High-efficiency low-pollution cow dung returning treatment method

Abstract

The invention provides a high-efficiency low-pollution cow dung returning treatment method, which comprises the following steps: adding corn straw and charcoal into cow dung, preparing a fermentation base material, inoculating a compound fermentation inoculant, and carrying out composting fermentation to prepare a cow dung organic fertilizer. The composite microbial inoculant adopts an inner and outer double-film coating structure, aerobic bacteria are embedded in the middle, are released in the early stage of composting, quickly enter a high-temperature stage and decompose and metabolize organic matters, anaerobic bacteria are embedded in the innermost layer, and an inner film coating material adopts composite modified waterborne polyurethane, so that the composite microbial inoculant has a good anti-bacterial effect. Azobenzene and waxberry tannin combined modification endows the membrane structure with the characteristics of low-oxygen cracking, normal-oxygen stability and no influence of enzyme, anaerobic bacteria are released under the low-oxygen condition in the high-temperature last stage and the decomposition period, decomposition of residual cellulose can be promoted, carbon and nitrogen loss caused in anaerobic fermentation is prevented, the speed of converting organic matter into humus is increased, and the yield of the organic matter is increased. Meanwhile, the inner film packing material reacts with the organic acid and the ethanol, so that the quality of the cow dung organic fertilizer is further ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of organic fertilizer processing, and in particular relates to a high-efficiency and low-pollution method for returning cow dung to fields. Background Art

[0002] With the continuous adjustment of my country's agricultural industrial model, my country's animal husbandry and poultry farming industry has developed rapidly, tending towards intensive and large-scale directions. The manure produced by livestock and poultry animals has caused tremendous pressure on the farms, and at the same time brought more serious problems to the environment, such as environmental pollution and eutrophication of soil and groundwater. Therefore, scientifically and effectively treating manure for fertilizer return can not only solve the environmental pollution problem of manure and realize the high-value utilization of waste, but also promote the sustainable and stable development of animal husbandry and poultry farming industry. Cattle breeding is an important component of the livestock breeding industry, and cow dung is the main pollutant in the cattle breeding process. Since cow dung contains a large amount of nitrogen and phosphorus compounds, if it enters the soil directly without treatment, it will be converted into nitrates and phosphates. Excessive content causes the soil to lose its production value, thereby causing eutrophication of surface water and groundwater, and further endangering the stable development of other related industries. The existing method of treating cow dung is mainly to return it to the field, among which composting fermentation is the main method of returning it to the field, and the organic matter and nutrients in the cow dung are degraded by the diversity of microorganisms to form organic fertilizers for soil fertilization. At present, composting fermentation is mainly achieved by adding exogenous biological fermentation agents, because traditional composting fermentation is based on the degradation of cow dung by the original microorganisms in cow dung. There are relatively few microorganisms that play a role in the initial stage of fermentation, resulting in an extension of the fermentation cycle and a large loss of nitrogen. At the same time, the fermentation cycle and conditions will affect the survival rate and reproduction of functional microorganisms, and the weed seeds and insect eggs contained in the cow dung are not completely eliminated, which leads to poor cow dung treatment effect, and the prepared fertilizer cannot meet the nutritional needs of crop growth. Existing composting fermentation can also be divided into aerobic fermentation and anaerobic fermentation, among which aerobic fermentation is the main fermentation method. Aerobic fermentation is under aerobic conditions, microorganisms degrade organic matter in cow dung and convert it into small molecules such as CO2 and ammonia and humus. Although it can accelerate the decomposition of the substrate in the initial stage of composting fermentation, quickly enter the maturity stage, speed up the maturity process, and shorten the composting cycle, it is mainly based on batch fermentation, with low fermentation efficiency, and each batch needs to add biological fermentation agents, which increases the fermentation cost and reduces the fermentation efficiency of microorganisms to a certain extent, thereby affecting the quality of organic fertilizer. At present, there are corresponding studies on the combined technology of aerobic fermentation and anaerobic fermentation in the research of cow dung composting fermentation. Based on the efficient fermentation ability of aerobic fermentation in the early stage of composting and the high temperature period, the organic matter can be quickly decomposed. The anaerobic fermentation accelerates the synthesis of humus in the late high temperature period and the mature stage, and further shortens the mature period. However, the existing alternating aerobic fermentation and anaerobic fermentation is mainly carried out by directly inoculating a mixture of aerobic and anaerobic bacteria into the cow dung fermentation base. This addition method will affect the survival of anaerobic bacteria under normoxic conditions in the early stage of composting, reduce the efficiency of anaerobic fermentation in the later stage, and thus have a bad effect on the quality of cow dung organic fertilizer. Therefore, there is an urgent need to provide an efficient and low-pollution method for returning cow dung to the fields, which can ensure that farmland can maximize the use of the nutrients in cow dung fertilizer and achieve certain agricultural benefits, while minimizing the pollution to the environment after discharge, and provide a reference for large-scale and industrialized return of cow dung to the fields. It can maximize the absorption of farm fecal waste while ensuring that both ecological benefits and certain economic benefits can be obtained, and provide a reference for the return of solid waste from large-scale and intensive farms to the fields. Summary of the invention

[0003] Technical problems to be solved: In view of the above technical problems, the purpose of the present invention is to provide a method for returning cow dung to the field with high efficiency and low pollution, and the steps are as follows: add corn stalks and biochar to cow dung, prepare a fermentation base material, and then inoculate a composite fermentation agent for composting and fermentation to obtain cow dung organic fertilizer. In the present invention, the composite bacterial agent adopts an inner and outer double-membrane coating structure, aerobic bacteria are embedded in the middle, released in the early stage of composting, quickly enter the high temperature period and decompose organic matter, and anaerobic bacteria are embedded in the innermost layer, the inner membrane packaging material adopts a composite modified polyurethane, and azophenyl and bayberry tannin are jointly modified to give the membrane structure the characteristics of being able to lyse in low oxygen, stable in normal oxygen, and not affected by enzymes, so that anaerobic bacteria are released under low oxygen conditions at the end of high temperature and during the decomposition period, which can promote the decomposition of residual cellulose, prevent the loss of carbon and nitrogen caused by anaerobic fermentation, accelerate the speed of converting organic matter into humus, shorten the fermentation cycle of cow dung composting, and at the same time, the inner membrane packaging material reacts with organic acids and ethanol to further ensure the quality of cow dung organic fertilizer.

