Application of sponge iron synergistic compound bacteria in aerobic composting of cow dung

Abstract

The invention provides an application of sponge iron synergistic compound bacteria in cow dung aerobic composting, and belongs to the technical field of cow dung composting. According to the application of the sponge iron synergistic compound bacteria in aerobic composting of cow dung, the compound bacteria comprise bacillus subtillis and lysinibacillus fusiformis. The sponge iron and the compound bacteria are added into the cow dung aerobic compost, so that the compost temperature can be increased, and the compost process is accelerated; the degradation of organic matters can be promoted and the humification degree of compost can be improved. In addition, the microbial community structure can be optimized, and the diversity and richness of bacterial communities in the composting process are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of cow dung composting, and particularly relates to application of sponge iron synergistic composite bacteria in aerobic composting of cow dung. Background Art

[0002] In recent years, the livestock farming industry has developed rapidly, and the amount of livestock and poultry manure produced has increased dramatically, which has had an adverse impact on soil, water and air quality, and threatened ecological sustainability. Cow dung, as the main type of manure, accounts for 45.8% of total livestock waste. Cow dung is a rich source of organic fertilizer and is rich in essential nutrients. However, direct application without treatment can easily breed mosquitoes and increase pathogenic bacteria. Aerobic composting is a common method for treating cow dung. However, cow dung contains a high content of difficult-to-degrade lignocellulose, which leads to long composting cycles, low humification levels, and poor final product quality. This directly reduces the fertilization effect of the compost product, and the heavy metals therein are not effectively passivated. Therefore, it is crucial to find methods that can improve the efficiency of the cow dung composting process and improve the quality of the final product. Summary of the Invention

[0003] In view of this, one of the objects of the present invention is to provide an application of sponge iron synergistic composite bacteria in aerobic composting of cow dung, which can improve the composting efficiency and maturity of cow dung compost and improve the compost quality.

[0004] A second object of the present invention is to provide a method for aerobic composting of cow dung, which has the advantages of high composting efficiency, high compost maturity and high compost quality.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The invention provides application of sponge iron synergistic composite bacteria in aerobic composting of cow dung. The composite bacteria comprises Bacillus subtilis and Lysinibacillus fusiformis.

[0007] Preferably, the particle size of the sponge iron is 3 to 5 cm, Fe 0 The content is ≥85%, the pore size is 50-200μm, and the porosity is 60%-80%.

[0008] Preferably, the bacterial concentration of the composite bacteria is 1×10 7 ~1×10 9 CFU / mL.

[0009] Preferably, the preparation method of the composite bacteria is: culturing Bacillus subtilis and Lysinibacillus to the logarithmic growth phase respectively, and mixing the logarithmic growth phase culture fluid of Bacillus subtilis and the logarithmic growth phase culture fluid of Lysinibacillus spindle-shaped in a volume ratio of (1:1) to (3:2).

[0010] The present invention also provides a method for aerobic composting of cow dung, comprising the following steps: mixing cow dung and a plant-based expander to obtain a compost matrix; and mixing the compost matrix with the sponge iron and composite bacteria in the application to perform aerobic composting.

[0011] Preferably, the plant-based expander includes straw; the straw includes rice straw.

[0012] Preferably, the mass ratio of the compost matrix to the sponge iron is 100:6-9.

[0013] Preferably, the mass volume ratio of the compost substrate to the composite bacteria is 100kg:5-10L.

[0014] Preferably, the C / N ratio of the composting matrix is ​​25-30:1; and before aerobic composting, the moisture content of the mixture is adjusted to 55%-65%.

[0015] Preferably, during aerobic composting, the ventilation rate is 0.5 to 1.0 L min -1 kg -1 , stir once every 2 to 3 days, each time for 20 to 30 minutes.

[0016] Beneficial effects of the present invention:

[0017] The present invention adds sponge iron and composite bacteria to aerobic composting of cow dung, which has the following advantages:

[0018] First, it can increase compost temperature: composting materials enter a high-temperature phase (>50°C) within 3-5 days, and the duration of this phase is extended to 8-10 days, significantly higher than the control group (5 days). The peak compost temperature reaches 60.13°C, 5.06°C higher than the control group.

