loading of the UASB reactor was controlled by adjusting the peristaltic pump speed. The influent parameters, i.e., the UASB reactor organic loading, were set at 4 gCOD / L / d. The COD removal efficiency of the UASB reactor remained at 90 ± 1.5%, and the UASB reactor operated relatively stably.

[0061] Phase II Granular Sludge Acclimation Step: The operation duration is 40 days. The water inlet adjustment method of this experiment is to periodically change the water inlet rate through peristaltic pump control. Assuming that one cycle is 24 hours, the water inlet parameters are 8gCOD / L / d (in the first 12 hours of the cycle) and 0gCOD / L / d (in the last 12 hours of the cycle). That is, the granular sludge cultivation mode of the embodiment is a semi-continuous water inlet mode. Please refer to Figure 4 At the beginning of the granular sludge acclimation step, the COD removal rate of the reactor dropped from 90.3% to 80.7%, a decrease of 9.6%. As the experiment progressed, the COD removal rate of the reactor gradually increased. This is because under certain external pressure, the microorganisms in the reactor underwent adaptive transformation, which gradually restored the performance of the reactor. Figure 5 , the gas production of the embodiment reactor decreased from 7.91L to 7.07L. As the reaction proceeded, the gas production of the embodiment UASB reactor gradually recovered. Figure 6, the methane content in the gas produced by the embodiment reactor decreased from 73.6% to 65.1%. Although there was a slight decrease, it was not drastic. As the experiment progressed, the methane content in the gas produced by the embodiment reactor showed a steady upward trend. In this granular sludge acclimation step, the methane content in the gas produced by the embodiment reactor reached a maximum of 78.5%, indicating that the methane content of the biogas produced by the reactor in the embodiment operation mode was significantly improved.

[0062] Phase III stabilization recovery step: The operation duration is 15 days, the influent parameter is 4gCOD / L / d, and the UASB reactor maintains an organic load of 4gCOD / L / d. Figure 4 After entering the third stage of stable operation, the COD removal rate of the UASB reactor continued to rise and finally stabilized. The highest removal rate of the UASB reactor was 94.2%. Figure 5 At the start of the stabilization recovery step, the UASB reactor experienced a dramatic increase in gas production, reaching a maximum of 9.45 L per day. Furthermore, under the experimental conditions, maintaining the same overall organic load, the gas production performance of the example was significantly improved after a period of adaptation. The proportion of methane in the gas produced by the UASB reactor increased significantly.

[0063] Comparative Example

[0064] Compared with the embodiment, the difference is that the influent parameters of stage 2 of the comparative example are the same as those of stage 1, that is, in stage 2, the sewage with the first COD concentration is continuously fed into the UASB reactor at a fixed flow rate. The other conditions and operating methods are the same as those of the embodiment. As a comparative example, the specific operating method is as follows:

[0065] Startup steps: Under a constant temperature of 37±1℃, the COD:N:P ratio of the organic sewage components is set to 200:5:1, and the influent pH is 7-8. While ensuring that the hydraulic load remains unchanged, the influent COD concentration gradient is increased during the startup phase of the UASB reactor to stimulate sludge activity. In order to prevent the system from collapsing and acidifying when the subsequent feeding method experiment is carried out, the organic load with the highest treatment efficiency is 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: Preparatory steps for stabilization: The operation duration was 20 days. The organic load condition with the best performance of the UASB reactor was selected for the experiment. Continuous water inflow was adopted, and the inflow parameter was 4 gCOD / L / d.

[0067] Phase II granular sludge acclimation step: The operation duration is 40 days, the influent parameter is maintained at 4 gCOD / L / d, and the UASB reactor is operated under the same organic loading conditions as in Phase I.

[0068] Phase III stabilization recovery step: The operation duration was 15 days, the influent parameter was 4 gCOD / L / d, and the UASB reactor maintained an organic load of 4 gCOD / L / d.

[0069] Comparison results:

[0070] Figure 7 A comparison chart of the method for culturing granular sludge provided in the embodiment of the present application and the TSS and VSS of the UASB reactor sludge in the comparative example. The TSS and VSS of the sludge in the anaerobic digestion reactor are commonly used monitoring indicators in the anaerobic digestion process. They are of great significance for evaluating the operating status, treatment effect and microbial activity of the reactor. The TSS, VSS and the ratio of the two of the sludge in the semi-continuous water inlet culture mode reactor in the embodiment are higher than those in the continuous water inlet mode reactor in the comparative example. Among them, the VSS / TSS ratio is higher, indicating that the active microorganisms and biodegradable organic components in the sludge account for a large proportion, the sludge is more active, and has a stronger ability to metabolize and decompose organic matter, indicating that the reactor after the semi-continuous culture mode has a better effect in culturing activated sludge.

