Amorphous iron-manganese-oxygen cluster, preparation method thereof and application of amorphous iron-manganese-oxygen cluster in enhancing methanogenesis of functional enzyme

Abstract

The invention provides an amorphous ferrum-manganese-oxygen cluster, a preparation method thereof and application of the amorphous ferrum-manganese-oxygen cluster in enhancing methanogenesis of functional enzyme, and belongs to the cross technical field of environmental functional materials and waste biological treatment and recycling. The method comprises the following steps: mixing manganese salt with a hydrochloric acid solution to obtain a hydrochloric acid solution of the manganese salt; dissolving ferric salt in water to obtain a ferric salt solution; a hydrochloric acid solution of manganese salt and a ferric salt solution are mixed and then heated, then an isopropanolamine solution is added for a reaction, and the amorphous iron-manganese oxygen cluster is obtained. The dispersion liquid of the amorphous ferro-manganese oxygen cluster is added into mixed bacteria granular sludge to be sequentially subjected to activating treatment and anaerobic digestion, and can be used as an enhancer and a protective agent of anaerobic microorganism functional enzyme, and the influence of intermediate acid on the methane production process is eliminated by means of chelation or adsorption and the like; the yield of adenosine triphosphate of methanogenic archaea can be increased, the growth of archaea is accelerated, and the growth difference between archaea and acidogen bacteria is balanced.

Description

Technical Field

[0001] The invention relates to the cross-technical field of environmental functional materials, waste biological treatment and resource utilization, and in particular to an amorphous iron-manganese-oxygen cluster and a preparation method thereof and the application of enhanced functional enzymes in producing methane. Background Art

[0002] Anaerobic biological treatment technology is a process in which facultative anaerobic and anaerobic microbial communities convert organic matter into methane and carbon dioxide under anaerobic conditions, also known as anaerobic digestion. With the development of wastewater anaerobic biological technology, the removal of organic matter in wastewater can basically meet the requirements of effluent water quality. As the main body of anaerobic biological treatment, anaerobic sludge, its efficient biological methane production performance is not only a guarantee for the efficient operation of anaerobic biological treatment processes, but may also provide a new way for future energy development. However, the current anaerobic biological treatment technology has the following bottleneck problems in the treatment of waste and resource utilization:

[0003] (1) Substrate-induced inhibition: Various inhibitory substances and intermediate products are one of the rate-limiting factors. During the anaerobic digestion process, substrate-induced inhibition will affect anaerobic stability, such as high concentrations of free ammonia, volatile fatty acids (VFAs) and sulfide / sulfate. These acidic substances will inhibit microbial activity, causing the anaerobic digestion system to become unstable or even collapse;

[0004] (2) Poor process stability: Acidogens (belonging to bacteria) and methanogens (belonging to archaea) are physiologically different, and their growth rates and sensitivities to anaerobic digestion process operating conditions are also different. Changes in environmental factors (including temperature, pH value, H2 partial pressure and organic loading rate) will affect the population balance and functional coordination of the two, leading to imbalance in the anaerobic digestion process and decreased efficiency;

[0005] (3) Electron transfer limitation: Mediated interspecies electron transfer (MIET) is an important mechanism of traditional anaerobic digestion. MIET is the process of transferring electrons from one microorganism to another using H2 or formate (HCOOH) as electron carriers. H2 and HCOOH are usually transferred by diffusion in anaerobic environments. However, the diffusion-based MIET transfer rate is very slow, and compounds are easy to escape during mass transfer, which can easily cause electron loss; in addition, MIET is also susceptible to interference from environmental factors, such as the above-mentioned substrate-induced inhibition that causes MIET interruption. On the other hand, direct electron transfer (DIET) pathways can be formed by using the conductive cilia and membrane-bound electron transport proteins of microorganisms, but there are also problems of electron transfer interruption and low substrate utilization efficiency.

