Method for preparing controlled-release fertilizer from organic material based on microbial fermentation

Abstract

The invention discloses a method for preparing a controlled-release fertilizer from organic materials based on microbial fermentation. The method comprises the following steps: S1, firstly, screening and proportioning the organic materials; s2, the proportioned organic materials are crushed and conditioned; s3, microbial strains are selected and rejuvenated; s4, carrying out enlarged culture on the rejuvenated microbial strains; s5, performing inoculation and mixing on the microbial strain subjected to amplification culture and the organic material in the step S2; s6, performing aerobic fermentation on the organic material inoculated and mixed in the step S5 to obtain a decomposed organic material; s7, pre-treating the decomposed organic material, and adding a controlled release agent; s8, granulating and forming the controlled-release fertilizer; and S9, drying, cooling, screening and packaging the granulated controlled-release fertilizer. The influence of particle size difference on adhesion of the controlled release agent is eliminated, uniform basic nutrients, relatively single cost, complete degradation and no residue are ensured, and the damage of high temperature to nutrients and organic matters is avoided.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of controlled-release fertilizer preparation, and particularly relates to a method for preparing controlled-release fertilizer from organic material based on microbial fermentation. BACKGROUND

[0002] Organic fertilizer is processed from animal and plant wastes and plant residues, and is rich in various organic acids, peptides, nitrogen, phosphorus and potassium after removing harmful substances, and can provide comprehensive nutrition for crops, has long fertilizer efficiency, can increase soil organic matter, and promote microbial reproduction, and beneficial microorganisms can fix nitrogen, decompose phosphorus and potassium, continuously supply nutrients for crops, and a large amount of beneficial active bacteria directly participate in processes such as energy conversion, humus formation and decomposition of soil matter, especially a large amount of extracellular polysaccharides produced in the reproduction process of active bacteria can play a role in gluing the soil aggregate structure, effectively improving the physical properties of soil, and enhancing the air permeability, water retention and fertilizer retention capacity of soil, so that the soil forms a virtuous cycle.

[0003] Currently, unpretreated compost material is directly used in the preparation of organic controlled-release fertilizer, the particle size of the material has large differences (there are often >5mm lumps or <0.1mm fine powder), the controlled-release agent is easy to agglomerate on the surface of the fine powder and is not completely covered on the surface of the lumps, resulting in large fluctuations in the nutrient release rate, and synthetic polymer controlled-release agents (such as PCL) are mostly used alone, although the controlled-release period is long (6-12 months), the cost is high (when the addition amount is 1%, the cost per ton increases by 200-300 yuan), and the biodegradability is poor, and at the same time, nutrient loss is serious during the preparation process, which reduces the effective nutrient content of the product, therefore, the method for preparing controlled-release fertilizer from organic material based on microbial fermentation is proposed. SUMMARY

[0004] The application aims to provide a method for preparing controlled-release fertilizer from organic material based on microbial fermentation, so as to solve the problems of the current organic controlled-release fertilizer preparation, such as directly using unpretreated compost material, large particle size difference of the material, easy agglomeration of the controlled-release agent on the surface of the fine powder, incomplete covering of the controlled-release agent on the surface of the lumps, large fluctuations in the nutrient release rate, and mostly single use of synthetic polymer controlled-release agents, although the controlled-release period is long, the cost is high, and the biodegradability is poor, and at the same time, nutrient loss is serious during the preparation process, which reduces the effective nutrient content of the product.

[0005] To achieve the above-mentioned purpose, the application provides the following technical scheme: a method for preparing controlled-release fertilizer from organic material based on microbial fermentation, comprising the following steps: S1, screening and proportioning the organic material; S2, crushing and conditioning the organic material after proportioning; S3, selecting and rejuvenating the microbial strains; S4, the rejuvenated microbial strain is expanded culture; S5, the microbial strain after expansion culture is inoculated and mixed with the organic material in S2; S6, the inoculated and mixed organic material in S5 is subjected to aerobic fermentation to obtain a mature organic material; S7, the mature organic material is pretreated and a controlled-release agent is added; S8, the granulation of the controlled-release fertilizer is formed; S9, the granulated controlled-release fertilizer is dried, cooled, screened and packaged; S10, the quality of the controlled-release fertilizer is detected.

