A method for promoting the enrichment of methanothrix and / or lactic acid bacteria in an anaerobic digestion system of food waste

Abstract

The present invention discloses a method for promoting the enrichment of methanothrix and / or lactic acid bacteria in an anaerobic digestion system for food waste, belonging to the technical field of anaerobic digestion. The present invention optimizes the microbial community by rationally adding cobalt-modified biochar to the anaerobic digestion system for food waste, enhancing the activity of specific microorganisms and effectively promoting the anaerobic digestion process of organic waste such as food waste. By modifying the biochar with divalent cobalt ions, the enrichment of lactic acid bacteria and methanothrix in the anaerobic digestion system for food waste is increased, and biogas production is also increased, which is of great significance for optimizing the anaerobic fermentation process and increasing biogas production.

Description

Technical Field

[0001] The present invention belongs to the technical field of anaerobic digestion, and in particular relates to a method for promoting the enrichment of methanothrix and / or lactic acid bacteria in an anaerobic digestion system of food waste. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Anaerobic digestion of food waste is widely used to convert organic waste into renewable energy sources such as biogas. This process is of great significance for reducing the environmental impact of organic waste and realizing waste resource utilization. In anaerobic digestion systems, the presence and activity of specific microbial populations are crucial to the success of the entire fermentation process. Anaerobic digestion is a complex, multi-step biochemical process that includes hydrolysis, acidification, acetogenesis, and methanogenesis, each of which relies on the participation of specific microorganisms. Each microbial population plays a unique role in the anaerobic digestion system and is interdependent and synergistic with each other to maintain the function and stability of the system. Currently, many studies have found that specific microbial populations not only promote the degradation and transformation of organic matter during anaerobic digestion, but also ensure the stability and efficiency of the system by maintaining the system's acid-base balance, regulating metabolite concentrations, and preventing the accumulation of inhibitory substances.

[0004] In anaerobic food waste digestion systems, Lactobacilli can participate in direct electron transfer. The lactic acid they produce can be promptly converted into VFAs, providing sufficient substrate for anaerobic fermentation and increasing biogas production. Methanothrix has been shown to be one of the most common microorganisms involved in direct electron transfer and is associated with increased methane production. Enriching Lactobacilli and Methanothrix in anaerobic food waste digestion systems is crucial for increasing biogas production. Summary of the Invention

[0005] In order to address the deficiencies of the prior art, the present invention aims to provide a method for promoting the enrichment of methanogenic bacteria and / or lactic acid bacteria in the anaerobic digestion system of food waste. The present invention achieves the enhancement and enrichment of the activity of specific microorganisms such as lactobacilli and methanogenic bacteria in the anaerobic digestion system of food waste, thereby increasing the biogas production during the anaerobic digestion process.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] In a first aspect, the present invention provides a method for enriching methanothrix and / or lactic acid bacteria in an anaerobic digestion system of food waste, wherein cobalt-modified biochar is added to the anaerobic digestion system of food waste, and the concentration of the cobalt-modified biochar in the anaerobic digestion system of food waste is 1 to 5 g / L.

[0008] In some embodiments of the present invention, the method for preparing cobalt-modified biochar comprises the following steps:

[0009] Under a protective atmosphere, food digestate is pyrolyzed to obtain biochar, which is then immersed in a cobalt salt solution, taken out, washed, and dried to obtain cobalt-modified biochar.

[0010] In some embodiments of the present invention, the protective atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0011] In some embodiments of the present invention, the pyrolysis is carried out at a temperature of 500-600° C., for a time of 1-3 h, and a heating rate of 3-7° C. / min.

[0012] In some embodiments of the present invention, after pyrolysis is completed, the biochar is washed, dried, sieved, and collected with a particle size of less than 150 mesh, and then immersed in a cobalt salt solution.

[0013] In some embodiments of the present invention, the washing is performed using ethanol and water.

[0014] Preferably, the drying temperature is 100-110° C. and the drying time is 10-15 h.

[0015] In some embodiments of the present invention, the concentration of cobalt ions in the cobalt salt solution is 0.05-0.15 M, the ratio of biochar to cobalt salt solution is 1 g:9-11 mL, and the biochar is oscillated in the cobalt salt solution at 25-30° C. and 130-150 rpm / min for 20-25 h.