[0071] Figure 8 A comparison chart of the sludge particle size in the anaerobic granular sludge cultivation method provided in the present embodiment and the comparative UASB reactor. The particle size of anaerobic granular sludge is of great significance in the UASB anaerobic process, affecting mass transfer efficiency, microbial community structure and activity, and the reactor's processing capacity and efficiency. An appropriate granular sludge particle size provides favorable conditions for contact between the substrate and microorganisms. Granular sludge with larger particle sizes may exhibit distinct stratification, with the outer layer generally containing hydrolytic and acid-producing bacteria, while the inner layer is primarily composed of methanogens. This layered structure enables microorganisms with different functions to collaborate with each other, forming a relatively independent and efficient ecosystem. In the comparative example, the continuous reactor had granular sludge with a particle size of 5 mm or larger accounting for 42%, granular sludge within 2.5-5 mm accounting for 38%, and the remaining flocculent sludge below 2.5 mm accounting for 20%. In the example reactor, granular sludge with a particle size of 5 mm or larger accounted for 60%, granular sludge within 2.5-5 mm accounting for 29%, and the remaining flocculent sludge below 2.5 mm accounting for 11%. This shows that the semi-continuous water inlet mode is conducive to the sludge granulation process of the reactor.

[0072] Figure 9The method for cultivating granular sludge provided in the embodiment of the present application and the sludge settling rate of the UASB reactor of the comparative example. The settling rate of anaerobic granular sludge has many important significances for anaerobic digestion in the UASB reactor, such as effectively ensuring solid-liquid separation, retaining the amount of sludge in the reactor, maintaining the amount of microorganisms, and improving mass transfer and reaction efficiency. By detecting the sludge settling rate, the performance of the sludge in the reactor can also be evaluated to determine whether the sludge shows trends such as mineralization and hollowing. The sludge settling rate of the reactor after cultivation in the continuous mode of the comparative example is 62.06m / h, and the sludge settling rate of the reactor after cultivation in the semi-continuous mode of the embodiment is 84.07m / h. The sludge settling rate of the semi-continuous reactor is greater than that of the continuous reactor, which is the same as the trend of the sludge particle size ratio above, indicating that the activated sludge particles after cultivation in the semi-continuous mode of the embodiment have good structure, high density, and strong microbial activity. Moreover, the semi-continuous water inlet mode adopted in this experiment did not cause the mineralization and hollowing of granular sludge, which further illustrates that changing the feeding mode method is conducive to the granulation process of activated sludge in the anaerobic reactor, and the performance of the activated sludge after cultivation is more advantageous.

[0073] See also Figures 4 to 6 It can also be seen that in stage 3, the sewage treatment effect of the activated sludge cultured in the embodiment is better than that of the comparative example. Figure 4 At the end of stage 3, the COD removal rate of the embodiment is maintained at about 94%, while that of the comparative example is about 91%. Figure 5 At the end of stage 3, the gas production of the embodiment is about 9.45L, while that of the comparative example is about 8.33L. Figure 6 At the end of the third stage, the methane content in the output gas of the embodiment is about 85%, while that of the comparative example is about 77%.

[0074] After the third stage of stabilization and recovery, the bottom sludge of the UASB reactors of the embodiment and the comparative example was uniformly measured. In terms of microbial community analysis, the relative abundance of Bacteroidetes_vadinHA17 in the initial sludge was 16.12%, the relative abundance of Anaerolineaceae was 10.52%, and the relative abundance of Aminicenantales was 9.6%, which were the more dominant species in the system. In the reactors after cultivation in different feeding modes, the relative abundance of Bacteroidetes_vadinHA17, Anaerolineaceae and Aminicenantales decreased. Among them, the Anaerolineaceae genus performed the most significantly, and the relative abundance of Anaerolineaceae in the embodiment and comparative example reactors was less than 1%. Anaerolineaceae bacteria belong to the genus Anaerolineaceae. During anaerobic digestion, Anaerolineaceae participate in the decomposition and metabolism of complex organic matter, converting large organic molecules into small organic acids and alcohols. This provides methanogens with more readily available substrates, indirectly promoting their growth and methanogenesis. Anaerolineaceae bacteria are acetate-producing fermenters and exhibit strong synergistic interactions with other microorganisms, such as Methanosaeta. When the number of symbiotic microorganisms decreases or their function is impaired, the growth of Anaerolineaceae bacteria may be affected. This phenomenon in this experiment is hypothesized to be due to a decrease in the abundance of Methanosaeta methanogenic archaea, which in turn reduces the relative abundance of Anaerolineaceae bacteria. The slight decrease in the abundance of Bacteroidetes_vadinHA17 in the Example reactor is hypothesized to be due to a change in the feeding method, which may have resulted in an infrequent and prolonged intermittent supply of substrate. During periods of substrate depletion, Bacteroidetes_vadinHA17 may have consumed its own stored substances to sustain life, inhibiting its growth and subsequently reducing its relative abundance. The comparative reactor may be at a disadvantage in the competition due to the large-scale reproduction of other more competitive microorganisms, which results in less resources and limited growth, leading to a slight decrease in relative abundance. It is worth mentioning that the relative abundance of bacteria in the reactor cultured in the embodiment is more evenly distributed, indicating that it is not a single type of bacteria that dominates. The species richness of the entire microbial community is improved and the diversity is increased, which is conducive to the community completing complex metabolic processes through the synergy between different microorganisms. And because the microbial community diversity is high and the structure is stable, when the anaerobic reactor is subjected to external shocks, such as a sudden increase in organic load, pH fluctuations, temperature changes, etc., the rich and relatively balanced bacterial species can make the system have stronger buffering capacity and adaptability.Different bacteria can respond to environmental changes by adjusting their own metabolic activities, allowing the system to return to a stable state more quickly.