[0006] Preferably, the organic material in S1 is selected, specifically: Stable source, rich in nutrients and easy to be decomposed by microorganisms, common types include livestock and poultry manure (such as chicken manure, cow dung, which needs to ensure no heavy metals exceed the standard, which can be detected by atomic absorption spectrophotometer to detect the content of lead, cadmium, mercury and other elements, in line with GB / T19524.1-2021 standard), agricultural waste (straw, rice husk, crushed to 2-5mm in size for easy microbial attachment), garden waste (dry branches and leaves, remove impurities such as stones and plastics and crush them), and kitchen waste.

[0007] Preferably, the organic material in S1 is mixed, specifically: The ratio is adjusted according to the carbon-nitrogen ratio (C / N) of different materials, and the goal is to control the C / N of the mixed material at 25:1-30:1, which is beneficial to the growth and reproduction of microorganisms. For example, when using straw with a higher C / N (about 80:1) and chicken manure with a lower C / N (about 15:1), the mass ratio of straw:chicken manure can be 3:2; if kitchen waste (C / N about 20:1) is added, the ratio of straw:chicken manure:kitchen waste can be adjusted to 2:2:1, and a blender is used to mix thoroughly to ensure uniformity.

[0008] Preferably, the organic material in S2 is crushed, specifically: Hammer crusher or shear crusher is used to crush blocky materials (such as cow dung, dry branches), and kneading crusher is used to crush long and thin materials such as straw and rice husk. The particle size of the crushed material is uniformly controlled at 2-5mm. If the particle size is too large, the contact area of the microorganisms is small and the fermentation efficiency is low; if the particle size is too small, the material is easy to clump and the aeration is poor.

[0009] Preferably, the organic material in S2 is conditioned, including moisture conditioning and pH conditioning Moisture conditioning: The moisture content of the mixture is tested by drying or moisture meter. If the moisture content is less than 50%, deionized water or composting liquid can be added to adjust the moisture content to 55%-60% (judgment criteria: the material can be formed into a ball when squeezed in the hand, water droplets can be seen between the fingers but not dripping, and it will disperse when dropped). If the moisture content is higher than 65%, dry sawdust or rice husk powder can be added to absorb excess moisture. pH adjustment: Use a pH meter to measure the pH value of the material. If the pH is lower than 6.0, add quicklime powder (0.5%-1% while stirring) to adjust it to 6.5-7.5. If the pH is higher than 8.0, add superphosphate (1%-2%) to adjust it, ensuring that the microorganisms are in a suitable acid-base environment.

[0010] Preferably, the microbial strains in S3 are revitalized, specifically by: Inoculate the bacterial strain into sterile LB medium (liquid, formulation: 10 g / L tryptone, 5 g / L yeast extract, 10 g / L sodium chloride, pH 7.0) and incubate at 30°C and 180 rpm for 24-36 hours, until the culture medium becomes turbid (OD600 value reaches 0.8-1.0, measured by UV spectrophotometer), ensuring that the bacterial strain has regained its activity. If using solid bacterial strain, a bacterial suspension (concentration 10) can be prepared by adding sterile water. 8 -10 9 CFU / mL, determined by plate count method.

[0011] Preferably, the microbial strain expansion culture in S4 includes primary expansion culture and secondary expansion culture; The specific steps of the primary scale-up culture are as follows: Inoculate the revitalized bacterial culture at a rate of 5%-10% into Erlenmeyer flasks containing solid culture medium (formula: 80% wheat bran, 15% corn flour, 3% sucrose, 2% yeast extract, with deionized water added to adjust the moisture content to 60%, autoclaved at 121℃ for 30 min). Incubate statically at 30℃ for 48-72 h, stirring every 24 h, until the surface of the medium is covered with mycelia or a large number of colonies appear. At this point, the viable count can reach 10^ ... 9 CFU / g or higher; The specific steps for the secondary expansion culture are as follows: Inoculate the primary culture at a rate of 10%-15% into the solid culture medium (same formula as primary culture, wheat bran can be replaced with some fermentation material to improve strain adaptability) in a fermenter (100-500L volume, pre-sterilized). Control the temperature at 30-32℃, the aeration rate at 0.5-1.0 vvm (volume air / volume culture medium / min), and the stirring rate at 50-80 r / min. Incubate for 72-96 hours, and monitor the viable count using the plate count method, reaching 10⁻⁶ cells / min. 10Stop culturing when CFU / g is reached, and use it as an inoculum.