[0019] Second, it can promote the degradation of organic matter: it significantly improves the degradation rate of total organic matter (TOC).

[0020] Third, it can improve the humification degree of compost: it significantly increases the content of humic acid (HA) in the compost, and can promote the conversion of fulvic acid (FA) into humic acid, thereby improving the humification degree of the compost.

[0021] Fourth, it can optimize the structure of microbial communities: it significantly improved the diversity and richness of bacterial communities during the composting process, with the Shannon index and Chao 1 index significantly higher than those of the control group, and promoted the growth of key bacterial groups such as Firmicutes and Proteobacteria, which play an important role in compost humification and organic matter degradation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The appearance of the sponge iron of the present invention;

[0023] Figure 2 The changes in the contents of organic matter, cellulose, hemicellulose, and lignin before and after 30 days of cow dung composting, where D0 is the initial sample, CK is the comparative example 1 group, and SI is the example 1 group;

[0024] Figure 3 Figure 2 shows the changes in temperature, humus content, seed germination index, and carbon-nitrogen ratio during the composting process of cow dung in the sponge iron treatment group and the control group. A represents the temperature change, B represents the humus content, C represents the humic acid content, D represents the fulvic acid content, and E represents the carbon-nitrogen ratio and seed germination index.

[0025] Figure 4 The figures show the diversity changes and community succession of bacterial community structure at different periods of cow dung composting in the sponge iron treatment group and the control group, where A is the Shannon index, B is the Chao 1 index, C is the bacterial community structure at the phylum level, and D is the bacterial community structure at the genus level. CKd3, CKd7, CKd14, and CKd30 are the sampling results of the comparative example 1 group on the 3rd, 7th, 14th, and 30th days, respectively; SId3, SId7, SId14, and SId30 are the sampling results of the example 1 group on the 3rd, 7th, 14th, and 30th days, respectively; and d0 is the sampling result on day 0. DETAILED DESCRIPTION

[0026] The invention provides application of sponge iron synergistic composite bacteria in aerobic composting of cow dung. The composite bacteria comprises Bacillus subtilis and Lysinibacillus fusiformis.

[0027] In the present invention, the particle size of the sponge iron is preferably 3 to 5 cm, more preferably 3.5 to 4.5 cm; the Fe 0 The content is preferably ≥85%; the pore size of the sponge iron is preferably 50-200 μm, more preferably 100-150 μm; the porosity of the sponge iron is preferably 60%-80%, more preferably 65%-75%. The present invention has no special restrictions on the specific source of sponge iron. In some embodiments of the present invention, sponge iron is purchased from Henan Weikoteli Environmental Protection Technology Co., Ltd. The appearance of the sponge iron of the present invention is as follows Figure 1 In the present invention, the bacterial concentration of the composite bacteria is preferably 1×10 7 ~1×10 9 CFU / mL, more preferably 5×10 7 ~6×10 8 CFU / mL, more preferably 1×10 8 ~3×10 8CFU / mL. In the present invention, the preparation method of the composite bacteria is preferably: Bacillus subtilis and spindle-shaped Lysinibacillus are cultured to the logarithmic growth phase respectively, and the logarithmic growth phase culture solution of Bacillus subtilis and the logarithmic growth phase culture solution of Lysinibacillus spindle-shaped are mixed in a volume ratio of (1:1) to (3:2). In the present invention, the Bacillus subtilis is preferably Bacillus subtilis with a preservation number of CICC24634, and the spindle-shaped Lysinibacillus is preferably Lysinibacillus fusiformis with a preservation number of CICC 22657. In the present invention, the culture medium for culturing the two strains of bacteria to the logarithmic growth phase is preferably LB culture medium. During the culture, the initial inoculation is preferably inoculated with 1×10 7 ~1×10 9 CFU of Bacillus subtilis, 1×10 per 100 mL of LB medium 7 ~1×10 9 CFU of Lysinibacillus spindle-shaped. The present invention does not particularly limit the specific culture conditions, and conventional culture conditions in the art can be used. In some embodiments of the present invention, the volume ratio of the culture medium of Bacillus subtilis in the logarithmic growth phase to the culture medium of Lysinibacillus spindle-shaped is 1:1, 2:1, 1:2, 3:1 or 3:2.