[0004] Technical solution: A highly efficient and low-pollution method for returning cow dung to the field, comprising the following steps: S1. The corn stalks and biochar were mixed evenly with cow dung, the carbon-nitrogen ratio was adjusted to (20-30): 1, and then water was added to adjust the moisture content to 50-65% to obtain a cow dung fermentation base; S2. Add the composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The composite fermentation bacterial agent is composed of aerobic bacteria and anaerobic bacteria, wherein the aerobic bacteria are composed of actinomycetes, bacillus subtilis, nitrogen-fixing bacteria and yeast, and the anaerobic bacteria are composed of clostridium cellulolyticum, clostridium pasteurianum, clostridium ljungdahlii and sulfur-oxidizing bacteria. Furthermore, in step S1, the ratio of corn straw to cow dung is (3-1):(1-2), and the amount of biochar added is 5-15%, based on the total weight of corn straw and cow dung. Furthermore, the inoculation amount of the composite fermentation agent in step S2 is 1-5%. Furthermore, the method for preparing the composite fermentation agent in step S2 comprises the following steps: Step 1. preparing an anaerobic bacterial suspension and a modified aqueous polyurethane membrane liquid, and adding the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to obtain anaerobic bacterial suspension microspheres; Step 2. Prepare aerobic bacterial suspension and chitosan solution, mix the anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise into the chitosan solution, perform vacuum concentration and freeze drying, and obtain the composite fermentation agent. Furthermore, the preparation method of the modified waterborne polyurethane in step 1 is to firstly mix the waterborne polyurethane and 4,4'-dihydroxyazobenzene in a mass ratio of 1:(2-4), stir at 60°C until completely dissolved, then add 10-20% bayberry tannin, heat to 120-150°C and keep for 20-40 minutes, cool and dry to obtain the modified waterborne polyurethane. Furthermore, the anaerobic bacterial suspension in step 1 is composed of a suspension of Clostridium cellulolyticum, a suspension of Clostridium pasteurianum, a suspension of Clostridium ljungdahlii and a suspension of sulfur-oxidizing bacteria, and the ratio thereof is (1-3):(0.5-2):(1-2):(0.5-1.5), and the bacterial concentration thereof is (10-15)×10 8 CFU / mL. Furthermore, in step 1, the ratio of the anaerobic bacterial suspension to the modified aqueous polyurethane membrane liquid is 1:(2-5). Furthermore, in step 2, the aerobic bacterial suspension is composed of an actinomycete suspension, a Bacillus subtilis suspension, a nitrogen-fixing bacteria suspension and a yeast suspension in a ratio of (1-4):(1-3):(0.5-1.5):(1-3), and the bacterial concentration is (5-15)×1010 CFU / mL. Furthermore, in step 2, the ratio of the anaerobic bacteria suspension microspheres, the aerobic bacteria suspension and the chitosan solution is (1-3):(2-4):(1-5). Beneficial effects: 1. The present invention adopts an inner and outer double-membrane coating structure to embed aerobic bacteria and anaerobic bacteria, and realizes phased release during the cow dung fermentation process. Aerobic bacteria decompose and metabolize organic matter such as cellulose and protein in cow dung under normoxic conditions in the early stage of composting and the high temperature period, fix carbon and nitrogen substances in cow dung to achieve the purpose of preventing loss, and aerobic bacteria quickly decompose organic matter to release heat, so that the temperature inside the pile body rises rapidly, shortens the time node of the high temperature period, and prolongs the maintenance time of the high temperature period, thereby eliminating harmful bacteria and insect eggs in the cow dung to the greatest extent; anaerobic bacteria further decompose the remaining cellulose in the late high temperature period and the mature stage, promote the combination of low molecular weight substances into stable and complex humus, shorten the time of the mature stage, and thus shorten the entire fermentation cycle of cow dung fermentation. 2. In the present invention, azobenzene and bayberry tannin are used to modify the internal membrane material of the composite fermentation agent. Azobenzene itself has the characteristic of low-oxygen activation, which gives the modified waterborne polyurethane film the function of cleaving and releasing anaerobic bacteria under low-oxygen conditions. Under low-oxygen conditions, the azo group in the azobenzene group is broken by the reductase in cow dung, thereby degrading the modified waterborne polyurethane film. At the same time, bayberry tannin is further modified and attached to its exterior, giving the modified waterborne polyurethane the function of stable existence before aerobic fermentation of cow dung. Bayberry tannin contains multiple hydroxyl groups and aromatic rings, which cause it to polymerize to form polymer condensed tannins without exposing enzyme catalytic sites. In addition, the organic matter in the cow dung will first combine with the enzyme produced by aerobic microorganisms, further protecting the internal structure from being decomposed, thereby stably existing. 