[0012] Preferably, the inoculation and mixing in S5 specifically refers to: Mix the expanded cultured inoculum with a small amount of composted material to make an inoculum agent. Then, evenly sprinkle the inoculum agent into the pretreated organic material at an inoculation rate of 3%-5% of the total material. Use a turner or mixer to mix it thoroughly to ensure that the inoculum and material are mixed evenly and to avoid local inoculum concentrations being too high or too low. After inoculation, the material should be piled into trapezoidal or rectangular piles, with a height of 1.2-1.5m, a width of 2-3m, and a length depending on the site (generally not less than 5m). If the pile is too large, it will lead to insufficient internal ventilation; if it is too small, heat will easily dissipate. Cover the surface of the pile with a layer of breathable non-woven fabric or straw (5-10cm thick) to keep it warm and moist, while also preventing rainwater erosion.

[0013] Preferably, the pretreatment of the composted organic material in S7 specifically includes: The decomposed organic material is crushed in a hammer mill and then sieved through a 100-mesh standard sieve to remove incompletely decomposed lumps (which are then returned to the fermentation stage for re-fermentation), ensuring that the material has a uniform particle size for easy mixing with the controlled-release agent later.

[0014] Preferably, the controlled-release agent is added in step S7 as follows: Mix the selected controlled-release agent with the composted material in a certain proportion. If using a solid controlled-release agent (such as chitosan powder or bentonite), add it directly to the material and stir it for 20-30 minutes using a double helix mixer at a speed of 30-50 r / min to ensure uniform mixing. If using a liquid controlled-release agent (such as starch graft copolymer solution), spray it evenly onto the surface of the material using a spraying device while stirring. Continue stirring for 15-20 minutes after spraying to ensure that the controlled-release agent fully adheres to the surface of the material particles.

[0015] Compared with the prior art, the beneficial effects of the present invention are: (1) This application controls the particle size of the material uniformly within 0.5-2mm, eliminates the influence of particle size difference on the adhesion of the controlled-release agent, ensures uniform basic nutrients, and provides a stable material state for the adhesion and granulation of the controlled-release agent.

[0016] (2) This application uses an innovative composite controlled-release agent that combines the environmentally friendly degradation of natural polymers with the low-cost adsorption advantages of inorganic minerals. It is relatively simple in cost, can be completely degraded, and leaves no residue.

[0017] (3) This application optimizes temperature and time parameters, selects controlled-release agents suitable for low temperature, avoids damage to nutrients and organic matter by high temperature, and ensures that the effective nutrient content of the finished product meets the standards. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall method flow of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1 This invention provides a technical solution: a method for preparing controlled-release fertilizer from organic materials based on microbial fermentation, comprising the following steps: Step 1: First, screen and proportion the organic materials; Organic material screening: Select organic materials that are stable in origin, rich in nutrients, and easily decomposed by microorganisms. Common types include livestock and poultry manure (such as chicken manure and cow manure, which must be ensured to be free of heavy metals. The content of elements such as lead, cadmium, and mercury can be detected by atomic absorption spectrophotometer and meet the GB / T19524.1-2021 standard), agricultural waste (straw and rice husks, after crushing, the particle size is controlled to be 2-5mm to facilitate microbial attachment), garden waste (fallen branches and leaves, after removing impurities such as stones and plastics, and then crushing), and kitchen waste.

[0021] Organic material ratio: Adjust the ratio according to the carbon-to-nitrogen ratio (C / N) of different materials, aiming to control the C / N ratio of the mixture at 25:1-30:1, which is conducive to the growth and reproduction of microorganisms. For example, when using straw with a high C / N ratio (about 80:1) and chicken manure with a low C / N ratio (about 15:1), the mass ratio of straw:chicken manure = 3:2 can be mixed; if kitchen waste (C / N about 20:1) is added, the ratio can be adjusted to straw:chicken manure:kitchen waste = 2:2:1. Use a mixer to mix thoroughly during the mixing process to ensure that the materials are uniform.