[0006] The search shows that the electron transfer pathway enhanced by conductive materials is a potential method to solve the above technical bottlenecks. Therefore, based on the structure and characteristics of the functional enzyme of anaerobic methanogens, the present invention proposes to provide an amorphous iron-manganese-oxygen cluster and its preparation method through enzyme-mimicking process and directional design, and apply it to the process of enhancing microbial anaerobic methanogenesis, breaking through the limitations of the electron transfer process of anaerobic methanogenesis. Summary of the invention

[0007] The purpose of the present invention is to provide an amorphous iron-manganese oxygen cluster and a preparation method thereof and an application of enhanced functional enzyme methanogenesis to solve the problems of substrate-induced inhibition, poor process stability and limited electron transfer in existing anaerobic biological treatment methanogenesis technology.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0009] The present invention provides a method for preparing an amorphous iron-manganese-oxygen cluster, comprising the following steps:

[0010] (1) mixing a manganese salt and a hydrochloric acid solution to obtain a hydrochloric acid solution of a manganese salt;

[0011] (2) dissolving iron salt in water to obtain an iron salt solution;

[0012] (3) A hydrochloric acid solution of a manganese salt and an iron salt solution are mixed and heated, and then an isopropanolamine solution is added to react to obtain an amorphous iron-manganese oxide cluster.

[0013] Preferably, in step (1), the molar volume ratio of the manganese salt to the hydrochloric acid solution is 5-15 mmol:2-10 mL, wherein the concentration of the hydrochloric acid solution is 1-4 mol / L.

[0014] Preferably, in step (2), the molar volume ratio of the iron salt to water is 15-25 mmol:20-60 mL.

[0015] Preferably, the molar volume ratio of the iron salt to the isopropanolamine solution is 15-25 mmol:150-250 mL; and the concentration of the isopropanolamine solution is 2-4 mol / L.

[0016] Preferably, in step (3), the reaction temperature is 80 to 120° C., and the reaction time is 1 to 3 hours.

[0017] The present invention provides an amorphous iron-manganese-oxygen cluster prepared by the above-mentioned method for preparing the amorphous iron-manganese-oxygen cluster.

[0018] The present invention provides an application of the above-mentioned amorphous iron manganese oxygen cluster enhanced functional enzyme to produce methane, comprising the following steps: adding the amorphous iron manganese oxygen cluster dispersion liquid to the mixed bacterial granular sludge to perform activation treatment and anaerobic digestion in sequence;

[0019] The mixed bacterial granular sludge contains Actinomycetota and Euryarchaeota.

[0020] Preferably, the volume ratio of the amorphous ferromanganese cluster dispersion liquid to the mixed bacterial granular sludge is 5-10:20-40; and the concentration of the amorphous ferromanganese cluster dispersion liquid is 0.4-0.5 g / L.

[0021] Preferably, during the activation treatment, the pH value is first adjusted to 7.3-7.5, and then the activation treatment is performed at a temperature of 30-40° C. until the pH value fluctuation of the system is less than 0.1 or the pH value of the system is lower than 3.5, and the activation treatment is completed.

[0022] Preferably, the pH value is adjusted to 7.0-7.2 before the anaerobic digestion and then the anaerobic digestion is started.

[0023] Beneficial effects of the present invention:

[0024] (1) The present invention synthesizes amorphous iron manganese oxygen clusters (FMOc) and adds them to the anaerobic reaction system of the target bacterial community. They can be absorbed into the cells through the microbial "eating" process, stimulating the activity of iron-sulfur protein oxidoreductase (FTR). The anaerobic methanogenesis process is enhanced through the interaction of FTR-FMOc, and the methane production and the ratio of methane to carbon dioxide are simultaneously increased. The amorphous iron manganese oxygen clusters after absorption can achieve efficient utilization of carbon sources in the anaerobic system and long-lasting and long-lasting methane production.