[0028] The present invention adds sponge iron to the cow dung compost on the basis of adding composite bacteria, thereby further improving the activity and relative abundance of the composite bacteria, thereby improving the humification degree of the cow dung compost. Moreover, sponge iron, as an electron donor, promotes the synthesis of key enzymes and the release of biodegradable substances, and accelerates the degradation of organic matter. The present invention adds sponge iron and composite bacteria to the composting system, which can effectively enhance the composting process, and significantly improves the process efficiency and product quality of aerobic composting of cow dung by regulating the physical structure or chemical activity of the composting system. The sponge iron added by the present invention is a zero-valent iron material, which not only has the function of an electron donor, but also provides Fe 2+ / Fe 3+ It participates in the synthesis of certain key enzymes in the respiratory chain, and at the same time has a large porosity and specific surface area, and has good adsorption properties, which is beneficial to promoting microbial metabolic activity and accelerating the degradation of organic matter.

[0029] The present invention also provides a method for aerobic composting of cow dung, comprising the following steps: mixing cow dung and a plant-based expander to obtain a compost matrix; and mixing the compost matrix with the sponge iron and composite bacteria in the application to perform aerobic composting.

[0030] In the method of the present invention, the cow dung is preferably air-dried and crushed cow dung; the plant-based expander preferably includes straw; and the straw preferably includes rice straw. The present invention does not specifically limit the specific source of rice straw. In the present invention, the rice straw is preferably crushed, and the crushed length is preferably 1 to 3 cm, more preferably 1.5 to 2.5 cm. In the present invention, the mass ratio of compost substrate to sponge iron is preferably 100:6 to 9, and in some embodiments, it can be 100:6, 100:7, 100:8 or 100:9. In the present invention, the mass-to-volume ratio of compost substrate to composite bacteria is preferably 100 kg:5 to 10 L, and in some embodiments, it can be 100 kg:5 L, 100 kg:6 L, 100 kg:7 L, 100 kg:8 L, 100 kg:9 L or 100 kg:10 L. In the present invention, the C / N ratio of the composting matrix is ​​preferably 25 to 30:1. In some embodiments, it can be 25:1, 26:1, 27:1, 28:1, 29:1 or 30:1. Before aerobic composting, the water content of the mixture is preferably adjusted to 55%-65%. The solvent added when adjusting the water content is preferably water. In some embodiments, the water content of the mixture can be adjusted to 55%, 58%, 60% or 65%. In the present invention, when aerobic composting is performed, the ventilation rate is preferably 0.5 to 1.0 L min. -1 kg -1 , stirring once every 2 to 3 days, each time for 20 to 30 minutes; in some embodiments, the stirring time each time may be 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes or 30 minutes.

[0031] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0032] In the following examples, unless otherwise specified, all methods are conventional.

[0033] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0034] The sponge iron used in the following examples was purchased from Henan Weikoteli Environmental Protection Technology Co., Ltd.; the cow dung used in the following examples was collected from a farm in Dafu Town, Anhua County, Yiyang City, Hunan Province, and air-dried and shredded. Rice straw was also obtained from a local farm and shredded to lengths of 1-3 cm. The basic physical and chemical parameters of the air-dried and shredded cow dung and shredded rice straw in the following examples are shown in Table 1.

[0035] Table 1 Basic physical and chemical parameters of compost materials

[0036]

[0037] The solid-state fermentation reactor in the following examples is a double-layer vacuum-evacuated 304 stainless steel fermenter with an inner diameter of 300 mm, a height of 800 mm, and a volume of 50 L. Three stainless steel stirring paddles are installed in the reactor for turning the compost. Three sampling ports are distributed from top to bottom on the front, and three temperature sensors are vertically distributed on the back for real-time temperature recording. The bottom of the fermenter is a porous, breathable baffle with an air inlet and a leachate discharge port located below. The air inlet is connected to a gas rotor flowmeter and a vortex air pump, and aeration can be set to implement forced ventilation.

