Anaerobic fermentation accelerant as well as preparation method and application thereof

Abstract

The invention provides an anaerobic fermentation accelerant as well as a preparation method and application thereof, and relates to the field of anaerobic fermentation. The preparation method comprises the following steps: synthesizing a magnetic carbon quantum dot compound; dispersing the magnetic carbon quantum dot compound in an MES buffer solution, carrying out ultrasonic treatment for 30-40 minutes, then adding N-(3-dimethylaminopropyl)-N '-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide, and stirring for 30-40 minutes under the conditions of room temperature and light shielding, so as to obtain an activated turbid liquid; dispersing methoxyl-polyethylene glycol-amine in an MES buffer solution, then dropwise adding the MES buffer solution into the activated turbid liquid, and stirring to react for 12-24 hours; and S6, performing centrifugation, magnetic separation, washing and drying on the product in the step S5 to obtain the accelerant. The accelerant point has magnetism, and the surface of the accelerant point is grafted with a hydrophilic polymer, so that a hydration layer is formed, steric hindrance is formed, macromolecules are prevented from approaching and being adsorbed on the surface of the carbon quantum dot, and the activity of the carbon quantum dot is prolonged.

Description

Technical Field

[0001] This invention relates to the field of anaerobic fermentation, and more specifically, to an anaerobic fermentation promoter, its preparation method, and its application. Background Technology

[0002] Anaerobic fermentation is a biochemical process that decomposes organic matter through the metabolic action of microbial communities under anaerobic conditions. It is widely used in waste treatment, energy production, and agricultural recycling systems, and is also one of the key pathways for the resource utilization of organic waste.

[0003] Anaerobic fermentation involves three key stages. Hydrolysis stage Complex organic matter (such as cellulose and protein) is broken down into simple sugars, amino acids, etc. Acid production stage The hydrolysis products are further converted into acetic acid, hydrogen, and carbon dioxide. methanogenesis stage Methanogens convert acetic acid, hydrogen, and other gases into methane (CH4) and carbon dioxide. Organic matter and microorganisms are the main raw materials for anaerobic fermentation. In the three stages mentioned above, microorganisms play a crucial role, and the conversion rate of the final product depends on the biological activity of the microorganisms, their growth rate, and the efficiency of electron transfer between them.

[0004] To improve the activity of microbial bacteria, patent CN 117247978 A discloses a method for extending the anaerobic fermentation chain to produce hexanoic acid. A doped carbon quantum dot promoter is dispersed in deionized water and then added to a serum bottle containing culture medium and inoculum for anaerobic fermentation chain extension to produce hexanoic acid. Using doped carbon quantum dots as a promoter effectively solves the problems of low hexanoic acid yield and long reaction lag period in the anaerobic fermentation chain extension process. Patent CN 107604011 A discloses a method for improving anaerobic fermentation gas production using carbon quantum dots as a promoter. Solid carbon quantum dots are added to the inoculum, mixed evenly, and then anaerobic fermentation raw materials are added to the resulting mixture for anaerobic fermentation. The addition of carbon quantum dot promoters can improve the synergistic effect among fermenting microbial communities, thereby significantly increasing the methane production rate and total gas production. Patent CN103255179A discloses a biogas fermentation promoter and its preparation method. The fermentation promoter is composed of trace metal elements such as Fe, Co, Ni, and Zn, which can increase the system's gas production and the methane content in biogas. At the same time, the removal rates of COD, TS, and VS are also significantly improved.

[0005] Adding carbon quantum dots (CQDs) to fermentation feedstock can enhance the synergistic effect between microorganisms. However, during fermentation, macromolecules such as proteins and polysaccharides in the fermentation system may adsorb onto the surface of CQDs, covering their active sites and gradually losing their electronic mediating function. Secondly, due to the small size of carbon quantum dots, they are difficult to recover. After fermentation, it is almost impossible to effectively separate them from fermentation residues (biogas residue and biogas slurry) through conventional sedimentation and filtration methods. The residual carbon quantum dots may have adverse effects on soil microbial communities, plant growth, and other longevity factors. Summary of the Invention

[0006] The purpose of this invention is to provide an anaerobic fermentation promoter that combines carbon quantum dots with magnetic iron oxide, which can effectively recover carbon quantum dots from fermentation residue.