[0025] (2) Amorphous iron-manganese oxygen clusters have the functions of electron transfer and storage, which can construct a direct electron transfer pathway between bacteria and archaea, replacing the traditional indirect electron transfer mediated by H2 and HCOOH. They can be used as buffers in anaerobic digestion, eliminating the effects of intermediate acids on the methanogenesis process by chelation or adsorption.

[0026] (3) Amorphous iron manganese oxygen clusters are used to simulate the function of cytochrome, increase the adenine nucleoside triphosphate (ATP) production of archaea, accelerate the growth of archaea, and balance the growth difference between them and acidogenic bacteria. This shows that the amorphous iron manganese oxygen clusters of the present invention can efficiently activate the methanogenic efficiency of functional enzyme genes in the anaerobic system, and solve the technical problems of low carbon source utilization and system instability caused by severe acidification in conventional anaerobic systems.

[0027] (4) The preparation method of the amorphous iron-manganese oxygen cluster provided by the present invention is simple, environmentally friendly, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The physicochemical characterization diagrams of the amorphous iron-manganese oxygen cluster prepared in Example 1, wherein A is a high-resolution transmission electron microscope diagram, and B and C are elemental analysis diagrams;

[0029] Figure 2 The graphs of COD concentration and methane cumulative production during anaerobic digestion in Application Example 1 as a function of anaerobic digestion time are shown in Figure 1, where A is a graph of COD concentration as a function of anaerobic digestion time, and B is a graph of methane cumulative production as a function of anaerobic digestion time;

[0030] Figure 3 The electron microscope analysis diagrams and elemental analysis diagrams of the mixed bacteria granular sludge after anaerobic digestion in Application Example 1 and Application Comparative Example 1 are shown in FIG. A is the electron microscope analysis diagram of the mixed bacteria granular sludge after anaerobic digestion in Application Comparative Example 1, B is the elemental analysis diagram of the mixed bacteria granular sludge after anaerobic digestion in Application Comparative Example 1, C is the electron microscope analysis diagram of the mixed bacteria granular sludge after anaerobic digestion in Application Example 1, and D is the elemental analysis diagram of the mixed bacteria granular sludge after anaerobic digestion in Application Example 1;

[0031] Figure 4 A comparison chart of the differences in microbial community composition and the expression differences of key functional genes in the mixed granular sludge after anaerobic digestion in Application Example 1 and Application Comparative Example 1, wherein A is a comparison chart of the differences in microbial community composition in the mixed granular sludge after anaerobic digestion in Application Example 1 and Application Comparative Example 1, and B is a comparison chart of the expression differences of functional genes related to the archaeal methanogenesis and carbon fixation pathways in the mixed granular sludge after anaerobic digestion in Application Example 1 and Application Comparative Example 1. DETAILED DESCRIPTION

[0032] The present invention provides a method for preparing an amorphous iron-manganese-oxygen cluster, comprising the following steps:

[0033] (1) mixing a manganese salt and a hydrochloric acid solution to obtain a hydrochloric acid solution of a manganese salt;

[0034] (2) dissolving iron salt in water to obtain an iron salt solution;

[0035] (3) A hydrochloric acid solution of a manganese salt and an iron salt solution are mixed and heated, and then an isopropanolamine solution is added to react to obtain an amorphous iron-manganese oxide cluster.

[0036] In the present invention, in the step (1), the molar volume ratio of the manganese salt to the hydrochloric acid solution is 5-15 mmol:2-10 mL, preferably 8-12 mmol:3-8 mL, and more preferably 10 mmol:5-6 mL, wherein the concentration of the hydrochloric acid solution is 1-4 mol / L, preferably 2-3 mol / L, and more preferably 2.4-2.6 mol / L.

[0037] The present invention has no particular limitation on the type of the manganese salt, as long as it is a manganese salt that can be dissolved in a hydrochloric acid solution. In the embodiment of the present invention, manganese chloride is preferably used.