[0022] Taking "binary material mixing" as an example: When using only two materials with a large difference in C / N ratio (such as straw with a high C / N ratio and chicken manure with a low C / N ratio), calculate the ratio according to the following steps: Step 1: Define variables and objectives Let the mass of a high C / N material (such as straw) be X kg, and its C / N be C1 / N1 (e.g., straw C / N=80:1, that is, C1=80, N1=1). The mass of low C / N material (such as chicken manure) is Y kg, and its C / N is C2 / N2 (such as chicken manure C / N=15:1, that is, C2=15, N2=1). Target: X + Y = total mass (e.g., 100 kg), and (X × C1 + Y × C2) / (X × N1 + Y × N2) = target C / N (e.g., 28:1). Step 2: Substitute the values ​​into the formula to calculate the material mass. Based on the above objectives, the formula for the proportioning of binary materials is derived as follows: X = [Y × (target C / N × N2 - C2)] / (C1 - target C / N × N1) Combining "X + Y = total mass", substitute the numerical values ​​for calculation: Case: Total mass 100kg, using straw (C / N=80:1) and chicken manure (C / N=15:1), target C / N=28:1 Substitute into the formula: Given that the target C / N = 28, C1 = 80, N1 = 1; C2 = 15, N2 = 1; X + Y = 100 kg; Then X = [Y × (28 × 1 - 15)] / (80 - 28 × 1) = (13Y) / 52 = Y / 4; Combined with total mass: X+Y=Y / 4+Y=5Y / 4=100kg→Y=80kg, X=20kg; verify: Total carbon content of the mixture = 20kg × 80 (carbon percentage of straw, since C / N = 80:1, that is, 1 part nitrogen corresponds to 80 parts carbon, the calculation can be simplified) + 80kg × 15 (carbon percentage of chicken manure) = 1600 + 1200 = 2800; Total nitrogen content of the mixture = 20kg × 1 + 80kg × 1 = 100 The actual C / N ratio is 2800 / 100 = 28:1, which meets the target. Step 3: Hands-on mixing and fine-tuning Weigh the materials according to the calculation results (e.g., 20kg of straw and 80kg of chicken manure), and first crush the straw to 2-5mm (to increase the contact area with the chicken manure). Mix the two materials in a mixer for 10-15 minutes to ensure even distribution. After mixing, take samples to test the actual C / N ratio (if laboratory conditions are limited, a preliminary judgment can be made by "feel + smell": if the material has no obvious pungent smell and is loose and does not clump when squeezed, it indicates that the ratio is basically reasonable; if the material is too dry and easily generates dust, there may be too much high C / N material, and low C / N material needs to be added; if the material is too wet and has a foul smell, there may be too much low C / N material, and high C / N material needs to be added).

[0023] Step 2: Crush and process the prepared organic materials; Organic materials are crushed: Hammer mills or shear mills are used to crush lumpy materials (such as cow dung and dead branches). Straw, rice husks and other slender materials can be processed by a kneading mill. The particle size of the crushed material should be uniformly controlled at 2-5mm. If the particle size is too large, the contact area of ​​microorganisms is small and the fermentation efficiency is low; if the particle size is too small, the material is prone to clumping and poor aeration.

[0024] Conditioning of organic materials includes moisture conditioning and pH adjustment; Moisture conditioning: Use a drying method or a moisture meter to test the moisture content of the mixture. If the moisture content is less than 50%, deionized water or composting liquid can be added to adjust the moisture content to 55%-60% (judgment criteria: the material can be formed into a ball when squeezed in the hand, water droplets can be seen between the fingers but not dripping, and it will disperse when dropped). If the moisture content is higher than 65%, dry sawdust or rice husk powder can be added to absorb excess moisture. pH Adjustment: Use a pH meter to measure the pH value of the material. If the pH is below 6.0, add quicklime powder (0.5%-1%, stirring continuously) to adjust it to 6.5-7.5; if the pH is above 8.0, add superphosphate (1%-2%) to ensure that the microorganisms are in a suitable acid-base environment. Step 3: Select and rejuvenate microbial strains; Microbial strain selection: Based on the fermentation objectives, select a high-efficiency compound microbial strain. Core strains include *Trichoderma reesei* (decomposes cellulose), *Bacillus subtilis* (decomposes proteins), actinomycetes that promote humus formation (such as *Streptomyces*), and nitrogen-fixing bacteria (such as *Azotobacter chroococcum*). The strain ratio can be a mixture of *Trichoderma reesei*: *Bacillus subtilis*: actinomycetes: nitrogen-fixing bacteria = 2:3:3:2. Alternatively, commercially available compound microbial agents specifically for organic material composting can be used (must meet NY / T798-2021 standards, with an effective viable count ≥ 200 million / g). Microbial strain revitalization: Inoculate the strain into sterile LB medium (liquid, formulation: 10 g / L tryptone, 5 g / L yeast extract, 10 g / L sodium chloride, pH 7.0), and incubate at 30°C and 180 rpm for 24-36 hours until the culture medium becomes turbid (OD600 value reaches 0.8-1.0, measured by UV spectrophotometer), ensuring the strain has regained its activity; if using solid strains, a bacterial suspension (concentration 10) can be prepared by adding sterile water. 8 -10 9 (CFU / mL, determined by plate count method); Step 4: Expand the culture of the rejuvenated microbial strains; Microbial strain expansion culture includes primary expansion culture and secondary expansion culture; The specific steps for primary expansion culture are as follows: Inoculate the revitalized bacterial culture at a rate of 5%-10% into Erlenmeyer flasks containing solid culture medium (formula: 80% wheat bran, 15% corn flour, 3% sucrose, 2% yeast extract, with deionized water added to adjust the moisture content to 60%, autoclaved at 121℃ for 30 min). Incubate statically at 30℃ for 48-72 h, stirring every 24 h, until the surface of the medium is covered with mycelia or a large number of colonies appear. At this point, the viable count can reach 10^ ... 9 CFU / g or higher; The specific steps for secondary expanded culture are as follows: Inoculate the primary culture at a rate of 10%-15% into the solid culture medium (same formula as primary culture, wheat bran can be replaced with some fermentation material to improve strain adaptability) in a fermenter (100-500L volume, pre-sterilized). Control the temperature at 30-32℃, the aeration rate at 0.5-1.0 vvm (volume air / volume culture medium / min), and the stirring rate at 50-80 r / min. Incubate for 72-96 hours, and monitor the viable count using the plate count method, reaching 10⁻⁶ cells / min. 10 Stop culturing when CFU / g is reached, and use it as an inoculum.