[0075] In view of the phylogenetic characteristics that methanogens mainly belong to the Euryarchaeota, this application conducted a species abundance analysis on the sequencing data at the genus level of each sample. There are mainly two genera in the experimental sludge samples, namely Methanobacterium and Methanosaeta. The relative abundance of Methanosaeta in the initial sludge was 29.1%, and the relative abundance of Methanobacterium was 64.3%. It can be seen that the initial reactor is dominated by hydrogenotrophic methanogens. After conducting experiments with different feeds, the relative abundance of Methanosaeta in the comparative reactor was 14.6%, and the relative abundance of Methanobacterium was 76.3%. The relative abundance of Methanosaeta in the example reactor was 4.4%, and the relative abundance of Methanobacterium was 85.8%. Methanobacterium bacteria increased in both modes, and the growth was most significant under the example. This shows that both reactors are converting to hydrogenotrophic methanogenesis, and the example has better results. The growth of Methanobacterium in the comparative model shows that a community dominated by hydrogenotrophic methanogens will also experience a transformation from acetotrophic methanogens to hydrogenotrophic methanogens when cultured stably and continuously under low load conditions. It is worth mentioning that Methanosarcina bacteria only grew in the examples, indicating that this model is conducive to the growth of this bacterium. Methanosarcina bacteria have multiple methane-producing metabolic pathways, and these diverse metabolic pathways enable them to efficiently produce methane under different substrate conditions. Compared with microorganisms with only a single methane-producing pathway, they can more fully convert substrates into methane, thereby improving the methane production and production efficiency of the anaerobic digestion system. Methanosarcina bacteria can grow on a variety of complex organic substrates, which enables them to degrade substrates more comprehensively and improve the treatment effect of the system. Methanosarcina bacteria also have a strong biofilm-forming ability and can form a stable biofilm structure on the surface of the filler or granular sludge of the anaerobic reactor to protect it from the influence of external environmental factors, facilitate the interaction and material transfer between microorganisms, and enhance the stability of the anaerobic digestion system. The content of Methanosarcina bacteria was the highest after culture in the embodiment model, which may be the reason why the performance of its UASB reactor was the best as analyzed above.

[0076] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for cultivating granular sludge, the method utilizing a UASB reactor system, the UASB reactor system comprising a UASB reactor, a water inlet pipe, and a peristaltic pump, wherein a water inlet is provided at the bottom of the UASB reactor, the water inlet being connected to an external sewage source via the water inlet pipe, the peristaltic pump being provided on the water inlet pipe for adjusting the water inlet speed, a water outlet being provided at the top of the UASB reactor, and the UASB reactor containing anaerobic digested sludge, characterized in that: The method comprises the following steps: a stabilization preparation step: continuously flowing sewage having a first COD concentration into the UASB reactor through the water inlet at a fixed flow rate, so that the microbial activity of the anaerobic digested sludge contained 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; Granular sludge acclimation step: adjust the peristaltic pump so that the UASB reactor operates at a second organic load in the first half of a single acclimation cycle and operates at zero organic load in the second half of a single acclimation cycle, wherein the second organic load is twice the first organic load, and the granular sludge acclimation step consists of multiple acclimation cycles.

2. The method for cultivating granular sludge according to claim 1, characterized in that: Before the stable operation step, the method further includes: Startup steps: continuously flowing sewage with a second COD concentration into the UASB reactor through the water inlet at a fixed flow rate; Taking the second COD concentration as the starting concentration, gradually increasing the COD concentration of the sewage flowing into the UASB reactor over time; Detecting the COD removal rate of the UASB reactor for sewage with different COD concentrations; The COD concentration of the sewage at which the COD removal rate of the UASB reactor is the highest is determined as the first COD concentration.

3. The method for cultivating granular sludge according to claim 1, characterized in that: The anaerobic digestion sludge is activated sludge enriched with hydrogenotrophic methanogens.

4. The method for cultivating granular sludge according to claim 1, characterized in that: The first COD concentration is 2000 mg / L.

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

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

7. The method for cultivating granular sludge according to claim 1, characterized in that: The UASB reactor is provided with a tube body and a sludge hopper, the sludge hopper is arranged below the tube body, the water inlet is arranged in the sludge hopper, the tube body includes an inner tube and an outer tube, an insulation layer is provided between the inner tube and the outer tube, the inner tube is a main reaction chamber, and an exhaust port and a water outlet are provided at the top of the UASB reactor.

8. The method for cultivating granular sludge according to claim 1, characterized in that: The temperature of the insulation layer is 37±1°C.

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