Method for preparing organic fertilizer by using kitchen waste anaerobic sludge and application thereof

Abstract

The present application belongs to the technical field of organic solid waste resource utilization and organic fertilizer preparation, and particularly relates to a method for preparing organic fertilizer by using kitchen waste anaerobic biogas residue and application thereof. The present application takes kitchen waste anaerobic biogas residue as the main raw material, and mixes rice husk and rice bran formed by waste such as rice husk and rice bran at a weight ratio of 6-7:3-4, adjusts the initial moisture content to 55%-65%, and the carbon-nitrogen ratio to 20-35:1. Then, aerobic fermentation is carried out, and the process sequentially goes through the stages of temperature rise, 55-70 DEG C high-temperature decomposition, temperature drop, maturity and aging, wherein the high-temperature decomposition stage lasts for 7-10 days, and the temperature and oxygen supply are controlled by regular turning over. Finally, the organic fertilizer is obtained by crushing and screening. The present application also provides specific application of the organic fertilizer in tea and citrus mountain planting. The present application realizes efficient resource utilization of kitchen waste anaerobic biogas residue, and the prepared organic fertilizer can effectively improve the mountain soil and improve the soil fertility, and has significant environmental, economic and social benefits.

Description

Technical Field

[0001] This invention belongs to the field of organic solid waste resource utilization and organic fertilizer preparation technology, specifically involving a method for preparing organic fertilizer using kitchen waste anaerobic digestate and its application. Background Technology

[0002] Currently, the mainstream treatment technology for kitchen waste in China is anaerobic fermentation. This technology decomposes organic matter in kitchen waste through microorganisms, producing clean energy biogas and realizing the resource utilization of kitchen waste. However, this process also generates a large amount of byproducts—anaerobic digestate. Due to its high moisture content (typically 80%-90%), dense structure, severely low carbon-to-nitrogen ratio (C / N) (mostly around 6:1), and the presence of unstabilized organic matter, parasite eggs, and pathogenic microorganisms, its direct land use is severely limited. Currently, the vast majority of kitchen waste treatment companies in China dispose of digestate through landfill or incineration. Landfilling not only occupies valuable land resources but also produces high-concentration leachate, increasing the burden on subsequent treatment; incineration, due to the high moisture content and low calorific value of the digestate, easily corrodes incinerator equipment, increasing operating costs and maintenance difficulties. Therefore, there is an urgent need to develop green and efficient resource-based disposal pathways for anaerobic digestate.

[0003] In existing technologies, aerobic composting of biogas residue is an important research direction. For example, patent document CN111995476A discloses a method for preparing organic fertilizer from biogas residue of kitchen waste, which involves composting kitchen waste lactic acid fermentation liquid, sawdust, bentonite, and other composite conditioners. Patent document CN115231972A also discloses a method for preparing organic fertilizer from kitchen waste through anaerobic fermentation, which involves separating the oil and water in kitchen waste, followed by anaerobic fermentation, and then mixing the biogas residue and organic solid waste together for aerobic composting. These technologies generally use sawdust, straw, rice husks, etc., as auxiliary materials to adjust the moisture content and carbon-nitrogen ratio of the compost material. However, practice and research have found that although sawdust has a high C / N ratio and high porosity, its high lignin content and dense structure make it difficult for aerobic microorganisms to quickly colonize and degrade it. This results in insufficient heat generation during the composting start-up phase, slow temperature rise in the compost pile, and often an inability to reach the high-temperature decomposition stage above 55°C within 24-48 hours, or the high-temperature duration is less than 3 days. This makes it difficult to effectively kill pathogens and parasite eggs, leading to incomplete composting and a prolonged cycle. More importantly, the selection and proportioning of auxiliary materials in existing technologies often only focus on moisture content or C / N adjustment, lacking precise matching for the dual constraints of "high moisture content + low C / N" in kitchen waste anaerobic digestate. This results in a high composting failure rate in actual engineering projects, failing to meet the requirements of large-scale, engineering applications.