[0038] Example 1

[0039] A method for aerobic composting of cow dung, comprising the following steps:

[0040] 5 kg of cow dung and 2.69 kg of rice straw were mixed evenly with an initial carbon-nitrogen ratio (C / N) of 25:1 to obtain a compost matrix. Composite bacteria and sponge iron (the particle size of the sponge iron was 3 cm, Fe 0 The mixture was prepared by mixing the compost matrix with the composite bacteria in a mass volume ratio of 100 kg:5 L and the mass volume ratio of the compost matrix to the sponge iron in a mass ratio of 100:6. The water content of the mixture was adjusted to 60% and the mixture was placed in a solid-state fermentation reactor for aerobic composting. During the composting process, the ventilation rate was maintained at 0.5 L min. -1 kg -1 , stirring once every 2 days, each time for 20 minutes.

[0041] The preparation method of the composite bacteria is as follows: glycerol-preserved Bacillus subtilis (preservation number CICC 24634) is inoculated at a rate of 1×10 7 The amount of CFU was inoculated into LB medium and cultured to the logarithmic growth phase to obtain the logarithmic growth phase culture solution of Bacillus subtilis; Lysinibacillus fusiformis (deposit number CICC 22657) was inoculated at a rate of 1×10 per 100 mL of LB medium. 7 The amount of CFU was inoculated into LB medium and cultured to the logarithmic growth phase to obtain the logarithmic growth phase culture fluid of spindle-shaped Lysinibacillus; the logarithmic growth phase culture fluid of Bacillus subtilis and the logarithmic growth phase culture fluid of spindle-shaped Lysinibacillus were mixed in a volume ratio of 1:1 to obtain a bacterial concentration of 1×10 9 CFU / mL of composite bacteria.

[0042] Example 2

[0043] A method for aerobic composting of cow dung, comprising the following steps:

[0044] Cow dung and rice straw were mixed to adjust the initial carbon-nitrogen ratio (C / N) to 30:1 to obtain a compost matrix; composite bacteria and sponge iron (the particle size of the sponge iron was 5 cm, Fe 0 The mixture was prepared by adjusting the mass volume ratio of the compost matrix to the composite bacteria to be 100 kg:10 L, the mass volume ratio of the compost matrix to the sponge iron to be 100:9, and the water content of the mixture to be 65%. The mixture was placed in a solid-state fermentation reactor for aerobic composting. During the composting process, the ventilation rate was maintained at 1.0 L min. -1 kg -1 , stirring once every 3 days, each time stirring for 30 minutes.

[0045] The preparation method of the composite bacteria is as follows: glycerol-preserved Bacillus subtilis (preservation number CICC 24634) is inoculated at a rate of 1×10 8 The amount of CFU was inoculated into LB medium and cultured to the logarithmic growth phase to obtain the logarithmic growth phase culture solution of Bacillus subtilis; Lysinibacillus fusiformis (deposit number CICC 22657) was inoculated at a rate of 1×10 per 100 mL of LB medium. 8 The amount of CFU was inoculated into LB medium and cultured to the logarithmic growth phase to obtain the logarithmic growth phase culture fluid of spindle-shaped Lysinibacillus; the logarithmic growth phase culture fluid of Bacillus subtilis and the logarithmic growth phase culture fluid of spindle-shaped Lysinibacillus were mixed in a volume ratio of 3:2 to obtain a bacterial concentration of 1×10 8 CFU / mL of composite bacteria.

[0046] Example 3

[0047] A method for aerobic composting of cow dung, comprising the following steps:

[0048] Cow dung and rice straw were mixed to adjust the initial carbon-nitrogen ratio (C / N) to 28:1 to obtain a compost matrix; composite bacteria and sponge iron (the particle size of the sponge iron was 4 cm, Fe 0 The mixture was prepared by mixing the compost matrix with the composite bacteria in a mass volume ratio of 100 kg:7 L and the mass volume ratio of the compost matrix to the sponge iron in a mass ratio of 100:8. The water content of the mixture was adjusted to 55%. The mixture was placed in a solid-state fermentation reactor for aerobic composting. During the composting process, the ventilation rate was maintained at 0.8 L min. -1 kg -1 , stirring once every 2 days, each time stirring for 25 minutes.