[0007] Another objective of this invention is to provide a method for preparing an anaerobic fermentation promoter. The promoter prepared by this method has magnetic carbon quantum dots with hydrophilic polymers grafted onto their surface to form a hydration layer. This creates steric hindrance, preventing macromolecules from approaching and adsorbing onto the surface of the carbon quantum dots, thereby prolonging the activity of the carbon quantum dots.

[0008] The third objective of this invention is to provide an anaerobic fermentation promoter for the anaerobic fermentation of coffee grounds to produce methane, which can improve the fermentation efficiency of coffee grounds.

[0009] The technical problem solved by this invention is achieved by the following technical solution.

[0010] On one hand, embodiments of the present invention provide an anaerobic fermentation promoter, comprising the following steps: S1, dissolve carbon source, nitrogen source and iron source in water, and disperse by ultrasonication to obtain precursor solution; S2, the precursor solution is added to a high-pressure reactor and reacted at 160-200℃ for 8-10 hours, then cooled to room temperature. Under high temperature and high pressure, the carbon and nitrogen sources polymerize and carbonize to form nitrogen-doped carbon quantum dots; simultaneously, iron ions are reduced and nucleated to crystallize, generating Fe3O4 nanoparticles. The two are bonded through surface functional groups (-COOH, -OH) to ultimately form a magnetic carbon quantum dot composite.

[0011] S3. The product in the high-pressure reactor is magnetically separated, washed, dried and ground to obtain a magnetic carbon quantum dot composite. S4, the magnetic carbon quantum dot complex is dispersed in MES buffer, sonicated for 30-40 min, and then N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide are added. The mixture is stirred for 30-40 min at room temperature and in the dark to obtain an activated suspension. S5, methoxy-polyethylene glycol-amine is dispersed in MES buffer, and then added dropwise to the activated suspension. The mixture is stirred and reacted at room temperature and in the dark for 12-24 hours. S6. The product from step S5 is centrifuged, magnetically separated, washed, and dried to obtain the promoter.

[0012] In some embodiments of the present invention, the carbon source is at least one selected from citric acid, glucose, and ascorbic acid. More preferably, citric acid is used as the carbon source.

[0013] In some embodiments of the present invention, the nitrogen source is at least one selected from urea, ethylenediamine, and triethanolamine. Preferably, urea is used as the nitrogen source.

[0014] In some embodiments of the present invention, the iron source is ferric chloride or ferric ammonium citrate. More preferably, ferric chloride is used as the iron source.

[0015] In some embodiments of the present invention, the molar ratio of carbon source, nitrogen source and iron source in the precursor solution is 2:(1-3):(0.1-0.5).

[0016] In some embodiments of the present invention, the molar ratio of carbon source, nitrogen source and iron source in the precursor solution is 2:2:0.25.

[0017] In some embodiments of the present invention, in step S5, the mass ratio of methoxy-polyethylene glycol-amine to the magnetic carbon quantum dot complex in the activated suspension is (4-5):1. More preferably, the mass ratio is 5:1.

[0018] In some embodiments of the present invention, in steps S4 and S5, the stirring speed is 100-200 rpm.

[0019] An anaerobic fermentation promoter is used in the anaerobic fermentation of coffee grounds to produce methane. The fermentation substrate, by weight, includes the following raw materials: 30-40 parts coffee grounds, 10-20 parts soybean meal, 5-10 parts poultry manure, 10-15 parts corn stalks, 0.5-1 parts methanogenic bacteria, and 0.1-0.5 parts promoter.

[0020] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: The anaerobic fermentation promoter provided by this invention synthesizes magnetic carbon quantum dots through a one-step hydration process, and then hydrophilically modifies the surface of the magnetic carbon quantum dots by grafting polyethylene glycol molecular chains. When this promoter is applied to an anaerobic fermentation system, the carbon quantum dots can improve the electron transfer efficiency between microorganisms, and the hydrophilic groups on the surface of the carbon quantum dots can provide greater steric hindrance and a hydrophilic layer, reducing the loading of protein and polysaccharide macromolecules in the fermentation system, prolonging the activity of the carbon quantum dots, and increasing the gas production of the fermentation system.