[0016] In some embodiments of the present invention, the drying is freeze-drying.

[0017] A second aspect of the present invention provides the use of cobalt-modified biochar in promoting the enrichment of methanothrix and / or lactic acid bacteria in an anaerobic digestion system for food waste.

[0018] In some embodiments of the present invention, the application is adding 1-5 g / L of cobalt-modified biochar to the anaerobic digestion system of food waste.

[0019] The beneficial effects of the present invention are:

[0020] The present invention provides a method for promoting the enrichment of methanothrix and / or lactic acid bacteria in an anaerobic digestion system for food waste. Biochar is a high-carbon material with properties such as a high specific surface area, a porous structure, and good electrical conductivity. These properties enable biochar to effectively improve the anaerobic digestion process by enriching microorganisms. Cobalt ions are essential trace elements for the growth and metabolism of many anaerobic microorganisms and play a key role in the synthesis of various enzymes and cofactors. This method optimizes the microbial community by rationally adding cobalt to modified biochar, enhancing the activity of specific microorganisms such as lactobacilli and methanothrix, effectively promoting the anaerobic digestion of organic waste such as food waste. This study investigates the use of divalent cobalt ion-modified biochar to enhance the enrichment of specific microorganisms (lactic acid bacteria and methanothrix) in anaerobic digestion systems for food waste, thereby increasing biogas production. This approach is of great significance for optimizing the anaerobic fermentation process and increasing biogas production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0022] Figure 1 SEM images and EDS images of the cobalt-modified biochar and unmodified biochar prepared in Example 1 of the present invention, wherein a is the SEM image of the unmodified biochar, b is the SEM image of the cobalt-modified biochar, c is the EDS image of the unmodified biochar, and d is the EDS image of the cobalt-modified biochar;

[0023] Figure 2 Graph showing the diversity index of microorganisms in the three reactors in Example 2;

[0024] Figure 3 This is the microbial richness diagram at the bacterial phylum level for the three reactors in Example 2;

[0025] Figure 4 This is the microbial richness diagram at the bacterial genus level for the three reactors in Example 2;

[0026] Figure 5 This is the microbial richness diagram at the Archaea level in the three reactors in Example 2. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0028] Example 1 Preparation of cobalt-modified biochar

[0029] The preparation procedures for unmodified biochar (DDB) and cobalt-modified biochar (DDB-CoCl2) are described below. Prior to pyrolysis, the air in the tube furnace was purged with nitrogen at a rate of 0.2 L / min for 30 minutes to ensure an oxygen-free environment. Next, ground food digestate was placed in a quartz boat within the tube furnace. The temperature was increased from room temperature (30°C) to 550°C at a heating rate of 5°C / min and maintained at this temperature for 2 hours. Throughout the pyrolysis process, nitrogen was continuously introduced at 0.2 L / min to maintain oxygen-free conditions until the tube furnace naturally cooled to room temperature. After the furnace temperature dropped to ambient temperature, the product was removed from the furnace. The resulting biochar was washed multiple times with ethanol and deionized water and then filtered. The washed biochar was dried at 105°C for 12 hours and sieved through a 150-mesh sieve. Biochar with a particle size less than 150 mesh (i.e., unmodified biochar) was collected and sealed for storage.

[0030] For cobalt modification, 0.1 mol / L CoCl2·6H2O solution was prepared in advance. Every 10 g of biochar powder was soaked in 100 mL of the desired concentration of CoCl2·6H2O solution. 2+ The container was wrapped with tinfoil and placed in a thermostatic oscillator set at 30°C and 140 rpm for 24 hours. The biochar was then separated from the solution using a 0.45 µm membrane filter and thoroughly rinsed several times with deionized water. The washed biochar was frozen at -80°C for several hours and then freeze-dried using a freeze dryer to obtain cobalt-modified biochar (DDB-CoCl2). The modified biochar should be sealed and stored for experimental use.

[0031] Figure 1 The SEM characterization and EDS images of unmodified biochar (DDB) and cobalt-modified biochar are shown in Figure 2. Figure 1 (d) with Figure 1 (c) Comparison shows that cobalt ions are loaded on biochar, proving that the modification is successful.