[0004] In summary, how to develop an organic fertilizer production method that can accurately adapt to the physicochemical properties of kitchen waste anaerobic digestate, achieve rapid start-up of high-temperature fermentation, and ensure thorough composting has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing organic fertilizer from kitchen waste anaerobic digestate and its application. It offers a highly efficient, low-cost, and thoroughly harmless method for producing organic fertilizer from digestate, achieving efficient and stable resource utilization of kitchen waste anaerobic digestate. The resulting organic fertilizer is suitable for improving mountain soils.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing organic fertilizer using anaerobic digestate from kitchen waste includes the following steps: S1. Raw materials: Anaerobic digestate from kitchen waste is the digestate produced after anaerobic fermentation of kitchen waste. Its moisture content is 80-90%, carbon-nitrogen ratio is 5-6:1, and organic matter content is 27-32%. S2. Ingredients: Mix kitchen waste anaerobic digestate with rice bran at a weight ratio of 6-7:3-4 to obtain a compound; the rice bran is a mixture of rice husks and rice bran produced during rice processing. S3. Aerobic fermentation: The compound obtained in step S2 is subjected to aerobic fermentation, which includes a heating stage, a high-temperature decomposition stage, a cooling and maturation stage and an aging stage in sequence to obtain the aged material; wherein, the temperature of the high-temperature decomposition stage is 55~70℃, the duration is 7~10 days, and the material is turned over every 2~3 days during this stage.

[0007] S4. Post-processing: The material aged in step S3 is crushed and screened to obtain organic fertilizer.

[0008] Anaerobic digestate from kitchen waste refers to the solid byproduct obtained after kitchen waste undergoes anaerobic fermentation (approximately 40 days) to produce biogas, followed by two-phase separation and sedimentation. It mainly consists of organic matter that is difficult to degrade further, residual microbial cells, and inorganic minerals. This digestate has the following typical characteristics: high water content, dense structure, and a severely imbalanced carbon-to-nitrogen ratio; it is also rich in organic matter, nitrogen and phosphorus elements, and various trace elements necessary for plant growth. However, the digestate also contains unstabilized organic matter, parasite eggs, and pathogenic microorganisms, among other harmful components. These characteristics endow anaerobic digestate with significant land use potential, but also significantly limit its direct agricultural application.

[0009] This invention addresses the dual requirements of aerobic composting for material moisture content and carbon-to-nitrogen ratio. It provides auxiliary materials with a high carbon-to-nitrogen ratio (C / N, the mass ratio of carbon to nitrogen), high porosity, and low moisture content for anaerobic digestate from kitchen waste. Simultaneously, it utilizes the metabolic activity of aerobic microorganisms within the kitchen waste anaerobic digestate to further decompose residual organic matter, thereby promoting deep composting, effectively killing pathogenic microorganisms, and ultimately transforming it into stable and safe organic fertilizer.

[0010] To address the high moisture content of anaerobic digestate from kitchen waste, this invention first determined the optimal weight ratio of digestate to rice bran for co-composting to be 6-7:3-4 through component analysis of the auxiliary materials and digestate, theoretical calculations, and a series of composting experiments. This ratio allows the initial moisture content of the compounded material to be adjusted to 55%-65% without the need for additional water. Among the combinations meeting the moisture content requirements, combinations with a carbon-to-nitrogen ratio (C / N) within the range of 20-35:1 were further selected as the final ratio. Following this, aerobic fermentation is carried out, utilizing aerobic microorganisms to decompose, transform, and stabilize the organic waste through a biological treatment process.

[0011] During the heating phase, under the aforementioned moisture content and carbon-nitrogen ratio, mesophilic bacteria and fungi become the dominant force, rapidly growing and decomposing organic matter and releasing heat. The initial pile body heats up to above 55°C within 24 hours.