[0049] The preparation method of the composite bacteria is as follows: glycerol-preserved Bacillus subtilis (preservation number CICC 24634) is inoculated at a rate of 1×10 9 The amount of CFU was inoculated into LB medium and cultured to the logarithmic growth phase to obtain the logarithmic growth phase culture solution of Bacillus subtilis; Lysinibacillus fusiformis (deposit number CICC 22657) was inoculated at a rate of 1×10 per 100 mL of LB medium. 9 The amount of CFU was inoculated into LB medium and cultured to the logarithmic growth phase to obtain the logarithmic growth phase culture fluid of spindle-shaped Lysinibacillus; the logarithmic growth phase culture fluid of Bacillus subtilis and the logarithmic growth phase culture fluid of spindle-shaped Lysinibacillus were mixed in a volume ratio of 2:1 to obtain a bacterial concentration of 1×10 8 CFU / mL of composite bacteria.

[0050] Comparative Example 1

[0051] The difference from Example 1 is that no sponge iron is added, and the rest is the same as Example 1.

[0052] Example 4

[0053] Detection of mineralization in Example 1 and Comparative Example 1

[0054] The composting end point was defined as the temperature dropping to room temperature. In Example 1, the composting time was 30 days. Samples were taken from the initial sample (marked as group D0) and the compost at the end point of the composting (the compost obtained in Example 1 (marked as group SI) and the compost obtained in Comparative Example 1 (marked as group CK)). Each sample was sampled at three sampling ports and mixed evenly.

[0055] The muffle furnace ignition method was used to determine the organic matter content of the samples, and the Van Soest method was used to determine the contents of cellulose, hemicellulose, and lignin in the samples, respectively.

[0056] The results are as follows Figure 2 As shown in the figure, the organic matter content in the pile can be used as an important indicator to judge the smooth progress of composting. During the composting process, the organic matter content shows a continuous dynamic attenuation trend. This process is mainly due to the conversion of organic matter into CO2, H2O and mineral forms (such as carbonates, etc.) through microbial metabolism. Figure 2 It can be seen that after calculation, compared with the D0 group, the final organic matter degradation rates of the CK and SI treatment groups (organic matter degradation rate = (D0-CK) / D0)×100% or (D0-SI) / D0)×100%) were 20.21% and 32.07%, respectively, indicating that the addition of sponge iron significantly promoted the degradation of organic matter in the composting system.

[0057] As the main component of cow dung and rice straw, the decomposition rate of lignocellulose directly affects the maturity of compost and the fertilizer efficiency of the product. Figure 2 It can be seen that at the end of composting, the cellulose content of the CK and SI groups was calculated to be 22.22% and 30.56% lower than that of the D0 group, respectively (the cellulose content reduction was calculated as (D0-CK) / D0) × 100% or (D0-SI) / D0) × 100%). The cellulose content in both composting treatments was significantly reduced, which was related to the inoculation of the composite bacteria. The addition of sponge iron further increased its degradation rate. This is because sponge iron creates a good living environment for the relevant microorganisms in the composting system and increases their metabolic activity. At the end of composting, compared with the D0 group, the hemicellulose degradation rate of the SI group (hemicellulose degradation rate = (D0-CK) / D0) × 100% or (D0-SI) / D0) × 100%) was 54.62%, significantly higher than the 40.34% of the CK group.

[0058] The lignin content in cow dung is much higher than that of cellulose and hemicellulose. Phenolic monomers, one of the products of lignin decomposition, are important precursors to quinone groups in the synthesis of humus, making them a key factor limiting the maturity of cow dung compost. At the end of composting, the lignin degradation rates of the CK and SI groups (lignin degradation rate = (DO - CK) / DO) × 100% or (DO - SI) / DO) × 100%) were 5.77% and 18.14%, respectively, compared to the DO group. The SI group showed a significantly greater decrease in lignin content than the CK group, suggesting that the porous structure, ion exchange properties, and adsorption of sponge iron enhance the activity of lignocellulose-degrading bacteria, thereby accelerating the degradation of lignocellulose components.