3. The anaerobic bacteria in the composite fermentation agent of the present invention adopt the synergistic effect of Clostridium cellulolyticum, Clostridium pasteurianum, Clostridium ljungdahlii and sulfur oxidizing bacteria. Clostridium cellulolyticum secretes cellulase to decompose the remaining cellulose in the mature stage, and promotes the rapid conversion of low molecular weight substances into humus during high temperature. Clostridium pasteurianum, Clostridium ljungdahlii and sulfur oxidizing bacteria respectively play the role of nitrogen fixation, carbon fixation and oxidation of hydrogen sulfide to generate bound sulfur, thereby reducing the carbon, nitrogen and sulfur gaseous substances produced by anaerobic fermentation in the mature stage to the greatest extent, avoiding the loss of carbon, nitrogen and sulfur in the cow dung organic fertilizer, and ensuring the good quality of the cow dung organic fertilizer. 4. The present invention utilizes aerobic bacteria and anaerobic bacteria to synergistically ferment and decompose organic matter in cow dung based on the phased release of bacterial strains, which can improve the fermentation efficiency of cow dung, shorten the cow dung composting fermentation cycle, and improve the quality of cow dung organic fertilizer. It not only provides research data for the large-scale, industrialized and intensive processing of cow dung organic fertilizer, but also provides a solid theoretical support and data basis for the research and development of new methods for returning cow dung to the fields. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1The temperature changes during the composting fermentation process of Example 11 and Comparative Examples 1-3; Figure 2 The total nitrogen, available phosphorus, available potassium, electrical conductivity and humus ratio of Example 11 and Comparative Examples 1-3. DETAILED DESCRIPTION The present invention will be further described below in conjunction with embodiments, which are explanations of the present invention and are not limited to the following embodiments: The strains used in the present invention: Clostridium cellulolyticum B89510, purchased from Ningbo Mingzhou Biotechnology Co., Ltd.; Clostridium pasteurianum CICC10391, purchased from China Industrial Microbiological Culture Collection Management Center; Clostridium young'sii HZB414856, purchased from Wuhan Huizao Biotechnology Co., Ltd.; sulfur-oxidizing bacteria JCM39442, purchased from Guangdong Microbiological Culture Collection Center; Actinomycetes CICC10650, Bacillus subtilis CICC24534, and Azotobacter nitrogen-fixing bacterium CICC21685; Candida krusei HZB189957, purchased from Wuhan Huizao Biotechnology Co., Ltd.; Example 1 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. Mix 30kg corn straw and 20kg cow dung, add 5kg biochar, adjust the carbon-nitrogen ratio to 25:1, and then add water to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 2.75kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 80 mL of anaerobic bacterial suspension (32 mL of Clostridium cellulolyticum suspension, 16 mL of Clostridium pasteurianum suspension, 16 mL of Clostridium youngdae suspension, and 16 mL of sulfur-oxidizing bacteria suspension) and 320 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to prepare anaerobic bacterial suspension microspheres; Step 2. Prepare 1200 mL of aerobic bacterial suspension (400 mL of actinomycete suspension, 200 mL of Bacillus subtilis suspension, 200 mL of nitrogen-fixing bacteria suspension, 400 mL of yeast suspension) and 1600 mL of chitosan solution, mix 400 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-dry to obtain a composite fermentation agent. Example 2 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn straw and 10kg cow dung were mixed evenly, and then 4kg biochar was added to adjust the carbon-nitrogen ratio to 23:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 2.2kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 80 mL of anaerobic bacterial suspension (32 mL of Clostridium cellulolyticum suspension, 16 mL of Clostridium pasteurianum suspension, 16 mL of Clostridium youngdae suspension, and 16 mL of sulfur-oxidizing bacteria suspension) and 320 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to prepare anaerobic bacterial suspension microspheres; Step 2. Prepare 1200 mL of aerobic bacterial suspension (400 mL of actinomycete suspension, 200 mL of Bacillus subtilis suspension, 200 mL of nitrogen-fixing bacteria suspension, 400 mL of yeast suspension) and 1600 mL of chitosan solution, mix 400 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-dry to obtain a composite fermentation agent. Example 3 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. Mix 20kg corn straw and 10kg cow dung, add 3kg biochar, adjust the carbon-nitrogen ratio to 22:1, and then add water to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 1.65kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 80 mL of anaerobic bacterial suspension (32 mL of Clostridium cellulolyticum suspension, 16 mL of Clostridium pasteurianum suspension, 16 mL of Clostridium youngdae suspension, and 16 mL of sulfur-oxidizing bacteria suspension) and 320 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to prepare anaerobic bacterial suspension microspheres; Step 2. Prepare 1200 mL of aerobic bacterial suspension (400 mL of actinomycete suspension, 200 mL of Bacillus subtilis suspension, 200 mL of nitrogen-fixing bacteria suspension, 400 mL of yeast suspension) and 1600 mL of chitosan solution, mix 400 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-dry to obtain a composite fermentation agent. Example 4 