[0012] The high-temperature decomposition stage is a crucial step in aerobic fermentation. During this stage, maintaining the pile temperature within the range of 55-70℃ for 7-10 days effectively kills pathogens, weed seeds, and insect eggs. At this time, thermophilic bacteria and thermophilic actinomycetes become the dominant microorganisms, primarily decomposing recalcitrant organic matter such as cellulose and lignin, promoting the deep transformation of organic matter: complex organic matter is decomposed into smaller molecules such as CO2, H2O, and NH3, while some intermediate products are synthesized into humus. During the high-temperature decomposition process, continuous temperature monitoring is necessary, with daily measurement of the pile's center temperature to prevent temperatures from exceeding 70℃, which could lead to microbial inactivation or death. During the high-temperature stage where the pile temperature is maintained above 55℃, the pile should be turned over every 2-3 days to break up the surface crust, release excess heat, and replenish oxygen.

[0013] Preferably, the rice husk in step S2 has a moisture content of 5-7%, a carbon-to-nitrogen ratio of 40-50:1, and an organic matter content of 55-60%.

[0014] During the processing of rice into rice, waste products such as rice husks and rice bran (referred to as rice bran) are produced. This waste has a low moisture content of 5% to 7%, a high carbon-to-nitrogen ratio of 40 to 50:1, and a high organic matter content of 55% to 60%. It is highly absorbent, loose and porous, and has a large surface area, making it suitable for kitchen waste anaerobic digestate, which has the characteristics of high moisture content, low carbon-to-nitrogen ratio, low organic matter, viscosity, and fine particles.

[0015] Preferably, in step S2, anaerobic digestate from kitchen waste with a moisture content of 80-90% and a carbon-to-nitrogen ratio of 5-6:1 is mixed evenly with rice bran with a moisture content of 5%-7% and a carbon-to-nitrogen ratio of 40-50:1 at a weight ratio of 6-7:3-4. During mixing, the anaerobic digestate from kitchen waste is added to the rice bran in three batches and stirred until evenly mixed, resulting in a compound with a moisture content of 55%-65%, a carbon-to-nitrogen ratio of 20-35:1, and a porosity of 30-0%.

[0016] Preferably, the specific process of the heating stage in step S3 is as follows: the compound obtained in step S2 is heated to above 55°C within 24 hours. At this time, mesophilic bacteria and fungi begin to decompose easily degradable organic matter such as sugars, starches, and proteins, releasing heat, and the temperature of the pile rises to above 55°C.

[0017] Preferably, the specific process of the high-temperature decomposition stage in step S3 is as follows: the temperature of the pile is raised to 55~70℃, and it is turned over and thrown every 2~3 days, with the high temperature lasting for 7~10 days.

[0018] Preferably, the specific process of the cooling and maturation stage in step S3 is as follows: when the temperature of the pile obtained in the high-temperature decomposition stage drops to the range of 45℃~55℃, it is turned over and dumped every 3~4 days for a period of 10~15 days.

[0019] After the high-temperature decomposition stage, the temperature of the compost pile begins to gradually decrease. When the temperature drops to the range of 45-55℃, mesophilic bacteria and fungi regain become the dominant microbial population, continuing to decompose the remaining organic matter. During this stage, the rate of humus synthesis accelerates significantly, the physical structure of the compost stabilizes, the color gradually changes from yellowish-brown to dark brown, and the odor changes from a pungent smell to an earthy smell.

[0020] Preferably, in step S3, the aging stage is a cooling and maturation stage. After the product is cooled to below 45°C, it is turned over every 5 to 7 days, and the aging time is 25 to 30 days, with the moisture content reduced to below 30%.

[0021] Preferably, the total time for the aerobic fermentation stage in step S3 is 43 to 56 days.

[0022] The present invention also provides an organic fertilizer prepared using the method described above.

[0023] The present invention also provides an application of the aforementioned organic fertilizer in the cultivation of tea-branch citrus in mountainous areas.

[0024] Preferably, the specific operation process of the application is as follows: the organic fertilizer is spread in a circle on the soil surface under the drip line of the tea branch tangerine, with an application amount of 8-12 kg per tree each time, and fertilization is carried out 3-5 times a year.