[0059] Example 5

[0060] Detection of humification in Example 1 and Comparative Example 1

[0061] The temperature of each day during the composting process of Example 1 (SI group) and Comparative Example 1 (CK group) was recorded respectively, and the composting end point was taken as the temperature gradually decreasing to room temperature (the composting cycle of Example 1 was 30 days). Samples were taken at three sampling ports on days 0, 3, 7, 14, 21, and 30, and mixed uniformly. Humic substances, humic acid, and fulvic acid solutions of the compost samples were extracted and separated, and the contents were determined using a TOC analyzer. The total organic carbon and total nitrogen contents of the samples were determined using combustion oxidation-non-dispersive infrared absorption method and Kjeldahl nitrogen determination method, and the ratio of their contents was used as C / N.

[0062] Take 5g of fresh sample from the 30th day and mix it with distilled water at a ratio of 1:10 (w / v). Shake at 25°C and 180rpm for 30 minutes, then let it stand and filter to prepare the extract. Evenly sow 10 soybean seeds of similar shape and size on a culture dish lined with filter paper, then add 15mL of extract so that the liquid covers the seeds. Distilled water is used as a control. Finally, place the culture dish in a 28°C incubator in the dark and culture. After 72 hours, measure the length of the germinated roots and record the germination rate. Calculate using the following formula:

[0063] Seed germination index (%) = (germination rate of seeds in the treatment group × average root length of seeds in the treatment group) / (germination rate of seeds in the control group × average root length of seeds in the control group) × 100%.

[0064] The results are as follows Figure 3 As shown. Figure 3 As shown in Figure 1, the SI treatment group exhibited a rapid temperature rise during the initial stages of composting (days 0-5). The SI group entered a high-temperature period (≥50°C) on day 5, reaching its highest temperature (60.13°C) on day 7, and the high-temperature period lasted for 9 days. In comparison, the high-temperature period in the CK group began on day 6 and lasted only 5 days. Furthermore, the peak temperature in the SI treatment group increased by 5.06°C compared to the CK group. After 30 days of aerobic composting, the temperature gradually dropped to room temperature, essentially marking the end of composting. This suggests that sponge iron enhances microbial activity in the composting system, promoting the decomposition of substances and releasing more heat, thereby increasing the compost temperature, prolonging the high-temperature period, and effectively shortening the composting cycle compared to traditional composting.

[0065] Humus is an important component of compost products, and its formation is mainly controlled by the mineralization and humification process of organic matter. Figure 3 As can be seen from Figure B, the SI treatment group had a significant increase, which may be due to the fact that its higher pile temperature and good ventilation environment stimulated the activity of certain thermophilic aerobic microorganisms, which was beneficial to improve their lignocellulase activity and promoted the conversion of lignin and some crude protein into humus precursors, thereby forming humus (HS) faster. With the consumption of easily degradable organic matter, part of the humus was gradually consumed and utilized by microorganisms as a carbon source, resulting in a gradual decrease in the humus content. The humus content of the SI and CK groups increased from an initial 124.46 g·kg -1 The final change was 130.56 g·kg -1 and 120.36 g·kg -1 The results showed that sponge iron promoted the formation and accumulation of humus in cow dung compost.

[0066] Humic acid and fulvic acid are the main components of humus, and they can be dynamically transformed through molecular recombination. Fulvic acid has more acidic functional groups and a lower molecular weight, so its water solubility is significantly higher than that of humic acid. The molecular structure of humic acid (HA) is more complex and stable. In contrast to the decreasing trend of fulvic acid, the content of humic acid shows a fluctuating upward trend throughout the composting process ( Figure 3 The final humic acid content in the SI treatment group was higher than that in the CK group (67.22 g·kg -1 ) increased by 38.08%. It can be speculated that during the humification process, fulvic acid undergoes molecular reconstruction through decarboxylation and condensation reactions, transforming into humic acid. The final humic acid content in the SI-treated group was higher than that in the CK-treated group, indicating that the addition of sponge iron promotes the synthesis and accumulation of humic acid in cow dung compost, resulting in a more stable and highly humified compost product in the SI-treated group.