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn straw and 30kg cow dung were mixed evenly, and then 6kg biochar was added, the carbon-nitrogen ratio was adjusted to 24:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 3.3kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 100 mL of anaerobic bacterial suspension (40 mL of Clostridium cellulolyticum suspension, 20 mL of Clostridium pasteurianum suspension, 20 mL of Clostridium youngdae suspension, and 20 mL of sulfur-oxidizing bacteria suspension) and 400 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to obtain anaerobic bacterial suspension microspheres; Step 2. Prepare 1500mL aerobic bacterial suspension (500mL actinomycetes suspension, 250mL Bacillus subtilis suspension, 250mL nitrogen-fixing bacteria suspension, 500mL yeast suspension) and 2000mL chitosan solution, mix 500mL anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration and freeze-drying, and obtain a composite fermentation agent. Example 5 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. Mix 20kg corn straw and 40kg cow dung, add 6kg biochar, adjust the carbon-nitrogen ratio to 23:1, and then add water to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 3.3kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 100 mL of anaerobic bacterial suspension (40 mL of Clostridium cellulolyticum suspension, 20 mL of Clostridium pasteurianum suspension, 20 mL of Clostridium youngdae suspension, and 20 mL of sulfur-oxidizing bacteria suspension) and 400 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to obtain anaerobic bacterial suspension microspheres; Step 2. Prepare 1500mL aerobic bacterial suspension (500mL actinomycetes suspension, 250mL Bacillus subtilis suspension, 250mL nitrogen-fixing bacteria suspension, 500mL yeast suspension) and 2000mL chitosan solution, mix 500mL anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration and freeze-drying, and obtain a composite fermentation agent. Example 6 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn straw and 10kg cow dung were mixed evenly, and then 2kg biochar was added to adjust the carbon-nitrogen ratio to 23:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 2.1kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 80 mL of anaerobic bacterial suspension (32 mL of Clostridium cellulolyticum suspension, 16 mL of Clostridium pasteurianum suspension, 16 mL of Clostridium youngdae suspension, and 16 mL of sulfur-oxidizing bacteria suspension) and 320 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to prepare anaerobic bacterial suspension microspheres; Step 2. Prepare 1200 mL of aerobic bacterial suspension (400 mL of actinomycete suspension, 200 mL of Bacillus subtilis suspension, 200 mL of nitrogen-fixing bacteria suspension, 400 mL of yeast suspension) and 1600 mL of chitosan solution, mix 400 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-dry to obtain a composite fermentation agent. Example 7 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn stalks and 10kg cow dung were mixed evenly, and then 6kg biochar was added, the carbon-nitrogen ratio was adjusted to 24:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 2.3kg of composite fermentation agent to the cow dung fermentation base, mix well, place in a fermentation tank for fermentation, and obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 80 mL of anaerobic bacterial suspension (32 mL of Clostridium cellulolyticum suspension, 16 mL of Clostridium pasteurianum suspension, 16 mL of Clostridium youngdae suspension, and 16 mL of sulfur-oxidizing bacteria suspension) and 320 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to prepare anaerobic bacterial suspension microspheres; Step 2. Prepare 1200 mL of aerobic bacterial suspension (400 mL of actinomycete suspension, 200 mL of Bacillus subtilis suspension, 200 mL of nitrogen-fixing bacteria suspension, 400 mL of yeast suspension) and 1600 mL of chitosan solution, mix 400 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-dry to obtain a composite fermentation agent. Example 8 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn straw and 10kg cow dung were mixed evenly, and then 4kg biochar was added, the carbon-nitrogen ratio was adjusted to 23:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 0.44kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 80 mL of anaerobic bacterial suspension (32 mL of Clostridium cellulolyticum suspension, 16 mL of Clostridium pasteurianum suspension, 16 mL of Clostridium youngdae suspension, and 16 mL of sulfur-oxidizing bacteria suspension) and 320 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to prepare anaerobic bacterial suspension microspheres; Step 2. Prepare 1200 mL of aerobic bacterial suspension (400 mL of actinomycete suspension, 200 mL of Bacillus subtilis suspension, 200 mL of nitrogen-fixing bacteria suspension, 400 mL of yeast suspension) and 1600 mL of chitosan solution, mix 400 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-dry to obtain a composite fermentation agent. Example 9 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn straw and 10kg cow dung were mixed evenly, and then 4kg biochar was added to adjust the carbon-nitrogen ratio to 23:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 1.32kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 80 mL of anaerobic bacterial suspension (32 mL of Clostridium cellulolyticum suspension, 16 mL of Clostridium pasteurianum suspension, 16 mL of Clostridium