[0025] Step 5: Inoculate and mix the expanded microbial strains with the organic materials from Step 2; Inoculation and mixing: Mix the expanded cultured strain with a small amount of decomposed material to make a strain inoculum. Then, evenly sprinkle the inoculum into the pretreated organic material at an inoculation rate of 3%-5% of the total material. Use a turner or mixer to mix thoroughly to ensure that the strain and material are mixed evenly and to avoid local strain concentrations that are too high or too low. After inoculation, the material should be piled into trapezoidal or rectangular piles, with a height of 1.2-1.5m, a width of 2-3m, and a length depending on the site (generally not less than 5m). If the pile is too large, it will lead to insufficient internal ventilation; if it is too small, heat will easily dissipate. Cover the surface of the pile with a layer of breathable non-woven fabric or straw (5-10cm thick) to keep it warm and moist, while also preventing rainwater erosion.

[0026] Step 6: Perform aerobic fermentation on the inoculated and mixed organic materials from Step 5 to obtain decomposed organic materials; Temperature monitoring: Thermometers were inserted at different locations in the pile (30cm below the surface, middle layer, and bottom layer, with 3 monitoring points at each location), and the temperature was recorded at 9:00 AM and 3:00 PM daily. In the early stage of fermentation (0-3 days), the temperature gradually rises to below 50℃, which is the mesophilic stage, mainly characterized by mesophilic microbial activity. From 3 to 7 days, the temperature enters the high-temperature stage, rising to 55-65℃. At this time, thermophilic microorganisms (such as Bacillus and Actinomycetes) multiply in large numbers, killing pathogens, insect eggs, and weed seeds in the material (high temperature must be maintained for more than 5 days to ensure sterilization effect). After 7 days, the temperature gradually decreases to below 50℃, entering the cooling stage. At this time, microorganisms begin to decompose recalcitrant organic matter, forming humus. Turning operation: When the pile temperature exceeds 65℃, it is necessary to turn the pile in time to avoid the high temperature inhibiting the activity of microorganisms. During the high temperature stage, turn the pile every 2-3 days, and during the cooling stage, turn the pile every 3-5 days. When turning the pile, use a turner to fully mix the materials on the top and bottom and inside and outside of the pile to improve ventilation, replenish oxygen, and adjust the moisture content of the pile (if the moisture content is less than 50%, an appropriate amount of water can be sprayed during turning). Ventilation and Moisture Control: Ventilation Control: In addition to turning the pile, ventilation pipes can be laid at the bottom of the pile (1-1.5m spacing, with holes drilled in the pipes, 5-8mm in diameter) to introduce air (the ventilation rate is adjusted according to the size of the pile, generally 0.1-0.3m³ / (m³・h)) to ensure that the oxygen content of the pile is not less than 10% (use an oxygen detector to monitor; if it is less than 8%, the ventilation rate or turning frequency needs to be increased). Moisture control: Regularly monitor the moisture content during fermentation. If the moisture content is below 50% due to evaporation, spray deionized water evenly during turning to maintain the moisture content at 55%-60%. If the moisture content is above 65% due to rainwater or water produced by the fermentation of the material itself, increase the frequency of turning and strengthen ventilation to promote moisture evaporation.