[0032] Example 2 Anaerobic digestion reactor and operation

[0033] The experimental apparatus consisted of an aluminum foil double-valve gas collection bag, a 500 mL digestion bottle with a working volume of 400 mL, and a constant temperature shaking incubator. The gas collection bag and digestion bottle were connected with silicone tubing to form an anaerobic reactor. Experiments were conducted in three anaerobic reactors, each consisting of three digestion bottles. Each digestion bottle was loaded with 300 mL of food waste and 100 mL of inoculum to maintain a 3:1 (volume ratio) mixing ratio. The initial pH of each reactor was adjusted to 7.0 ± 0.2 using 4 mol / L NaOH and HCl. Subsequently, 0 g / L DDB, 4 g / L DDB, and 4 g / L DDB-CoCl2 were added to the three digestion bottles, respectively. The three bottles were designated CK, 4 g / L DDB, and 4 g / L DDB-CoCl2. After all materials were added, each bottle was purged with nitrogen for approximately 2 minutes to ensure anaerobic conditions. For the next 45 days of anaerobic digestion, all bottles were incubated in a constant-temperature shaker at 30 ± 1°C and 140 rpm / min. Gas content in the sampling bag was recorded daily throughout the anaerobic digestion process. The reaction was considered terminated when no significant increase in biogas accumulation was observed in the reactor. On day 45, 50 mL of digestion samples were collected from the CK, 4 g / L DDB, and 4 g / L DDB-CoCl2 reactors, stored frozen, and shipped to Shanghai Meiji Biopharmaceutical Technology Co., Ltd. for microbial community analysis.

[0034] Analysis of microbial community composition in anaerobic digestion systems in three reactors

[0035] Figure 2 The Alpha diversity of bacteria in the three groups is shown. The microbial richness at the phylum and genus levels is shown in Figure 2. Figure 3 and Figure 4 shown. Figure 5 It reflects the changes in bacterial species in the archaeal community.

[0036] Depend on Figure 2 The Chao index for CK, 4 g / L DDB, and 4 g / L DDB-CoCl2 was 184.80, 172.05, and 114.14, respectively. The ACE index for CK, 4 g / L DDB, and 4 g / L DDB-CoCl2 was 187.70, 176.12, and 110.28, respectively. The Simpon index for these three groups was 0.08, 0.10, and 0.14, respectively. These results suggest that 4 g / L DDB-CoCl2 reduced microbial richness and diversity, likely because 4 g / L DDB-CoCl2 promoted the growth of specific microbial groups that dominated the environment and inhibited the growth of other microorganisms.

[0037] Depend on Figure 3(Explanation of changes at the bacterial phylum level) It can be seen that Firmicutes ( Firmicutes ), Actinomycetes ( Actinobacteriota ) and Proteobacteria ( Proteobacteria ) and other typical anaerobic fermentation bacteria were the dominant phyla in the three groups, accounting for more than 99.9% of the total. However, 4 g / L DDB-CoCl2 could change the relative abundance of microorganisms at the phylum level. Firmicutes ( Firmicutes ) accounted for 77.23% in the CK group, 99.98% in 4 g / L DDB and 99.89% in 4 g / L DDB-CoCl2, respectively, which indicated that the addition of DDB and DDB-CoCl2 enhanced the growth of Firmicutes. (Firmicutes ) advantage, which can be attributed to the fact that the high solid content reaction environment is conducive to its growth and the huge specific surface area and porous structure of biochar provide it with a rich habitat. Actinobacteriota ) has the natural ability to degrade complex organic matter and can degrade complex polysaccharides into VFAs. It accounted for the highest proportion in the CK group, reaching 22.7%, higher than the other two groups.

[0038] Depend on Figure 4 (Explanation at the bacterial genus level) It can be seen that the changes in microbial community structure emphasize the potential role of biochar in promoting the proliferation of specific microorganisms. In the 4 g / L DDB-CoCl2 group, the largest proportion was Lactobacillus (Lactobacillus ), with a relative abundance of approximately 86.3%, significantly higher than that of CK (26.0%) and 4 g / L DDB (41.6%). Furthermore, the addition of DDB-Co selectively improved the adaptability of Lactobacilli and enabled them to participate in direct electron transfer, allowing them to promptly convert their lactic acid into VFAs, providing sufficient substrate for anaerobic fermentation. This also contributed to the increased biogas production. This suggests that the addition of DDB-Co further strengthened the dominant bacterial genera.