youngdae suspension, and 16 mL of sulfur-oxidizing bacteria suspension) and 320 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to prepare anaerobic bacterial suspension microspheres; Step 2. Prepare 1200 mL of aerobic bacterial suspension (400 mL of actinomycete suspension, 200 mL of Bacillus subtilis suspension, 200 mL of nitrogen-fixing bacteria suspension, 400 mL of yeast suspension) and 1600 mL of chitosan solution, mix 400 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-dry to obtain a composite fermentation agent. Example 10 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn straw and 10kg cow dung were mixed evenly, and then 4kg biochar was added to adjust the carbon-nitrogen ratio to 23:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 2.2kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 100 mL of anaerobic bacterial suspension (40 mL of Clostridium cellulolyticum suspension, 20 mL of Clostridium pasteurianum suspension, 20 mL of Clostridium youngdae suspension, and 20 mL of sulfur-oxidizing bacteria suspension) and 200 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to obtain anaerobic bacterial suspension microspheres; Step 2. Prepare 900 mL of aerobic bacterial suspension (300 mL of actinomycete suspension, 150 mL of Bacillus subtilis suspension, 150 mL of nitrogen-fixing bacteria suspension, and 150 mL of yeast suspension) and 1200 mL of chitosan solution, mix 300 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, and then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-drying to obtain a composite fermentation agent. Embodiment 11 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn straw and 10kg cow dung were mixed evenly, and then 4kg biochar was added, the carbon-nitrogen ratio was adjusted to 23:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 2.2kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 90 mL of anaerobic bacterial suspension (15 mL of Clostridium cellulolyticum suspension, 30 mL of Clostridium pasteurianum suspension, 30 mL of Clostridium youngdae suspension, and 15 mL of sulfur-oxidizing bacteria suspension) and 360 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to obtain anaerobic bacterial suspension microspheres; Step 2. Prepare 1350 mL of aerobic bacterial suspension (400 mL of actinomycete suspension, 200 mL of Bacillus subtilis suspension, 200 mL of nitrogen-fixing bacteria suspension, 400 mL of yeast suspension) and 1800 mL of chitosan solution, mix 450 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-dry to obtain a composite fermentation agent. Example 12 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn straw and 10kg cow dung were mixed evenly, and then 4kg biochar was added, the carbon-nitrogen ratio was adjusted to 23:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 2.2kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 120 mL of anaerobic bacterial suspension (48 mL of Clostridium cellulolyticum suspension, 24 mL of Clostridium pasteurianum suspension, 24 mL of Clostridium youngdae suspension, and 24 mL of sulfur-oxidizing bacteria suspension) and 480 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to prepare anaerobic bacterial suspension microspheres; Step 2. Prepare 900 mL of aerobic bacterial suspension (300 mL of actinomycete suspension, 150 mL of Bacillus subtilis suspension, 150 mL of nitrogen-fixing bacteria suspension, 300 mL of yeast suspension) and 1500 mL of chitosan solution, mix 600 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-dry to obtain a composite fermentation agent. Example 13 A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn straw and 10kg cow dung were mixed evenly, and then 4kg biochar was added, the carbon-nitrogen ratio was adjusted to 23:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 2.2kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 56 mL of anaerobic bacterial suspension (22.4 mL of Clostridium cellulolyticum suspension, 11.2 mL of Clostridium pasteurianum suspension, 11.2 mL of Clostridium youngdae suspension, and 11.2 mL of sulfur-oxidizing bacteria suspension) and 224 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to obtain anaerobic bacterial suspension microspheres; Step 2. Prepare 840 mL of aerobic bacterial suspension (360 mL of actinomycete suspension, 240 mL of Bacillus subtilis suspension, 120 mL of nitrogen-fixing bacteria suspension, and 120 mL of yeast suspension) and 1120 mL of chitosan solution, mix 280 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, and then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-drying to obtain a composite fermentation agent. Comparative Example 1 The difference between this comparative example and Example 11 is that the waterborne polyurethane is not modified in the preparation method of the composite fermentation bacterial agent. A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn straw and 10kg cow dung were mixed evenly, and then 4kg biochar was added, the carbon-nitrogen ratio was adjusted to 23:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 2.2kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 90 mL of anaerobic bacterial suspension (15 mL of Clostridium cellulolyticum suspension, 30 mL of Clostridium pasteurianum suspension, 30 mL of Clostridium youngdae suspension, and 15 mL of sulfur-oxidizing bacteria suspension) and 360 mL of aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension drop by drop into the modified aqueous polyurethane membrane