[0027] Fermentation endpoint determination: Fermentation for 15-25 days (the specific time is adjusted according to the type of material and ambient temperature). When the temperature of the pile drops to ±2℃ of the ambient temperature, the material color turns dark brown or black, there is no odor (but there is a fresh earthy fragrance), the texture is loose, it is easy to break when held in the hand, and a large number of humic particles are observed under a microscope. At this time, fermentation is complete and mature organic material is obtained.

[0028] Step 7: Pre-treat the composted organic materials and add controlled-release agents; Pretreatment of composted organic materials: The composted organic materials are crushed in a hammer mill and then sieved through a 100-mesh standard sieve to remove incompletely composted lumps (which are returned to the fermentation stage for re-fermentation) to ensure uniform particle size and facilitate subsequent mixing with controlled-release agents.

[0029] Adding controlled-release agent: Mix the selected controlled-release agent with the composted material in proportion. If using a solid controlled-release agent (such as chitosan powder or bentonite), add it directly to the material and stir for 20-30 minutes using a twin-helix mixer at a speed of 30-50 r / min to ensure uniform mixing. If using a liquid controlled-release agent (such as starch graft copolymer solution), spray it evenly onto the surface of the material using a spraying device while stirring. Continue stirring for 15-20 minutes after spraying to ensure that the controlled-release agent fully adheres to the surface of the material particles.

[0030] Step 8: Granulate and shape the controlled-release fertilizer; Granulation operation: Disc granulator: Feed the prepared material into the disc granulator (disc diameter 1.5-2.0m, inclination angle 45°-50°, rotation speed 15-20r / min), start the equipment, the material rolls in the disc to form granules, and control the particle size (target particle size 2-4mm) by adjusting the feed rate and the disc rotation speed. Unqualified small particles (<2mm) are returned to the granulator for regranulation, and large particles (>4mm) are crushed and reused. Extrusion granulator: The material is fed into the feed inlet of the extrusion granulator, and the material is extruded into strips by the screw extrusion device. Then, it is cut into granules by the cutter (the particle size can be adjusted by the speed of the cutter). The granules enter the subsequent drying process.

[0031] Step 9: Dry, cool, screen, and package the granulated controlled-release fertilizer; Drying process: The granulated wet granules are fed into a drum dryer (inlet temperature 120-140℃, outlet temperature 50-60℃, rotation speed 10-15 r / min) for 30-60 minutes to reduce the moisture content of the granules to below 10% (as measured by a moisture analyzer) to prevent mold and deterioration during storage. Temperature must be controlled during the drying process to prevent nutrient loss (such as urea decomposition) due to excessively high temperatures. Cooling treatment: The dried granules are at a high temperature (50-60℃) and need to be sent to a cooler (using air cooling, wind speed 3-5m / s) to cool to room temperature (temperature difference ≤5℃ from the ambient temperature) to avoid the accumulation of high-temperature granules and agglomeration, and at the same time facilitate subsequent screening and packaging. Screening: The cooled granules are screened through grading sieves (sieve mesh size 2mm and 4mm) to obtain qualified products with a particle size of 2-4mm. The fine powder (<2mm) that is screened off is returned to the granulation process, while the large particles (>4mm) that are screened off are sent to a pulverizer for crushing and reuse to ensure that the product has a uniform particle size. Packaging: Double-layer packaging is used. The inner layer is a polyethylene film bag (to prevent moisture intrusion), and the outer layer is a woven bag. Packaging specifications can be set according to market demand (e.g., 25kg / bag, 50kg / bag). Before packaging, the product name, nutrient content (N-P2O5-K2O), organic matter content, controlled-release period, production date, shelf life, and manufacturer information must be labeled on the packaging bag, complying with the requirements of GB18877-2021 "Organic-Inorganic Compound Fertilizers" standard.