[0021] Applying this promoter to the fermentation of coffee grounds can effectively improve the fermentation efficiency and increase methane production. At the same time, the recyclable promoter does not affect the further application of the subsequent fermentation system. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to specific embodiments.

[0024] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0025] Example 1 The anaerobic fermentation promoter of this embodiment was prepared according to the following method: S1, (20 mmol) citric acid, (20 mmol) urea and (0.5 mmol) ferric chloride hexahydrate were dissolved in 100 mL of water and ultrasonically dispersed for 30 min to obtain the precursor solution; S2, the precursor solution is added to a high-pressure reactor lined with polytetrafluoroethylene, sealed, and then placed in a forced-air drying oven. The reactor is heated to 180°C and reacted for 8 hours, and then cooled to room temperature naturally. S3. Open the reactor and bring a neodymium iron boron strong magnet close to the container wall. The composite material is quickly attracted to the magnet. Pour off the supernatant and add an appropriate amount of anhydrous ethanol and deionized water (volume ratio 1:1). After ultrasonic dispersion, perform magnetic separation again. Repeat this process 4 times to completely remove unreacted ions and byproducts. Transfer the washed wet gel-like product to a petri dish and place it in a vacuum drying oven. Dry it at 60 °C for 12 h. Gently grind the dried block product in an agate mortar to obtain a uniform black powder, which is the magnetic carbon quantum dot composite. S4. 100 mg of magnetic carbon quantum dot complex was dispersed in 50 mL of 0.1 M MES buffer (pH=5.5), sonicated for 30 min, and then 100 mg of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and 60 mg of N-hydroxysuccinimide were added. The mixture was placed on a shaker and stirred at 150 rpm for 30 min at room temperature and in the dark to activate the carboxyl groups to form active esters, thus obtaining an activated suspension. S5, 500 mg of methoxy-polyethylene glycol-amine was dispersed in 5 mL of 0.1 M MES buffer, and then added dropwise to the activated suspension. The reaction was continued on a shaker at room temperature and in the dark for 24 h at a speed of 150 rpm to complete the amidation reaction. After step S6 is completed, the reaction solution is transferred to a centrifuge tube and magnetically separated using a strong magnet. The supernatant is discarded, and the solution is redispersed and magnetically separated again with ultrapure water. This washing process is repeated 5-6 times to thoroughly remove unreacted PEG, urea byproducts, and excess EDC and NHS. The washed solid is dispersed in a small amount of water and freeze-dried (-20℃, 24h) to obtain a fluffy black powder, which is the accelerator.

[0026] Example 2 The anaerobic fermentation promoter of this embodiment was prepared according to the following method: S1, (20 mmol) citric acid, (20 mmol) urea and (0.25 mmol) ferric chloride hexahydrate were dissolved in 100 mL of water and ultrasonically dispersed for 30 min to obtain the precursor solution; S2, the precursor solution is added to a high-pressure reactor lined with polytetrafluoroethylene, sealed, and then placed in a forced-air drying oven. The reactor is heated to 160°C and reacted for 10 hours, and then cooled to room temperature naturally. S3. Open the reactor and bring a neodymium iron boron strong magnet close to the container wall. The composite material is quickly attracted to the magnet. Pour off the supernatant and add an appropriate amount of anhydrous ethanol and deionized water (volume ratio 1:1). After ultrasonic dispersion, perform magnetic separation again. Repeat this process 4 times to completely remove unreacted ions and byproducts. Transfer the washed wet gel-like product to a petri dish and place it in a vacuum drying oven. Dry it at 60 °C for 12 h. Gently grind the dried block product in an agate mortar to obtain a uniform black powder, which is the magnetic carbon quantum dot composite. S4. 100 mg of magnetic carbon quantum dot complex was dispersed in 50 mL of 0.1 M MES buffer (pH=5.5), sonicated for 30 min, and then 100 mg of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and 60 mg of N-hydroxysuccinimide were added. The mixture was placed on a shaker and stirred at 150 rpm for 30 min at room temperature and in the dark to activate the carboxyl groups to form active esters, thus obtaining an activated suspension. S5, 400 mg of methoxy-polyethylene glycol-amine was dispersed in 5 mL of 0.1 M MES buffer, and then added dropwise to the activated suspension. The reaction was continued on a shaker at room temperature and in the dark for 24 h at a speed of 150 rpm to complete the amidation reaction. After step S6 is completed, the reaction solution is transferred to a centrifuge tube and magnetically separated using a strong magnet. The supernatant is discarded, and the solution is redispersed and magnetically separated again with ultrapure water. This washing process is repeated 5-6 times to thoroughly remove unreacted PEG, urea byproducts, and excess EDC and NHS. The washed solid is dispersed in a small amount of water and freeze-dried (-20℃, 24h) to obtain a fluffy black powder, which is the accelerator.