liquid to prepare anaerobic bacterial suspension microspheres; Step 2. Prepare 1350 mL of aerobic bacterial suspension (400 mL of actinomycete suspension, 200 mL of Bacillus subtilis suspension, 200 mL of nitrogen-fixing bacteria suspension, 400 mL of yeast suspension) and 1800 mL of chitosan solution, mix 450 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-dry to obtain a composite fermentation agent. Comparative Example 2 The difference between this comparative example and Example 11 is that the composite fermentation bacterial agent does not adopt an inner and outer double membrane coating structure. A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn straw and 10kg cow dung were mixed evenly, and then 4kg biochar was added to adjust the carbon-nitrogen ratio to 23:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 2.2kg of composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 90 mL of anaerobic bacterial suspension (15 mL of Clostridium cellulolyticum suspension, 30 mL of Clostridium pasteurianum suspension, 30 mL of Clostridium ljungdahlii suspension, and 15 mL of sulfur-oxidizing bacteria suspension); Step 2. Prepare 1350 mL of aerobic bacterial suspension (400 mL of actinomycete suspension, 200 mL of Bacillus subtilis suspension, 200 mL of nitrogen-fixing bacteria suspension, and 400 mL of yeast suspension), mix them evenly, and perform vacuum concentration and freeze-drying to obtain a composite fermentation agent. Comparative Example 3 The difference between this comparative example and Example 11 is that the compost turning operation is performed during the cow dung fermentation process. A high-efficiency and low-pollution method for returning cow dung to fields comprises the following steps: S1. 30kg corn straw and 10kg cow dung were mixed evenly, and then 4kg biochar was added to adjust the carbon-nitrogen ratio to 23:1, and then water was added to adjust the moisture content to 55% to obtain a cow dung fermentation base; S2. Add 2.2kg composite fermentation agent to the cow dung fermentation base, mix well, place in a fermentation tank for fermentation, turn the pile every 5 days to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The preparation method of the above-mentioned composite fermentation agent is as follows: Step 1. Prepare 90 mL of anaerobic bacterial suspension (15 mL of Clostridium cellulolyticum suspension, 30 mL of Clostridium pasteurianum suspension, 30 mL of Clostridium youngdae suspension, and 15 mL of sulfur-oxidizing bacteria suspension) and 360 mL of modified aqueous polyurethane membrane liquid, and add the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to obtain anaerobic bacterial suspension microspheres; Step 2. Prepare 1350 mL of aerobic bacterial suspension (400 mL of actinomycete suspension, 200 mL of Bacillus subtilis suspension, 200 mL of nitrogen-fixing bacteria suspension, 400 mL of yeast suspension) and 1800 mL of chitosan solution, mix 450 mL of anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise to the chitosan solution, perform vacuum concentration, and freeze-dry to obtain a composite fermentation agent. Performance Testing (1) Sensory evaluation The sensory properties of Examples 1-13 and Comparative Examples 1-3 were qualitatively evaluated by manual discrimination, wherein the colors were divided into yellow-brown, dark brown and dark brown; the odors were divided into odor, slight ammonia, slight odor, slight earthy odor and earthy odor; and the particle sizes were divided into lumpy, blocky and non-lumpy (loose). (2) Moisture content The moisture content of Examples 1-13 and Comparative Examples 1-3 was determined with reference to NY / T 302-1995 "Determination of moisture in organic fertilizers". (3) pH value Weigh 2 g of sample, put it into a centrifuge tube, add distilled water, tighten the lid, shake on a vortex shaker, let it stand, take the supernatant, and measure with a pH meter. (4) Carbon-nitrogen ratio (C / N) The C / N of Examples 1-13 and Comparative Examples 1-3 was calculated from total organic carbon / total nitrogen, where the total organic carbon (TOC) was determined by weighing 5 g of air-dried sample, extracting it with 1 mol / L KCl solution at an extraction ratio of 1:20, shaking for 20 min, filtering, and diluting it 100 times for determination using a total organic carbon analyzer; total nitrogen was determined using the Kjeldahl method. (5) Organic matter The organic matter determination of Examples 1-13 and Comparative Examples 1-3 was carried out with reference to NY / T 525-2021 "Organic Fertilizer". (6) Seed germination rate (GI) Weigh 10 g of sample, add 100 mL of distilled water to extract, shake for 20 minutes and filter for use, put a piece of filter paper of corresponding size in the culture dish, evenly put 10 soybean seeds with full grains and similar sizes, use a pipette to draw 5.0 mL of extract into the culture dish, use distilled water as a control, culture in a 25°C biochemical incubator for 24 hours, measure the root length and seed germination rate, the specific calculation formula is: GI = (germination rate of sample treatment × average root length of sample treatment) / (germination rate of blank × average root length of sample treatment) × 100%. (7) Ascaris egg mortality The Ascaris egg mortality rate of Examples 1-13 and Comparative Examples 1-3 was determined with reference to GB / T19524.2 "Determination of Ascaris egg mortality rate in fertilizers". (8) Fecal coliform count The fecal coliform counts of Examples 1-13 and Comparative Examples 1-3 were determined with reference to GB / T19524.1 "Determination of fecal coliforms in fertilizers". Table 1 Relevant evaluation indexes of Examples 1-13 and Comparative Examples 1-3 As shown in Table 1, the sensory evaluation, moisture content, pH, C / N, organic matter, GI, ascaris egg mortality, and fecal coliform count of Examples 1-13 are all better than those of Comparative Examples 1-3, among which the moisture content, organic matter, GI, ascaris egg mortality, and fecal coliform count are all higher than those of Comparative Examples 1-3. 