[0032] Step 10: Conduct quality testing on the controlled-release fertilizer; Nutrient content: Measure the content of total nitrogen, available phosphorus, and available potassium (using the same method as the nutrient testing of composted materials) to ensure that the total nutrient content meets the design requirements and that the proportion of controlled-release nutrients (e.g., controlled-release nitrogen accounts for more than 30% of the total nitrogen, adjusted according to product positioning) meets the controlled-release fertilizer standard (e.g., GB / T23348-2020 "Slow-Release Fertilizers"). Organic matter content: determined by potassium dichromate oxidation-external heating method, must be ≥30%; Moisture content: determined by drying method, ≤10%; pH value: determined by water extraction-pH meter method, controlled between 6.0 and 8.0; Particle size: determined by sieving method, with particles of 2-4 mm accounting for ≥90%. Controlled-release performance testing: Nutrient release rate is determined by water leaching or soil culture. For example, at 25°C, the controlled-release fertilizer sample is placed in deionized water (liquid-solid ratio 50:1), and samples are taken periodically (1 day, 7 days, 14 days, 30 days, 60 days, and 90 days) to determine the nitrogen, phosphorus, and potassium content in the solution and plot the nutrient release curve. The cumulative nutrient release rate is required to meet the design requirements within the controlled-release period (e.g., 3 months and 6 months) (e.g., cumulative release rate ≤60% within 3 months and ≥80% within 6 months). Safety testing: The content of heavy metals (lead, cadmium, mercury, chromium, arsenic) is tested (atomic absorption spectrophotometer or inductively coupled plasma mass spectrometry), which meets the limits of GB18877-2021 standard; the mortality rate of Ascaris eggs (≥95%) and the number of fecal coliforms (≤100 CFU / g) are tested, which meet the standards of NY / T798-2021, ensuring that the product is safe and harmless.

[0033] In summary: 1. Through a pretreatment process of coarse crushing → fine crushing → double-layer screening, the particle size of the material is uniformly controlled at 0.5-2mm (with a qualified rate of ≥90%), eliminating the influence of particle size differences on the adhesion of the controlled-release agent; the material nutrients are first tested and inorganic nutrients (such as urea and superphosphate) are added as needed to ensure uniform basic nutrients; then the moisture content is adjusted to 18%-22% (it can be formed into a ball when squeezed by hand, but easily dispersed when lightly touched), providing a stable material state for the adhesion and granulation of the controlled-release agent, and increasing the qualified rate of the finished product to over 95%.

[0034] 2. Using innovative composite controlled-release agents (such as chitosan + bentonite = 1:3), combining the "environmentally friendly degradation" of natural polymers with the "low-cost adsorption" advantages of inorganic minerals, the controlled-release cycle reaches 4-8 months, the cost is reduced by 40%-50% compared to single synthetic polymers, and it can be completely degraded in soil in 6-8 months without residue.

[0035] 3. Optimize temperature and time parameters: When adding urea, the inlet air temperature of fluidized bed granulation should be ≤65℃, the extrusion granulation temperature should be ≤60℃, the solidification time of liquid controlled release agent should be shortened to 10-15min (50-60℃ hot air), and the nitrogen volatilization loss rate should be controlled within 5%. Choose a low-temperature-compatible controlled-release agent (such as starch graft copolymer, curing temperature 40-50℃) to avoid the damage of nutrients and organic matter caused by high temperature, and ensure that the effective nutrient content of the finished product meets the standard (such as N-P2O5-K2O=8-5-7, error ≤5%).

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing controlled-release fertilizer from organic materials based on microbial fermentation, characterized in that, Includes the following steps: S1. First, the organic materials are screened and proportioned. S2. Crush and condition the proportioned organic materials; S3. Selection and rejuvenation of microbial strains; S4. Expand the culture of the rejuvenated microbial strains; S5. Inoculate and mix the expanded cultured microbial strains with the organic materials in S2; S6. The organic material inoculated and mixed in S5 is subjected to aerobic fermentation to obtain decomposed organic material. S7. Pre-treatment of mature organic materials, and addition of controlled-release agents; S8. Granulation and molding of controlled-release fertilizer; S9. The granulated controlled-release fertilizer is dried, cooled, screened, and packaged. S10. Conduct quality testing on controlled-release fertilizers.

2. The method for preparing controlled-release fertilizer from organic materials based on microbial fermentation according to claim 1, characterized in that, The organic material screening in S1 specifically involves: Select organic materials that are stable in origin, rich in nutrients, and easily decomposed by microorganisms. Common types include livestock and poultry manure, agricultural waste, garden waste, and kitchen waste.