[0067] like Figure 3 As shown in D, the fulvic acid content in the initial stage of composting increased in stages and then continued to decrease. By the end of composting, the FA content in the SI and CK treatment groups decreased from the initial value of 67.87 g·kg -1 Reduced to 30.18 g·kg -1 and 45.73 g·kg -1 , indicating that the addition of sponge iron promoted the decomposition and utilization of fulvic acid by microorganisms in the cow dung composting system, as well as the conversion of fulvic acid to the more stable humic acid through re-condensation and polymerization.

[0068] The carbon-nitrogen ratio (C / N) is a commonly used indicator for evaluating compost stabilization and maturity. Its dynamic changes directly reflect the organic matter transformation process. Generally, when the C / N ratio drops below 20:1, it is used as the evaluation standard for the basic maturity of the compost. Figure 3 It can be seen from E in that both Example 1 and Comparative Example 1 have reached this standard. However, it may not be reasonable to simply rely on the final value of C / N as an evaluation index for compost maturity, so the ratio of the initial and final C / N ratios of the compost sample (T value) is further used to characterize its degree of maturity. Generally, when T<0.6, the compost is judged to have reached a mature state. The T value of the SI treatment group in the present invention is 0.43, while the CK group does not meet the standard, indicating that the addition of sponge iron improves the degree of maturity of cow dung compost. It is used to characterize the phytotoxicity of compost products and is also one of the core indicators for compost maturity assessment. After 30 days of composting, the final seed germination indexes of the CK and SI groups were 81.94% and 98.50%, respectively, both exceeding 80%, indicating that the compost products have reached the maturity standard and there is no phytotoxicity hazard. And the SI treatment has better humification and harmlessness effects on the compost.

[0069] Example 6

[0070] Detection of bacterial community structure in Example 1 and Comparative Example 1

[0071] The temperature of each day during the composting process of Example 1 (SI group) and Comparative Example 1 (CK group) was recorded, and the composting end point was when the temperature gradually dropped to room temperature (the composting period of Example 1 was 30 days). Samples were taken from three sampling ports on days 0, 3, 7, 14, and 30, and mixed evenly. DNA extraction and high-throughput sequencing were performed, representing the initial stage (0 day), warming stage (3 days), thermophilic stage (7 days), cooling stage (14 days), and mature stage (30 days) of the compost, respectively. The two treatment groups had the same day 0 sample. Genomic DNA from each compost sample was extracted using the DNeasy PowerSoil kit (QIAGEN, Dusseldorf, Germany) according to the operating instructions, and the integrity of the extracted DNA was subsequently tested and verified by 1% agarose gel electrophoresis.

[0072] The V3-V4 hypervariable region of the bacterial 16S rRNA gene was amplified by PCR using primer pair 341F (5'-CCTACGGGNGGCWGCAG-3' (SEQ ID NO. 1)) and 805R (5'-GACTACHVGGGTATCTAATCC-3' (SEQ ID NO. 2)). The quality of the PCR product was again checked by 1% agarose gel electrophoresis. Subsequently, high-throughput sequencing of the 16S rRNA gene was performed on an Illumina NovaSeq PE250 platform at LC-Bio Technology Co., Ltd. (Hangzhou, China).

[0073] The results are as follows Figure 4 As shown in the figure, generally speaking, higher Shannon index and Chao 1 index represent higher community diversity and richness. Figure 4 A and B in the figure reflect the changes in the diversity of bacterial communities during the composting process of the two groups of cow dung. In the present invention, the addition of sponge iron can effectively improve the diversity and richness of the microbial community, which is specifically manifested in that the Shannon index and Chao 1 index of the SI treatment are higher than those of the CK group in each stage of composting. This may be attributed to the porous structure of sponge iron providing a favorable space for bacterial growth and reproduction, and it provides the necessary iron elements for bacterial respiration and metabolism. In addition, the Shannon index of each treatment group decreased during the high temperature period, which may be because the high temperature environment inhibited the activity of most microorganisms, and only heat-resistant bacteria survived. Based on the above results, the intervention of sponge iron can promote the construction of microbial communities and improve the diversity and balance of cow dung compost bacterial communities.