525-2021 "Organic Fertilizer" standard limit, indicating that the cow dung organic fertilizer produced by the method provided by this patent can meet the standard requirements of organic fertilizer and be applied to the soil to promote crop growth; and comparative example 1 is an unmodified aqueous polyurethane with an anaerobic bacterial inner layer coating structure, and comparative example 2 is an anaerobic and aerobic bacteria added together, indicating that anaerobic bacteria in cow dung will die to a certain extent under normoxic conditions in the early stage of composting and the high temperature period, which has a great impact on the formation of mature matter in the mature period, thereby reducing the fermentation efficiency and causing the quality of the cow dung organic fertilizer to deteriorate; comparative example 3 adopts manual composting operation during composting, and the quality of its cow dung organic fertilizer is no different from that prepared in the embodiment, indicating that the method provided by the present invention can reduce the labor cost in the preparation process of cow dung organic fertilizer, save the operation links in the preparation process of cow dung organic fertilizer, and does not reduce the quality of cow dung organic fertilizer. (9) Temperature measurement Use a thermocouple thermometer, insert it vertically from the top of the pile to a depth of 20-30cm, measure the temperature of the pile center, 10cm to the left and 10cm to the right of the center, calculate the average temperature, and use it as the temperature of the compost fermentation day. Table 2 Temperature changes during composting of Example 11 and Comparative Examples 1-3 characteristic Embodiment 11 Comparative Example 1 Comparative Example 2 Comparative Example 3 Time required to reach 50℃ (days) 2.5 4 5 3 Time above 50℃ (days) 10 8 6 9 Maximum temperature(℃) 68.5 62.4 61.3 64.3 Time required to reach the maximum temperature (days) 6 8 8 6 Depend on Figure 1 It can be seen that Example 11 and Comparative Examples 1-3 all experience a heating period, a high temperature period and a cooling period, wherein the heating rate and the high temperature period maintenance time of Example 11 are both greater than those of Comparative Examples 1-3, indicating that the composite fermentation agent encapsulating anaerobic bacteria and aerobic bacteria releases aerobic bacteria to decompose organic matter in cow dung during the heating period, causing the temperature of the cow dung pile to rise rapidly, and entering the high temperature period for fermentation and maturity in advance, while the co-release of anaerobic bacteria and aerobic bacteria in Comparative Examples 1 and 2 will greatly affect the metabolic decomposition of aerobic bacteria, thereby affecting the efficiency of decomposition of organic matter in cow dung and prolonging the time to enter the high temperature period. Comparative Example 3 adopts manual compost turning operation, and its heating rate is not significantly different from that of Example 11. As can be seen from Table 2, all the characteristics of Example 11 during the composting process are better than those of Comparative Examples 1-3, indicating that in Example 11, in the high temperature period, the aerobic bacteria maximize the utilization of organic matter in cow dung, the microorganisms in the fermentation environment system tend to be saturated, and the temperature is in a high temperature equilibrium state. At the same time, in the cooling period and the maturity period, the oxygen demand decreases, causing the fermentation system environment to be transformed into a low oxygen condition, the azobenzene in the modified waterborne polyurethane that encapsulates the anaerobic bacteria is activated by low oxygen, the chemical bonds in the groups are broken, the modified waterborne polyurethane disintegrates, and the anaerobic bacteria in the composite fermentation agent are released to promote the conversion of low molecular weight substances into humus, thereby shortening the maturity time. (10) Electrical conductivity (EC) Weigh 1 g of sample and mix it with 10 mL of distilled water in a 50 mL Erlenmeyer flask. Oscillate it continuously on a shaker at room temperature for 30 min. After standing, filter the filtrate and measure the conductivity with a conductivity meter. (11) Humic ratio (E4 / E6) Weigh 1.0 g of sample and mix it with 20 mL of distilled water for extraction. Take the supernatant after centrifugation and measure the absorbance at 465 and 665 nm using a spectrophotometer to calculate the humification ratio (E4 / E6). (12) Fast-acting phosphorus and fast-acting potassium The available phosphorus of Example 11 and Comparative Examples 1-3 was determined with reference to NY / T 300-1995 "Determination of Available Phosphorus in