[0038] In the present invention, in step (2), the molar volume ratio of the iron salt to water is 15-25 mmol:20-60 mL, preferably 18-22 mmol:30-50 mL, and more preferably 20 mmol:40 mL.

[0039] The present invention has no particular limitation on the type of the iron salt, as long as it is an iron salt that can be dissolved in water. In the embodiment of the present invention, ferric chloride is preferably used.

[0040] In the present invention, the hydrochloric acid solution of the manganese salt and the iron salt solution are preferably heated to 50° C. and then mixed, the obtained mixed solution is further heated to 100° C., and then the isopropanolamine solution is quickly added.

[0041] In the present invention, the molar volume ratio of the iron salt to the isopropanolamine solution is 15-25 mmol:150-250 mL, preferably 18-22 mmol:180-220 mL, and more preferably 20 mmol:200 mL; the concentration of the isopropanolamine solution is 2-4 mol / L, preferably 2.5-3.5 mol / L, and more preferably 3 mol / L.

[0042] In the present invention, in step (3), the reaction temperature is 80 to 120° C., preferably 90 to 110° C., more preferably 100° C., and the reaction time is 1 to 3 h, preferably 1.5 to 2.5 h, more preferably 2 h.

[0043] In the present invention, the reaction product is preferably cooled, centrifuged, washed and dried in sequence to obtain amorphous iron-manganese oxide clusters.

[0044] In the present invention, the amorphous iron-manganese oxide cluster is preferably dispersed in a tetramethylammonium hydroxide aqueous solution and stored for later use.

[0045] The present invention selects tetramethylammonium hydroxide aqueous solution as a dispersant, which has the following advantages: (1) high efficiency, tetramethylammonium hydroxide has good solubility in water, can effectively reduce the surface tension of the liquid, and thus improve the dispersion effect; (2) wide applicability, the tetramethylammonium hydroxide aqueous solution is suitable for various types of particles and liquids; (3) environmental friendliness, compared with certain organic solvents, tetramethylammonium hydroxide has less impact on the environment and is more safe; (4) good stability; (5) providing an alkaline environment, which is conducive to the formation and stable preservation of amorphous iron-manganese oxygen clusters.

[0046] The present invention provides an amorphous iron-manganese-oxygen cluster prepared by the above-mentioned method for preparing the amorphous iron-manganese-oxygen cluster.

[0047] The present invention provides an application of the above-mentioned amorphous iron manganese oxygen cluster enhanced functional enzyme to produce methane, comprising the following steps: adding the amorphous iron manganese oxygen cluster dispersion liquid to the mixed bacterial granular sludge to perform activation treatment and anaerobic digestion in sequence;

[0048] The mixed bacterial granular sludge contains Actinomycetota and Euryarchaeota.

[0049] In the present invention, the volume ratio of the amorphous ferromanganese cluster dispersion liquid to the mixed bacterial granular sludge is 5-10:20-40; the concentration of the amorphous ferromanganese cluster dispersion liquid is 0.4-0.5 g / L.

[0050] In the present invention, during the activation treatment, the pH value is first adjusted to 7.3-7.5, and then the activation treatment is performed at a temperature of 30-40° C. until the pH value fluctuation of the system is less than 0.1 or the pH value of the system is lower than 3.5.

[0051] In the present invention, the pH value is adjusted to 7.0-7.2 before the anaerobic digestion and then the anaerobic digestion is started.

[0052] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0053] The mixed granular sludge used in the embodiment of the present invention comes from the expanded granular sludge bed reactor of Guangxi Yipu Environmental Engineering Co., Ltd., wherein the abundance of Actinomycetota is 37.90%, the abundance of Euryarchaeota is 13.66%, and the COD removal load of the mixed granular sludge is preferably set to 5.45 kg COD / L·d; the concentration of suspended solids (SS) in the mixed granular sludge is 44.8 g SS / L, and the concentration of volatile suspended solids (VSS) is 36.89 g VSS / L.