3. The method for preparing controlled-release fertilizer from organic materials based on microbial fermentation according to claim 1, characterized in that, The specific proportions of organic materials in S1 are as follows: Adjust the ratio of carbon to nitrogen (C / N) of different materials to control the C / N ratio of the mixture at 25:1-30:1, which is conducive to the growth and reproduction of microorganisms.

4. The method for preparing controlled-release fertilizer from organic materials based on microbial fermentation according to claim 1, characterized in that, The organic material in S2 is pulverized, specifically as follows: Hammer mills or shear mills are used to crush lumpy materials. Slender materials such as straw and rice husks can be processed by kneading mills. The particle size of the crushed materials is uniformly controlled between 0.5-2mm.

5. The method for preparing controlled-release fertilizer from organic materials based on microbial fermentation according to claim 1, characterized in that, The conditioning of organic materials in S2 includes moisture conditioning and pH conditioning. Moisture conditioning: The moisture content of the mixture is detected by drying or moisture meter. If the moisture content is less than 50%, deionized water or composting liquid is added to adjust the moisture content to 55%-60%. If the moisture content is higher than 65%, dry sawdust or rice husk powder is added to absorb excess moisture. pH adjustment: Use a pH meter to measure the pH value of the material. If the pH is below 6.0, add quicklime powder to adjust it to 6.5-7.5; if the pH is above 8.0, add superphosphate to adjust it.

6. The method for preparing controlled-release fertilizer from organic materials based on microbial fermentation according to claim 1, characterized in that, The microbial strains in S3 are rejuvenated, specifically as follows: Inoculate the bacterial strain into sterile LB medium and incubate at 30°C and 180 rpm for 24-36 hours until the culture medium becomes turbid.

7. The method for preparing controlled-release fertilizer from organic materials based on microbial fermentation according to claim 1, characterized in that, The microbial strain expansion culture in S4 includes primary expansion culture and secondary expansion culture; The specific steps for the primary scale-up culture are as follows: Inoculate the revitalized bacterial culture into Erlenmeyer flasks containing solid culture medium at an inoculation rate of 5%-10%. Incubate at 30°C for 48-72 hours, stirring every 24 hours, until the surface of the medium is covered with mycelia or a large number of colonies appear. At this point, the viable count can reach 10^10^6 cells / mL. 9 CFU / g or higher; The specific steps for the secondary expansion culture are as follows: Inoculate the primary culture into the solid culture medium in the fermenter at an inoculum rate of 10%-15%, control the temperature at 30-32℃, the aeration rate at 0.5-1.0 vvm, the stirring rate at 50-80 r / min, and incubate for 72-96 h. Monitor the viable cell count using the plate count method, and check if it reaches 10⁻⁶. 10 Stop culturing when CFU / g is reached, and use it as an inoculum.

8. The method for preparing controlled-release fertilizer from organic materials based on microbial fermentation according to claim 1, characterized in that, The inoculation and mixing in S5 are specifically as follows: Mix the expanded cultured inoculum with a small amount of composted material to make an inoculum agent. Then, evenly sprinkle the inoculum agent into the pretreated organic material at an inoculation rate of 3%-5% of the total material. Use a turner or mixer to mix it thoroughly to ensure that the inoculum and material are mixed evenly and to avoid local inoculum concentrations being too high or too low. After inoculation, the material is piled into a trapezoidal or rectangular pile, and the surface of the pile is covered with a layer of breathable non-woven fabric or straw.

9. The method for preparing controlled-release fertilizer from organic materials based on microbial fermentation according to claim 1, characterized in that, The pretreatment of the decomposed organic material in S7 specifically includes: The well-rotted organic materials are crushed in a hammer mill and then sieved through a 100-mesh standard sieve to remove incompletely decomposed lumpy materials.

10. The method for preparing controlled-release fertilizer from organic materials based on microbial fermentation according to claim 1, characterized in that, The controlled-release agent added in S7 is specifically as follows: Mix the selected controlled-release agent with the composted material in a certain proportion, and stir for 20-30 minutes using a double-helix mixer at a speed of 30-50 r / min to ensure uniform mixing; or spray evenly onto the surface of the material using a spraying device while stirring, and continue stirring for 15-20 minutes after spraying to ensure that the controlled-release agent fully adheres to the surface of the material particles.

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