[0074] Figure 4Figure C shows the relative abundance of dominant bacterial communities at the phylum level during each stage of cow manure composting. In the initial stage, Proteobacteria, Bacteroidota, and Actinobacteriota were the predominant bacterial communities. Once the compost entered the high-temperature stage, Firmicutes and Actinobacteriota became the dominant phyla. Firmicutes are able to adapt to high temperatures and produce extracellular enzymes such as spores, proteases, lipases, and cellulases, while Actinobacteriota can induce other microorganisms to secrete lignocellulose-degrading enzymes, promoting lignocellulose decomposition. The relative abundances of Firmicutes and Actinobacteriota were higher in the SI treatment than in the CK treatment, indicating that the additive treatment promoted the breakdown of macromolecular proteins, starch, and lignocellulose components within the composting system, which is also related to the increased humification level in the SI treatment. As the compost temperature gradually decreased, Proteobacteria began to dominate. By the mature stage, the relative abundance of Proteobacteria in the SI treatment reached 50.54%, significantly higher than the 30.19% in the CK treatment. The above results indicate that the application of sponge iron can effectively optimize the bacterial community structure of cow dung compost and create a more favorable microbial environment for the composting process.

[0075] Figure 4 D in the figure shows the relative abundance distribution characteristics of dominant bacteria at the genus level. After entering the warming stage, the abundance of soil Bacillus and Bacillus in each treatment group increased significantly, while the relative abundance of Psychrobacter decreased significantly. The dominant genera in the high-temperature composting system are Solibacillus, Bacillus and Lysinibacillus, of which the total proportion of the three in the SI treatment is more than 50%. As common groups under the Firmicutes phylum, these genera have the characteristics of producing high-temperature and high-osmotic-pressure-resistant spores and a variety of degradative enzymes, and can directly participate in the formation of humus and humus precursors. These characteristics are closely related to the maturity of the compost. As the temperature decreases and the organic component decreases, the relative abundance of Bacillus decreases significantly, while the relative abundance of Pseudomonas increases significantly. The relative abundance of Pseudomonas in the SI group increases significantly when entering the cooling period. Pseudomonas is a genus under the Proteobacteria phylum with nitrogen-fixing properties. Its relative abundance in the mature stage reached 29.20% in the SI treatment, which was significantly higher than that in the CK treatment (15.63%). This also indicates the positive effect of sponge iron on nitrogen retention in cow dung compost.

[0076] 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 principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. Application of sponge iron synergistic composite bacteria in aerobic composting of cow dung, characterized in that: The composite bacteria include Bacillus subtilis and Lysinibacillus spindle-shaped.

2. The use according to claim 1, characterized in that The particle size of the sponge iron is 3 to 5 cm, Fe 0 The content is ≥85%, the pore size is 50-200μm, and the porosity is 60%-80%.

3. The use according to claim 1, characterized in that The bacterial concentration of the composite bacteria is 1×10 7 ~1×10 9 CFU / mL.

4. The use according to claim 1, characterized in that The preparation method of the composite bacteria comprises the following steps: culturing Bacillus subtilis and Lysinibacillus to the logarithmic growth phase respectively, and mixing the logarithmic growth phase culture fluid of Bacillus subtilis and the logarithmic growth phase culture fluid of Lysinibacillus spindle-shaped in a volume ratio of (1:1) to (3:2).

5. A method for aerobic composting of cow dung, characterized in that: The method comprises the following steps: mixing cow dung and a plant bulking agent to obtain a compost matrix; and mixing the compost matrix with the sponge iron and composite bacteria in any one of claims 1 to 4 to perform aerobic composting.

6. The method according to claim 5, characterized in that The plant-based expander includes straw; the straw includes rice straw.

7. The method according to claim 5, characterized in that The mass ratio of compost matrix to sponge iron is 100:6-9.

8. The method according to claim 5, characterized in that The mass volume ratio of compost matrix and composite bacteria is 100kg:5~10L.

9. The method according to claim 5, characterized in that The C / N ratio of the composting matrix is ​​25-30:1; before aerobic composting, the moisture content of the mixture is adjusted to 55%-65%.

10. The method according to claim 5, characterized in that When aerobic composting is carried out, the ventilation rate is 0.5-1.0 L·min -1 kg -1 , stir once every 2 to 3 days, each time for 20 to 30 minutes.

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