Organic Fertilizers", and the available potassium of Example 11 and Comparative Examples 1-3 was determined with reference to NY / T 301-1995 "Determination of Available Potassium in Organic Fertilizers". Depend on Figure 2It can be seen that the total nitrogen, available phosphorus and available potassium of Example 11 are higher than those of Comparative Examples 1-3, and the electrical conductivity and humus ratio are lower than those of Comparative Examples 1-3, indicating that the quality and maturity of the cow dung organic fertilizer prepared in Example 11 are higher than those of Comparative Examples 1-3, indicating that the strain stage release of the composite fermentation bacteria agent can maximize the utilization of aerobic bacteria under normoxic conditions to decompose organic matter in cow dung into small molecules, release anaerobic bacteria under hypoxic conditions and promote the rate of humus production, and utilize the corresponding anaerobic bacteria for nitrogen fixation and carbon fixation to reduce carbon and nitrogen losses and ensure the quality of cow dung organic fertilizer. The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A high-efficiency and low-pollution method for returning cow dung to fields, characterized in that: The following steps are involved: S1. The corn stalks and biochar were mixed evenly with cow dung, the carbon-nitrogen ratio was adjusted to (20-30): 1, and then water was added to adjust the moisture content to 50-65% to obtain a cow dung fermentation base; S2. Add the composite fermentation agent to the cow dung fermentation base, mix well, and place in a fermentation tank for fermentation to obtain cow dung fermentation mature material; S3. The fermented and decomposed cow dung material is dried, collected and packaged to obtain cow dung organic fertilizer; The composite fermentation bacterial agent is composed of aerobic bacteria and anaerobic bacteria, wherein the aerobic bacteria are composed of actinomycetes, bacillus subtilis, nitrogen-fixing bacteria and yeast, and the anaerobic bacteria are composed of clostridium cellulolyticum, clostridium pasteurianum, clostridium ljungdahlii and sulfur-oxidizing bacteria.

2. The method for returning cow dung to the field with high efficiency and low pollution according to claim 1 is characterized in that: In step S1, the ratio of corn straw to cow dung is (3-1):(1-2), and the amount of biochar added is 5-15%, based on the total weight of corn straw and cow dung.

3. The method for returning cow dung to the field with high efficiency and low pollution according to claim 1 is characterized in that: The inoculation amount of the composite fermentation bacteria agent in step S2 is 1-5%.

4. The high-efficiency and low-pollution method for returning cow dung to fields according to claim 1, characterized in that: The method for preparing the composite fermentation agent in step S2 comprises the following steps: Step 1. preparing an anaerobic bacterial suspension and a modified aqueous polyurethane membrane liquid, and adding the anaerobic bacterial suspension dropwise into the modified aqueous polyurethane membrane liquid to obtain anaerobic bacterial suspension microspheres; Step 2. Prepare aerobic bacterial suspension and chitosan solution, mix the anaerobic bacterial suspension microspheres and aerobic bacterial suspension evenly, then add dropwise into the chitosan solution, perform vacuum concentration and freeze drying, and obtain the composite fermentation agent.

5. The high-efficiency and low-pollution method for returning cow dung to fields according to claim 4 is characterized in that: The preparation method of the modified waterborne polyurethane in step 1 is to firstly mix the waterborne polyurethane and 4,4'-dihydroxyazobenzene in a mass ratio of 1:(2-4), stir at 60°C until completely dissolved, then add 10-20% bayberry tannin, heat to 120-150°C and keep for 20-40 minutes, cool and dry to obtain the modified waterborne polyurethane.

6. The high-efficiency and low-pollution method for returning cow dung to the field according to claim 4, characterized in that: The anaerobic bacterial suspension in step 1 is composed of a suspension of Clostridium cellulolyticum, a suspension of Clostridium pasteurianum, a suspension of Clostridium ljungdahlii and a suspension of sulfur-oxidizing bacteria, and the ratio thereof is (1-3):(0.5-2):(1-2):(0.5-1.5), and the bacterial concentration thereof is (10-15)×10 8 CFU / mL.

7. The high-efficiency and low-pollution method for returning cow dung to fields according to claim 4, characterized in that: In the step 1, the ratio of the anaerobic bacterial suspension to the modified aqueous polyurethane membrane liquid is 1:(2-5).

8. The high-efficiency and low-pollution method for returning cow dung to fields according to claim 4, characterized in that: In step 2, the aerobic bacterial suspension is composed of an actinomycete suspension, a Bacillus subtilis suspension, a nitrogen-fixing bacteria suspension and a yeast suspension, and the ratio thereof is (1-4):(1-3):(0.5-1.5):(1-3), and the bacterial concentration is (5-15)×10 10 CFU / mL.

9. The high-efficiency and low-pollution method for returning cow dung to fields according to claim 4, characterized in that: In step 2, the ratio of the anaerobic bacteria suspension microspheres, the aerobic bacteria suspension and the chitosan solution is (1-3):(2-4):(1-5).

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