[0039] Depend on Figure 5 (Explanation at the Archaea level) It can be seen that methanogens play a vital role in the methane production process. Figure 5 The effect of DDB-Co on the relative abundance of Archaea at the genus level was demonstrated. Compared with CK, Methanobacterium ( Methanolobus ), Methanothrix ( Methanothrix ) and Methanobrevibacterium ( Methanobrevibacter ) increased significantly in the group after adding DDB and DDB-Co, becoming the dominant bacterial genus. Specifically, Methanothrix ( Methanothrix ) and Methanobrevibacterium ( Methanobrevibacter) in the 4 g / L DDB group were 4.9% and 2.2%, respectively, while their relative abundances in the 4 g / L DDB-CoCl2 group increased to 15.2% and 3.7%. Methanolobus ) is a methylotrophic methanogen that can effectively convert methanol, methylamine and other methyl compounds into methane; Methanothrix ( Methanothrix ) are acetotrophic methanogens that produce methane through the acetate decarboxylation pathway; Methanobrevibacterium ( Methanobrevibacter) It is a hydrogenotrophic methanogen that produces methane using H2 and CO2. Methanothrix ) has been shown to be one of the most common microorganisms involved in direct electron transfer, and its relative abundance in the 4 g / L DDB-CoCl2 group was much higher than that in the other two groups. This indicates that the presence of DDB-Co can effectively increase the diversity of archaea and selectively enrich Methanothrix ( Methanothrix ) and other functional microorganisms, thereby increasing the system's biogas production.

[0040] In summary, the microbial community structure analysis showed that DDB-Co reduced microbial richness and diversity, but enhanced the microbial diversity by selectively enriching Lactobacillus spp. (Lactobacillus ) and Methanothrix ( Methanothrix ) and other microorganisms, which accelerate the system reaction rate and thus increase biogas production.

[0041] 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 enriching lactic acid bacteria in an anaerobic digestion system of food waste, characterized in that: Cobalt-modified biochar is added to the anaerobic digestion system of food waste, and the concentration of cobalt-modified biochar in the anaerobic digestion system of food waste is 1-5 g / L; the lactic acid bacteria are Lactobacillus ( Lactobacillus ); The preparation method of the cobalt-modified biochar comprises the following steps: Under a protective atmosphere, food digestate is pyrolyzed to obtain biochar, which is then immersed in a cobalt salt solution, taken out, washed, and dried to obtain cobalt-modified biochar.

2. A Methanothrix in an Anaerobic Digestion System for Food Waste ( Methanothrix ) and a method for enriching lactic acid bacteria, characterized in that, Cobalt-modified biochar is added to the anaerobic digestion system of food waste, and the concentration of cobalt-modified biochar in the anaerobic digestion system of food waste is 1-5 g / L; the lactic acid bacteria are Lactobacillus ( Lactobacillus ); The preparation method of the cobalt-modified biochar comprises the following steps: Under a protective atmosphere, food digestate is pyrolyzed to obtain biochar, which is then immersed in a cobalt salt solution, taken out, washed, and dried to obtain cobalt-modified biochar.

3. The method according to claim 1 or 2, wherein: The protective atmosphere is a nitrogen atmosphere or an argon atmosphere.

4. The method according to claim 1 or 2, wherein: The pyrolysis temperature is 500-600° C., the time is 1-3 hours, and the heating rate is 3-7° C. / min.

5. The method according to claim 1 or 2, wherein: After pyrolysis is completed, the biochar with a particle size of less than 150 mesh is washed, dried, and sieved to collect the biochar, which is then immersed in a cobalt salt solution.

6. The method according to claim 5, wherein The washing is carried out using ethanol and water.

7. The method according to claim 5, wherein The drying temperature is 100-110° C. and the time is 10-15 hours.

8. The method according to claim 1 or 2, wherein: The concentration of cobalt ions in the cobalt salt solution is 0.05-0.15 M, the ratio of biochar to cobalt salt solution is 1 g:9-11 mL, and the biochar is shaken in the cobalt salt solution at 25-30° C. and 130-150 rpm / min for 20-25 h.

9. The method according to claim 1 or 2, wherein: The drying is freeze-drying.

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