[0025] To expand the scale of the Chenpi industry, taking the Chazhigan (Citrus reticulata Blanco cv. Chachi) in Xinhui District, Jiangmen City, Guangdong Province as an example, the local area is vigorously promoting the "cultivation of Chazhigan on mountains". However, the mountain soil generally has problems such as thin soil layer, low organic matter content, and poor fertilizer and water retention capacity. The long-term single application of chemical fertilizers has led to increased soil compaction and severe acidification, and caused agricultural non-point source pollution. At present, there is still a lack of organic fertilizer products on the market that are specifically designed for the mountain cultivation of Chazhigan and prepared based on local organic waste (such as kitchen waste biogas residue), and a regional closed-loop circular economy model of "urban kitchen waste disposal - biogas residue resource-based fertilizer production - characteristic agriculture targeted farmland return" has not been formed.

[0026] The organic fertilizer prepared by the present invention is applied in the way of spreading in a circle around the soil surface at the drip line of the Chazhigan tree, with a dosage of 8 - 12 kg per tree, 3 - 5 times a year. It can effectively improve the pH value, organic matter, humus, and the content of various nutrients such as available potassium, available phosphorus, exchangeable calcium, exchangeable magnesium, and available boron in the mountain soil, relieve soil acidification and compaction, reduce the dependence on chemical fertilizers, and thus realize the closed-loop circular economy model of "biogas residue resource-based fertilizer production for kitchen waste - characteristic agriculture targeted farmland return".

[0027] Compared with the prior art, the present invention has the following technical advantages: (1) High-efficient resource utilization: For the first time, aiming at the specific physical and chemical properties of kitchen waste anaerobic biogas residue (high water content, low C / N, and dense structure), rice bran is screened out as the best matching auxiliary material, and the precise co-composting ratio is determined, realizing energy-saving aerobic fermentation without additional water replenishment and without adding external carbon source to adjust C / N, overcoming the technical problem that conventional auxiliary materials such as wood chips cannot initiate high-temperature fermentation. (2) Significant environmental benefits: It reduces the secondary pollution caused by landfill or incineration of kitchen waste anaerobic biogas residue, and at the same time reduces the carbon emissions in the production and use process of chemical fertilizers.

[0028] (3) Outstanding soil improvement effect: After applying the organic fertilizer of the present invention, many indexes of the mountain soil of Chazhigan, such as pH value, organic matter, humus, available potassium, available phosphorus, exchangeable calcium, exchangeable magnesium, and available boron, have been significantly improved, which can effectively improve the mountain soil and enhance soil fertility. Detailed implementation manners

[0029] The present invention will be further described below in conjunction with embodiments. The embodiments are for making the present invention easier to understand, rather than limiting the present invention. Those skilled in the art can make various modifications according to the basic idea of the present invention, but as long as they do not depart from the basic idea of the present invention, they are within the scope of the present invention.

[0030] The preparation process of anaerobic digestate of kitchen waste in this experiment is as follows: The digestate produced after 40 days of anaerobic fermentation of food scraps and food processing waste collected from restaurants and canteens (including discarded vegetable leaves, leftover food, leftover rice, fruit peels, eggshells, tea dregs, bones, etc.) is collected.

[0031] The preparation process of the rice bran is as follows: The process of processing rice into rice and the waste generated: (1) Rice wind separation removes impurities and produces waste: straw (a very small amount, most of which is removed in the field); (2) Rice dehulling removes the outer husk of the rice grains, and the resulting waste is rice husk; (3) Separation of brown rice and unhulled husks, the waste product is: husks; (4) Milling rice removes the bran layer from the surface of brown rice. The waste product is the bran layer.

[0032] The waste produced from the above four steps is mixed to obtain rice bran.

[0033] Before the experiment, the physicochemical properties of the collected kitchen waste anaerobic digestate and rice husk were analyzed and tested. The results are shown in Table 1 and Table 2 below.