[0054] Example 1

[0055] 10mmol of MnCl2·4H2O was dissolved in 5mL of hydrochloric acid solution (concentration of 2.4mol / L) to obtain a hydrochloric acid solution of manganese chloride; 20mmol of FeCl3·6H2O was dissolved in 40mL of deionized water to obtain a ferric chloride solution; then the above two solutions were heated to 50°C and mixed and quickly mechanically stirred, and when the temperature of the mixed solution was continued to be heated to 100°C, 200mL of isopropanolamine solution (concentration of 3mol / L) was quickly added, and the reaction was continued to be stirred at 100°C for 2h. After the reaction was completed, the reaction mixture was cooled to room temperature, and then the brown precipitate was separated by a high-speed centrifuge, and the brown precipitate was washed with anhydrous ethanol, and finally placed in a vacuum dryer at 60°C for 48h to obtain an amorphous iron manganese oxygen cluster. The amorphous iron manganese oxygen cluster prepared above was dispersed in a tetramethylammonium hydroxide aqueous solution with a concentration of 0.1mol / L and stored for use.

[0056] Example 2

[0057] 15mmol of MnCl2·4H2O was dissolved in 10mL of hydrochloric acid solution (concentration of 4mol / L) to obtain a hydrochloric acid solution of manganese chloride; 25mmol of FeCl3·6H2O was dissolved in 60mL of deionized water to obtain a ferric chloride solution; then the above two solutions were heated to 50°C and mixed and quickly mechanically stirred, and when the temperature of the mixed solution was continued to be heated to 100°C, 250mL of isopropanolamine solution (concentration of 4mol / L) was quickly added, and the reaction was continued to be stirred at 80°C for 1h. After the reaction was completed, the reaction mixture was cooled to room temperature, and then the brown precipitate was separated by a high-speed centrifuge, and the brown precipitate was washed with anhydrous ethanol, and finally placed in a vacuum dryer at 60°C for 48h to obtain an amorphous iron manganese oxygen cluster. The amorphous iron manganese oxygen cluster prepared above was dispersed in a tetramethylammonium hydroxide aqueous solution with a concentration of 0.1mol / L and stored for use.

[0058] Example 3

[0059] 5mmol of MnCl2·4H2O was dissolved in 3mL of hydrochloric acid solution (concentration of 1mol / L) to obtain a hydrochloric acid solution of manganese chloride; 15mmol of FeCl3·6H2O was dissolved in 20mL of deionized water to obtain a ferric chloride solution; then the above two solutions were heated to 50°C and mixed and quickly mechanically stirred, and when the temperature of the mixed solution was continued to be heated to 100°C, 150mL of isopropanolamine solution (concentration of 2mol / L) was quickly added, and the reaction was continued to be stirred at 120°C for 3h. After the reaction was completed, the reaction mixture was cooled to room temperature, and then the brown precipitate was separated by a high-speed centrifuge, and the brown precipitate was washed with anhydrous ethanol, and finally placed in a vacuum dryer at 60°C for 48h to obtain an amorphous iron manganese oxygen cluster. The amorphous iron manganese oxygen cluster prepared above was dispersed in a tetramethylammonium hydroxide aqueous solution with a concentration of 0.1mol / L and stored for use.

[0060] Figure 1 The physicochemical characterization diagram of the amorphous iron-manganese oxygen cluster prepared in Example 1 is shown in FIG. Figure 1 It can be seen that Mn and Fe elements exist in an amorphous form, and Fe element bonds with Mn in the form of oxygen bridge bonds to form FeMn oxygen cluster substances.

[0061] Application Example 1

[0062] Mixed granular sludge was selected as the target sludge, in which the abundance of Actinomycetota was 37.9%, the abundance of Euryarchaeota was 13.66%, the COD removal load of the mixed granular sludge was set to 5.45 kg COD / L·d, the concentration of suspended solids (SS) was 44.8 g SS / L, and the concentration of volatile suspended solids (VSS) was 36.89 g VSS / L. The mixed granular sludge was placed in a 120 mL anaerobic bottle, and the inoculation amount of the mixed granular sludge was 30 mL.