[0027] Example 3 The anaerobic fermentation promoter of this embodiment was prepared according to the following method: S1, (20 mmol) citric acid, (30 mmol) triethanolamine and (0.5 mmol) ferric ammonium citrate were dissolved in 100 mL of water and ultrasonically dispersed for 30 min to obtain the precursor solution; S2, the precursor solution is added to a high-pressure reactor lined with polytetrafluoroethylene, sealed, and then placed in a forced-air drying oven. The reactor is heated to 200°C and reacted for 8 hours, and then cooled to room temperature naturally. S3. Open the reactor and bring a neodymium iron boron strong magnet close to the container wall. The composite material is quickly attracted to the magnet. Pour off the supernatant and add an appropriate amount of anhydrous ethanol and deionized water (volume ratio 1:1). After ultrasonic dispersion, perform magnetic separation again. Repeat this process 4 times to completely remove unreacted ions and byproducts. Transfer the washed wet gel-like product to a petri dish and place it in a vacuum drying oven. Dry it at 60 °C for 12 h. Gently grind the dried block product in an agate mortar to obtain a uniform black powder, which is the magnetic carbon quantum dot composite. S4. 100 mg of magnetic carbon quantum dot complex was dispersed in 50 mL of 0.1 M MES buffer (pH=5.5), sonicated for 30 min, and then 100 mg of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and 60 mg of N-hydroxysuccinimide were added. The mixture was placed on a shaker and stirred at 150 rpm for 30 min at room temperature and in the dark to activate the carboxyl groups to form active esters, thus obtaining an activated suspension. S5, 450 mg of methoxy-polyethylene glycol-amine was dispersed in 5 mL of 0.1 M MES buffer, and then added dropwise to the activated suspension. The reaction was continued on a shaker at room temperature and in the dark for 24 h at a speed of 150 rpm to complete the amidation reaction. After step S6 is completed, the reaction solution is transferred to a centrifuge tube and magnetically separated using a strong magnet. The supernatant is discarded, and the solution is redispersed and magnetically separated again with ultrapure water. This washing process is repeated 5-6 times to thoroughly remove unreacted PEG, urea byproducts, and excess EDC and NHS. The washed solid is dispersed in a small amount of water and freeze-dried (-20℃, 24h) to obtain a fluffy black powder, which is the accelerator.

[0028] Example 4 The anaerobic fermentation promoter of this embodiment was prepared according to the following method: S1, dissolve (20 mmol) ascorbic acid, (10 mmol) ethylenediamine and (0.5 mmol) ferric ammonium citrate in 100 mL of water and sonicate for 30 min to obtain the precursor solution; S2, the precursor solution is added to a high-pressure reactor lined with polytetrafluoroethylene, sealed, and then placed in a forced-air drying oven. The reactor is heated to 160°C and reacted for 10 hours, and then cooled to room temperature naturally. S3. Open the reactor and bring a neodymium iron boron strong magnet close to the container wall. The composite material is quickly attracted to the magnet. Pour off the supernatant and add an appropriate amount of anhydrous ethanol and deionized water (volume ratio 1:1). After ultrasonic dispersion, perform magnetic separation again. Repeat this process 4 times to completely remove unreacted ions and byproducts. Transfer the washed wet gel-like product to a petri dish and place it in a vacuum drying oven. Dry it at 60 °C for 12 h. Gently grind the dried block product in an agate mortar to obtain a uniform black powder, which is the magnetic carbon quantum dot composite. S4. 100 mg of magnetic carbon quantum dot complex was dispersed in 50 mL of 0.1 M MES buffer (pH=5.5), sonicated for 30 min, and then 100 mg of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and 60 mg of N-hydroxysuccinimide were added. The mixture was placed on a shaker and stirred at 150 rpm for 30 min at room temperature and in the dark to activate the carboxyl groups to form active esters, thus obtaining an activated suspension. S5, 500 mg of methoxy-polyethylene glycol-amine was dispersed in 5 mL of 0.1 M MES buffer, and then added dropwise to the activated suspension. The reaction was continued on a shaker at room temperature and in the dark for 24 h at a speed of 150 rpm to complete the amidation reaction. After step S6 is completed, the reaction solution is transferred to a centrifuge tube and magnetically separated using a strong magnet. The supernatant is discarded, and the solution is redispersed and magnetically separated again with ultrapure water. This washing process is repeated 5-6 times to thoroughly remove unreacted PEG, urea byproducts, and excess EDC and NHS. The washed solid is dispersed in a small amount of water and freeze-dried (-20℃, 24h) to obtain a fluffy black powder, which is the accelerator.