[0034] Table 1. Physicochemical Properties Analysis of Kitchen Waste Anaerobic Digester Sludge, the Raw Material for Organic Fertilizer of this Invention

[0035] Table 2 Physicochemical properties of rice bran

[0036] Example 1: A method for preparing organic fertilizer using anaerobic digestate from kitchen waste. The method for preparing organic fertilizer using anaerobic digestate from kitchen waste includes the following steps: S1~S2, Raw materials and ingredients: Take 4.2 tons of collected kitchen waste anaerobic digestate and 1.8 tons of rice bran, mix them evenly, so that the moisture content of the compound is adjusted to 61%, the carbon-nitrogen ratio is adjusted to 22:1, and the porosity is 35%, to obtain the compound; S3. Aerobic Fermentation: The compound obtained in step S2 is placed in an aerobic fermentation tank. The aerobic fermentation includes a heating stage, a high-temperature decomposition stage, a cooling and maturation stage, and an aging stage, respectively, to obtain the aged material. The specific process is as follows: Heating phase: Increase the temperature of the aerobic fermentation tank to 63℃ within 24 hours; High-temperature decomposition stage: After the temperature is raised to 63℃, turn the food over every 2 days. On the 11th day, the temperature drops to 55℃, and the cooling and decomposition stage begins. Cooling and composting stage: When the compost temperature drops to between 45℃ and 55℃, turn it over every 4 days. On the 24th day, when the temperature drops to 45℃, it enters the aging stage. Aging stage: After the temperature drops below 45℃, turn the leaves over every 7 days for a total of 30 days of aging, until the moisture content drops below 30%. S4. Post-processing: The material aged in step S2 is crushed and screened to obtain organic fertilizer.

[0037] Example 2: A method for preparing organic fertilizer using anaerobic digestate from kitchen waste. The method for preparing organic fertilizer using anaerobic digestate from kitchen waste includes the following steps: S1. Mixing: Take 3.6 tons of collected kitchen waste anaerobic digestate and 2.4 tons of rice bran, mix them evenly, adjust the moisture content of the compound to 56%, the carbon-nitrogen ratio to 27:1, and the porosity to 33% to obtain the compound; S2. Aerobic Fermentation: The compound obtained in step S1 is placed in an aerobic fermentation tank. The aerobic fermentation includes a heating stage, a high-temperature decomposition stage, a cooling and maturation stage, and an aging stage, respectively, to obtain an aged material. The specific process is as follows: Heating phase: Increase the temperature of the aerobic fermentation tank to 60℃ within 24 hours; High-temperature decomposition stage: After the temperature is raised to 60℃, turn the food over every 2 days. On the 10th day, the temperature drops to 55℃, and the cooling and decomposition stage begins. Cooling and composting stage: When the compost temperature drops to between 45℃ and 55℃, turn it over every 4 days. On the 23rd day, when the temperature drops to 45℃, it enters the aging stage. Aging stage: After the temperature drops below 45℃, turn the leaves over every 7 days for a total of 26 days, until the moisture content drops below 30%. S3. Post-processing: The material aged in step S2 is crushed and screened to obtain organic fertilizer.

[0038] Example 3: A method for preparing organic fertilizer using anaerobic digestate from kitchen waste. The method for preparing organic fertilizer using anaerobic digestate from kitchen waste includes the following steps: S1. Mixing: Take 6.5 tons of collected kitchen waste anaerobic digestate and 3.5 tons of rice bran, mix them evenly, adjust the moisture content of the compound to 57%, and adjust the carbon-nitrogen ratio to 24:1 to obtain the compound. S2. Aerobic Fermentation: The compound obtained in step S1 is placed in an aerobic fermentation tank. The aerobic fermentation includes a heating stage, a high-temperature decomposition stage, a cooling and maturation stage, and an aging stage, respectively, to obtain an aged material. The specific process is as follows: Heating phase: Increase the temperature of the aerobic fermentation tank to 62℃ within 24 hours; High-temperature decomposition stage: After the temperature is raised to 62℃, turn the food over every 2 days. On the 9th day, the temperature drops to 55℃, and the cooling and decomposition stage begins. Cooling and composting stage: When the compost temperature drops to between 45℃ and 55℃, turn it over every 4 days. On the 24th day, when the temperature drops to 45℃, it enters the aging stage. Aging stage: After the temperature drops below 45℃, turn the leaves over every 7 days for a total of 25 days, until the moisture content drops below 30%. S3. Post-processing: The material aged in step S2 is crushed and screened to obtain organic fertilizer.