[0063] The amorphous iron manganese oxyclusters (the amorphous iron manganese oxyclusters prepared in Example 1 above) dispersed in the tetramethylammonium hydroxide aqueous solution were centrifuged and washed three times with anhydrous ethanol, and then placed in a vacuum dryer and dried at 60° C. for 48 h. After drying, 0.45 g of the amorphous iron manganese oxyclusters was weighed and added to 100 mL of deionized water, ultrasonically dispersed for 30 min, and then 8 mL of the dispersion was added to the above-mentioned anaerobic bottle to form an anaerobic digestion system.

[0064] The pH value of the anaerobic digestion system was adjusted to 7.3-7.5 with sodium hydroxide solution (concentration of 1 mol / L), COD in the wastewater was 5000 mg / L, C / N / P ratio was 200 / 5 / 1, nitrogen was blown off for 5 minutes, rubber plug was used to seal, connected to a 500 mL air bag through a connecting device, placed in a constant temperature environment of 35°C, water and gas samples were taken every 2 hours, and the sealing state was maintained during the sampling period. When the pH value in the system was measured to be stable (fluctuation less than 0.1 within 2 hours) or the pH value of the system was lower than 3.5, the activation treatment process was completed. Then the pH of the system was adjusted to about 7.0-7.2 with sodium hydroxide solution (concentration of 1 mol / L), and anaerobic digestion was started. Subsequently, water and gas samples were taken every 24 hours, and the sealing state was maintained throughout the sampling period. When the COD concentration in the water sample was stable, the anaerobic digestion process was completed and mud samples were taken.

[0065] Application Comparative Example 1

[0066] The difference from Application Example 1 is that the dispersion of amorphous iron-manganese oxygen clusters is not added to the anaerobic digestion system.

[0067] Figure 2 The figure is a graph showing the changes of COD concentration and methane cumulative production during anaerobic digestion with anaerobic digestion time. In the figure, C represents comparative application example 1, M represents application example 1, and Figure 2 It can be seen that when amorphous iron manganese oxygen clusters are added to the anaerobic digestion system, the cumulative methane production in the system is lower than that of the anaerobic digestion system without adding amorphous iron manganese oxygen clusters (Comparative Application Example 1) after 24 hours of anaerobic digestion. After 48 hours, the cumulative methane production is slightly higher than that of the anaerobic digestion system without adding amorphous iron manganese oxygen clusters (Comparative Application Example 1). After 72 hours of anaerobic digestion, the cumulative methane production is much higher than that of the anaerobic digestion system without adding amorphous iron manganese oxygen clusters (Comparative Application Example 1). This shows that the amorphous iron manganese oxygen clusters prepared by the present invention can increase the ATP production of archaea and accelerate the growth of archaea.

[0068] Take the mud samples after the anaerobic digestion in Application Example 1 and Application Comparative Example 1, use 1% agarose gel electrophoresis to detect the genomic DNA of the extracted granular sludge, and then use Covaris M220 to fragment the genomic DNA. Then construct the PE library, and the specific operations are as follows: connect the "Y"-shaped connector; use magnetic beads to screen and remove the self-connected fragments of the connector; use PCR amplification to enrich the library template; sodium hydroxide denaturation to produce single-stranded DNA fragments. Finally, use Illumina sequencing to obtain the sequence of the template DNA fragment. The original sequence is optimized by splitting, quality shearing, and removing contamination. Then use the optimized sequence for splicing assembly and gene prediction, and annotate and classify the obtained genes in terms of species and function. At the same time, the sludge samples are freeze-dried and sliced, and then analyzed by electron microscopy.