[0029] Example 5 The anaerobic fermentation promoter of this embodiment was prepared according to the following method: S1, Dissolve (20 mmol) glucose, (10 mmol) triethanolamine and (0.5 mmol) ferric ammonium citrate in 100 mL of water and sonicate for 30 min to obtain a precursor solution; S2, the precursor solution is added to a high-pressure reactor lined with polytetrafluoroethylene, sealed, and then placed in a forced-air drying oven. The reactor is heated to 180°C and reacted for 8 hours, and then cooled to room temperature naturally. S3. Open the reactor and bring a neodymium iron boron strong magnet close to the container wall. The composite material is quickly attracted to the magnet. Pour off the supernatant and add an appropriate amount of anhydrous ethanol and deionized water (volume ratio 1:1). After ultrasonic dispersion, perform magnetic separation again. Repeat this process 4 times to completely remove unreacted ions and byproducts. Transfer the washed wet gel-like product to a petri dish and place it in a vacuum drying oven. Dry it at 60 °C for 12 h. Gently grind the dried block product in an agate mortar to obtain a uniform black powder, which is the magnetic carbon quantum dot composite. S4. 100 mg of magnetic carbon quantum dot complex was dispersed in 50 mL of 0.1 M MES buffer (pH=5.5), sonicated for 30 min, and then 100 mg of N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and 60 mg of N-hydroxysuccinimide were added. The mixture was placed on a shaker and stirred at 150 rpm for 30 min at room temperature and in the dark to activate the carboxyl groups to form active esters, thus obtaining an activated suspension. S5, 500 mg of methoxy-polyethylene glycol-amine was dispersed in 5 mL of 0.1 M MES buffer, and then added dropwise to the activated suspension. The reaction was continued on a shaker at room temperature and in the dark for 24 h at a speed of 150 rpm to complete the amidation reaction. After step S6 is completed, the reaction solution is transferred to a centrifuge tube and magnetically separated using a strong magnet. The supernatant is discarded, and the solution is redispersed and magnetically separated again with ultrapure water. This washing process is repeated 5-6 times to thoroughly remove unreacted PEG, urea byproducts, and excess EDC and NHS. The washed solid is dispersed in a small amount of water and freeze-dried (-20℃, 24h) to obtain a fluffy black powder, which is the accelerator.

[0030] Experimental Example In a 1L fermentation flask, according to the proportions in Table 1, 200g of fermentation substrate and a small amount of water were added, controlling the moisture content to 60%. Anaerobic fermentation was carried out at a mesophilic temperature (35℃) for 28 days. The gas production was measured, and the results are shown in Table 2. Each group underwent three parallel experiments, and the average value was taken. The methanobacterium was BioBio Biotechnology, DSM 1053.

[0031] Table 1 The accelerators added in groups 1-5 correspond to the accelerators in Examples 1-5, respectively. The accelerator added in the control group is the magnetic carbon quantum dot composite prepared in Example 1, and no accelerator was added in the control group.