[0039] Comparative Example 1: A method for preparing organic fertilizer from kitchen waste anaerobic digestate Because sawdust has a higher carbon-to-nitrogen ratio than rice husks, it is considered an ideal carbon source and leavening agent for aerobic organic composting. It is often used as a conditioner to provide abundant porosity and carbon source for composting, thereby promoting the growth and metabolism of microorganisms. Therefore, this comparative example uses sawdust (pine sawdust from a wood processing plant) instead of rice husks as an auxiliary material.

[0040] The physicochemical properties of the sawdust were tested and analyzed before the experiment, and the results are shown in Table 3.

[0041] Table 3 Physicochemical Properties Analysis of Wood Chips

[0042] The specific preparation process is as follows: Take 0.7 tons of collected kitchen waste anaerobic digestate and 0.3 tons of sawdust, mix them evenly, then adjust the moisture content to 65%, the carbon-nitrogen ratio to 28:1, and the porosity to 35%. Then place the compound in an aerobic fermentation tank. Within 24 hours, the temperature of the pile rises to 45℃. It can only be maintained at 45℃ for 2 days. Then the temperature of the pile begins to drop, and the pile cannot enter the high-temperature stage, resulting in composting failure.

[0043] Comparative Example 2: A method for preparing organic fertilizer using anaerobic digestate from kitchen waste. The method for preparing organic fertilizer using anaerobic digestate from kitchen waste is as follows: S1. Mixing: Take 3 tons of collected kitchen waste anaerobic digestate and 3 tons of rice bran, mix them evenly, adjust the moisture content of the compound to 45%, the carbon-nitrogen ratio to 32:1, and the porosity to 28% to obtain the compound. S2, Aerobic Fermentation: The compound obtained in step S1 was placed in an aerobic fermentation tank. The temperature was raised to 48°C on the first day, then to 53°C on the third day, and then began to decrease on the fourth day. The experiment failed because it did not enter the high-temperature decomposition stage.

[0044] Comparative Example 3: A method for preparing organic fertilizer using anaerobic digestate from kitchen waste. The method for preparing organic fertilizer using anaerobic digestate from kitchen waste is as follows: S1. By naturally drying, the moisture content of anaerobic digestate from kitchen waste was reduced from 85% to 75%, and the carbon-to-nitrogen ratio was increased from 6.15 to 10.91. S2. Mixing: Take 4.8 tons of collected kitchen waste anaerobic digestate and 1.8 tons of rice bran, mix them evenly, adjust the moisture content of the compound to 62%, and adjust the carbon-nitrogen ratio to 18:1 to obtain the compound. S3. Aerobic fermentation: The compound obtained in step S2 was placed in an aerobic fermentation tank. On the first day, the temperature was raised to 46°C and then maintained at around 45°C. The high-temperature decomposition stage was not entered, and the experiment failed.

[0045] Experimental Application Cases Referring to the People's Republic of China agricultural industry standard NY / T525-2021 "Organic Fertilizer", the fertilizers prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were tested, and the test results are shown in Table 4.

[0046] Table 4. Test results of different fertilizers according to the present invention

[0047] After the testing was completed, the fertilizers from the above three examples were used in a planting experiment on mountainous areas of tea-branch citrus. The specific process is as follows: Location: Shijian Plantation, Xinhui District, Jiangmen City, soil from the mountainous area of ​​Chazhigan oranges; Fertilization plan: On September 20, 2025, take 6 tea branch tangerine trees, 2 trees per group, and then spread the above-mentioned organic fertilizer in a circle on the soil surface at the drip line position of the tea branch tangerine trees, with an application amount of 10 kg per tree.

[0048] Effectiveness Verification: Soil surface (approximately 10 cm) samples were collected before fertilization (September 19, 2025) and approximately four months after fertilization (January 21, 2026) for testing. The tested indicators included pH, organic matter, humus, available potassium, available phosphorus, exchangeable calcium, exchangeable magnesium, and available boron (nitrogen content was not tested because nitrogen fertilizer was applied during both soil sampling periods). The testing methods adopted industry standard methods, as detailed below: Soil pH was determined using the electrode potential method; Organic matter and humus were determined by potassium dichromate titration method; Available phosphorus was determined by hydrochloric acid-sulfuric acid extraction-molybdenum antimony colorimetric method; Available potassium, exchangeable calcium, and exchangeable magnesium were determined by ammonium acetate extraction-flame photometry. Available boron was determined using EDTA-inductively coupled plasma atomic emission spectrometry.