[0069] Figure 3 The electron microscope analysis and elemental analysis of the mixed bacterial granular sludge after anaerobic digestion in Application Example 1 and Comparative Example 1 are shown in FIG. Figure 3 As can be seen from Figures A and B, the Fe and Mn elements of the target bacteria are evenly distributed inside and around the cells. Figure 3 As can be seen from Figures C and D, the amorphous iron-manganese-oxygen clusters have entered the target bacteria, and the iron-manganese-oxygen clusters are distributed inside the cells and in the cell membrane.

[0070] from Figure 4 It can be seen that amorphous iron-manganese oxygen clusters enhance the methanogenic archaea in mixed bacterial granular sludge and achieve a rapid increase in their abundance. At the same time, the functional gene table of each methanogenic pathway in the archaea is normalized and expressed by Log2TPM. The intervention of amorphous iron-manganese oxygen clusters significantly improves the expression of functional genes related to methanogenesis and its carbon fixation capacity. Figure 4 C represents comparative application example 1, and M represents application example 1.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing an amorphous iron-manganese-oxygen cluster, characterized in that: The steps include: (1) mixing a manganese salt and a hydrochloric acid solution to obtain a hydrochloric acid solution of a manganese salt; (2) dissolving iron salt in water to obtain an iron salt solution; (3) A hydrochloric acid solution of a manganese salt and an iron salt solution are mixed and heated, and then an isopropanolamine solution is added to react to obtain an amorphous iron-manganese oxide cluster.

2. The method for preparing amorphous iron-manganese-oxygen clusters according to claim 1, characterized in that: In the step (1), the molar volume ratio of the manganese salt to the hydrochloric acid solution is 5-15 mmol:2-10 mL, wherein the concentration of the hydrochloric acid solution is 1-4 mol / L.

3. The method for preparing amorphous iron-manganese-oxygen clusters according to claim 1 or 2, characterized in that: In the step (2), the molar volume ratio of the iron salt to water is 15-25 mmol:20-60 mL.

4. The method for preparing amorphous iron-manganese oxygen clusters according to claim 3, characterized in that: The molar volume ratio of the iron salt to the isopropanolamine solution is 15-25 mmol:150-250 mL; the concentration of the isopropanolamine solution is 2-4 mol / L.

5. The method for preparing amorphous iron-manganese oxide clusters according to claim 1, 2 or 4, characterized in that: In the step (3), the reaction temperature is 80 to 120° C. and the reaction time is 1 to 3 hours.

6. Amorphous iron-manganese-oxide clusters obtained by the method for preparing amorphous iron-manganese-oxide clusters according to any one of claims 1 to 5.

7. The use of the amorphous iron-manganese-oxygen cluster enhanced functional enzyme to produce methanogen according to claim 6, characterized in that: The method comprises the following steps: adding amorphous iron-manganese oxygen cluster dispersion liquid into mixed bacterial granular sludge to perform activation treatment and anaerobic digestion in sequence; The mixed bacterial granular sludge contains Actinomycetota and Euryarchaeota.

8. The use of amorphous iron-manganese-oxygen cluster enhanced functional enzyme to produce methanogen according to claim 7, characterized in that: The volume ratio of the amorphous iron-manganese-oxygen cluster dispersion liquid to the mixed bacterial granular sludge is 5-10:20-40; the concentration of the amorphous iron-manganese-oxygen cluster dispersion liquid is 0.4-0.5 g / L.

9. The use of amorphous iron-manganese-oxygen cluster enhanced functional enzyme to produce methanogen according to claim 7 or 8, characterized in that: During the activation treatment, the pH value is first adjusted to 7.3-7.5, and then the activation treatment is performed at a temperature of 30-40° C. until the pH value fluctuation of the system is less than 0.1 or the pH value of the system is lower than 3.5, at which time the activation treatment is completed.

10. The use of amorphous iron-manganese-oxygen cluster enhanced functional enzyme to produce methanogen according to claim 9, characterized in that: Before the anaerobic digestion, the pH value is adjusted to 7.0-7.2 and then the anaerobic digestion is started.

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