[0032] Table 2 Table 2 shows that adding the promoters from Examples 1-5 to the fermentation system resulted in 2 / 3 of the total gas production in the first 15 days, indicating that the addition of the promoters accelerated fermentation, shortened fermentation time, and increased total gas production. In the control group, where the promoters were not hydrophilically modified, the gas production decreased compared to Examples 1-5 in the later stages of fermentation, suggesting that the promoters may have become inactive during fermentation, leading to reduced electron transfer efficiency between microorganisms and consequently decreased gas production.

[0033] After fermentation, magnets were brought close to each fermentation tank for magnetic adsorption, and then the promoter was separated and recovered. The promoter recovery rate of each fermentation tank is shown in Table 3.

[0034] Table 3 As shown in Table 2, the recovery rate of magnetic promoters from fermentation broth can reach over 80%, reducing the residual carbon quantum dots in the fermentation broth and allowing for reuse.

[0035] In summary, the anaerobic fermentation promoter provided in this invention involves the one-step hydration process to synthesize magnetic carbon quantum dots, followed by hydrophilic modification of the surface of the magnetic carbon quantum dots and grafting of polyethylene glycol molecular chains. When applied to an anaerobic fermentation system, the carbon quantum dots improve the electron transfer efficiency between microorganisms. Furthermore, the hydrophilic groups on the surface of the carbon quantum dots provide significant steric hindrance and a hydrophilic layer, reducing the loading of protein and polysaccharide macromolecules in the fermentation system, prolonging the activity of the carbon quantum dots, and increasing the gas production of the fermentation system.

[0036] The embodiments described above are some, but not all, embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing an anaerobic fermentation promoter, characterized in that, Includes the following steps: S1, dissolve carbon source, nitrogen source and iron source in water, and disperse by ultrasonication to obtain precursor solution; S2, the precursor solution is added to a high-pressure reactor and reacted at 160-200℃ for 8-10 hours, then cooled to room temperature; S3. The product in the high-pressure reactor is magnetically separated, washed, dried and ground to obtain a magnetic carbon quantum dot composite. S4, the magnetic carbon quantum dot complex is dispersed in MES buffer, sonicated for 30-40 min, and then N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide are added. The mixture is stirred for 30-40 min at room temperature and in the dark to obtain an activated suspension. S5, methoxy-polyethylene glycol-amine is dispersed in MES buffer, and then added dropwise to the activated suspension. The mixture is stirred and reacted at room temperature and in the dark for 12-24 hours. S6. The product from step S5 is centrifuged, magnetically separated, washed, and dried to obtain the promoter.

2. The method for preparing the anaerobic fermentation promoter according to claim 1, characterized in that, The carbon source is at least one of citric acid, glucose, and ascorbic acid.

3. The method for preparing the anaerobic fermentation promoter according to claim 1, characterized in that, The nitrogen source is at least one of urea, ethylenediamine, and triethanolamine.

4. The method for preparing the anaerobic fermentation promoter according to claim 1, characterized in that, The iron source is ferric chloride or ferric ammonium citrate.

5. The method for preparing the anaerobic fermentation promoter according to claim 1, characterized in that, In the precursor solution, the molar ratio of carbon source, nitrogen source and iron source is 2:(1-3):(0.1-0.5).

6. The method for preparing the anaerobic fermentation promoter according to claim 1, characterized in that, In the precursor solution, the molar ratio of carbon source, nitrogen source and iron source is 2:2:0.

25.

7. The method for preparing the anaerobic fermentation promoter according to claim 1, characterized in that, In step S5, the mass ratio of methoxy-polyethylene glycol-amine to the magnetic carbon quantum dot complex in the activated suspension is (4-5):

1.

8. The method for preparing the anaerobic fermentation promoter according to claim 1, characterized in that, In steps S4 and S5, the stirring speed is 100-200 rpm.

9. An anaerobic fermentation promoter, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of an anaerobic fermentation promoter in the anaerobic fermentation of coffee grounds to produce methane, characterized in that, The fermented base material, by weight, includes the following ingredients: The ingredients are: 30-40 parts coffee grounds, 10-20 parts soybean meal, 5-10 parts poultry manure, 10-15 parts corn stalks, 0.5-1 part methanogenic bacteria agent, and 0.1-0.5 parts accelerator prepared by the method described in any one of claims 1-8.

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