[0049] The final test results are shown in Table 5 below.

[0050] Table 5. Soil test results of Chazhigan mountain soil samples from different embodiment groups

[0051] As shown in Table 4 above, after applying the organic fertilizers prepared in Examples 1-3 of this invention, the fertility indicators of the soil in the Chazhigan mountain area, such as pH, organic matter, humus, available potassium, available phosphorus, exchangeable calcium, exchangeable magnesium, and available boron, were significantly improved.

[0052] It should be noted that the above-described embodiments should be understood as illustrative, not as limiting the scope of protection of this invention. The scope of protection of this invention is defined by the claims. For those skilled in the art, some non-essential improvements and adjustments made to this invention without departing from the essence and scope of this invention still fall within the scope of protection of this invention.

Claims

1. A method for preparing organic fertilizer using anaerobic digestate from kitchen waste, characterized in that, Includes the following steps: S1. Raw materials: Anaerobic digestate from kitchen waste is the digestate produced after anaerobic fermentation of kitchen waste. Its moisture content is 80-90%, carbon-nitrogen ratio is 5-6:1, and organic matter content is 27-32%. S2. Ingredients: Mix kitchen waste anaerobic digestate with rice bran at a weight ratio of 6-7:3-4 to obtain a compound; the rice bran is a mixture of rice husks and rice bran produced during rice processing. S3. Aerobic fermentation: The compound obtained in step S2 is subjected to aerobic fermentation, which includes a heating stage, a high-temperature decomposition stage, a cooling and maturation stage and an aging stage in sequence to obtain the aged material; wherein, the temperature of the high-temperature decomposition stage is 55~70℃, the duration is 7~10 days, and the material is turned over every 2~3 days during this stage. S4. Post-processing: The material aged in step S3 is crushed and screened to obtain organic fertilizer.

2. The method as described in claim 1, characterized in that, The rice husks described in step S2 have a moisture content of 5-7%, a carbon-to-nitrogen ratio of 40-50:1, and an organic matter content of 55-60%.

3. The method as described in claim 1, characterized in that, The compound described in step S2 has a moisture content of 55%-65%, a carbon-nitrogen ratio of 20-35:1, and a porosity of 30-40%.

4. The method as described in claim 1, characterized in that, The specific process of the heating stage in step S3 is as follows: the compound obtained in step S2 is heated to above 55°C within 24 hours.

5. The method as described in claim 1, characterized in that, The specific process of the high-temperature decomposition stage described in step S3 is as follows: the temperature of the pile is raised to 55~70℃, and it is turned over and thrown every 2~3 days. The high temperature lasts for 7~10 days.

6. The method as described in claim 1, characterized in that, The specific process of the cooling and maturation stage in step S3 is as follows: when the temperature of the pile obtained in the high-temperature decomposition stage drops to 45℃~55℃, it is turned over and dumped every 3~4 days for a period of 10~15 days.

7. The method as described in claim 1, characterized in that, The aging stage mentioned in step S3 is the cooling and maturation stage where the product is cooled to below 45°C, turned over every 5 to 7 days, and aged for 25 to 30 days until the moisture content drops to below 30%.

8. The method as described in claim 1, characterized in that, The total time for the aerobic fermentation stage described in step S3 is 43 to 56 days.

9. An organic fertilizer prepared by the method of claim 1.

10. The application of the organic fertilizer as described in claim 9 in the planting of tea-branch citrus in mountainous areas, characterized in that, The specific operation process of the application is as follows: under the drip line of the tea branch tangerine, the organic fertilizer is spread in a circle on the soil surface. The amount applied to each tree is 8-12 kg each time, and the fertilizer is applied 3-5 times a year.

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