A method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw

Abstract

The application discloses a method for preparing organic fertilizer by crop straw enzymolysis and fermentation, and belongs to the technical field of straw resource utilization. The method comprises the following steps: firstly, crushing the straw, and then performing steam explosion and far infrared radiation cooperative pretreatment; secondly, mixing the nitrogen source auxiliary material, humic acid composite raw material and mineral additive to prepare fermentation base material; thirdly, adding the composite enzyme preparation, polyethylene glycol and distilled water to the base material for segmented constant-temperature enzymolysis, and then adding the composite microbial inoculum and auxiliary additive to obtain a fermentation product; and finally, performing segmented fermentation on the product, adding bentonite and low-temperature drying to obtain a finished product. The method can shorten the fermentation period by optimizing the process, reducing the crystallinity of straw cellulose to 18-25%, and degrading the straw at a rate of more than 80%. The organic fertilizer has an organic matter content of greater than or equal to 60%, a total nutrient content of N+P2O5+K2O of greater than or equal to 5%, and a high total humic acid content, and can improve the physicochemical properties of soil, and realizes efficient and environment-friendly resource utilization of the straw.

Description

Technical Field

[0001] This invention belongs to the field of straw enzymatic hydrolysis and fermentation technology, and relates to a method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw. Background Technology

[0002] my country produces nearly 1 billion tons of crop straw annually, with over 700 million tons available for collection. Major straw types, such as corn stalks, wheat stalks, and rice stalks, account for over 80% of this. As an important byproduct of agricultural production, straw is rich in cellulose (30-45%), hemicellulose (20-30%), lignin (15-25%), and natural nutrients such as nitrogen, phosphorus, and potassium. It has high resource utilization value and is an important renewable raw material for producing organic fertilizer. Its efficient conversion and utilization not only align with the development direction of green agricultural transformation and industrial upgrading but also meet the strategic requirements of promoting resource recycling and green, low-carbon development.

[0003] However, the overall level of straw resource utilization in my country remains low, especially in the field of enzymatic fermentation for organic fertilizer production. Existing technologies still face numerous bottlenecks, hindering the high-value conversion and large-scale application of straw resources. Traditional straw treatment methods include direct burning, which easily causes air pollution and contradicts the "dual carbon" strategic goal; simple composting fermentation suffers from long cycles, insufficient degradation of lignocellulose, low nutrient conversion efficiency, and unstable fertilizer effects. Meanwhile, existing enzymatic fermentation technologies generally suffer from insufficient enzymatic efficiency, susceptibility of microbial activity to environmental influences, and difficulty in precisely controlling the fermentation process. Some processes also require the addition of chemical reagents, posing a risk of secondary pollution.

[0004] Furthermore, the current utilization rate of straw resources is generally below 60%, with a large amount of resources failing to be effectively converted, resulting in significant waste and failing to fully realize the important strategic value of straw in replacing imported chemical raw materials and enhancing the resilience of the agricultural industry chain. Existing technologies mostly employ a combination of enzyme preparations and microbial communities, but the synergistic mechanism between the two has not been fully realized. Simultaneously, the fermentation process lacks systematic control over key parameters such as temperature, humidity, and carbon-nitrogen ratio, leading to significant fluctuations in core indicators of the finished organic fertilizer, such as microbial activity and humic acid content, making it difficult to meet the demands of modern agriculture for high-quality organic fertilizer.

[0005] Therefore, developing an efficient, environmentally friendly, and highly controllable enzymatic fermentation method for preparing organic fertilizer that enables the high-value utilization of straw resources has significant practical significance and broad application prospects. Summary of the Invention

[0006] To address the aforementioned technical shortcomings, particularly the low nutrient conversion efficiency, unstable microbial activity, and insufficient enzyme-microbe synergy, this invention proposes a method for preparing organic fertilizer through enzymatic hydrolysis and fermentation of crop straw.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw, characterized by comprising the following steps: S1. Select straw as raw material, remove impurities such as stones and weeds, and then crush it with a crusher to obtain pre-treated straw. S2. Mix the pretreated straw, nitrogen source material, humic acid composite material and mineral additives evenly in a mass ratio of (60~70):(15~25):(5~10):(3~8) to obtain the fermentation base material; S3. Add the compound enzyme preparation to the fermentation substrate in sequence to obtain the fermentation substrate mixture, then add distilled water, stir evenly and then enzymatically hydrolyze; the mass ratio of the fermentation substrate mixture to distilled water is 1:(1.8~2); S4. After enzymatic hydrolysis, add compound microbial agent and auxiliary additives in sequence to obtain fermentation product; the mass fraction of compound microbial agent is 0.5~1.5%, and the mass ratio of compound microorganism to auxiliary additive is 1:(8~15). S5. Place the fermentation product in an aerobic fermentation device. After fermentation, cool it to room temperature, sieve and remove impurities, add 0.5-1% bentonite by mass, and dry it at a low temperature of 60-80℃ to obtain the finished organic fertilizer.

[0008] Preferably, the straw in step S1 is at least one of corn stalks, wheat straw, rice straw, and sorghum straw.

[0009] Preferably, the crushed straw is subjected to a combination of steam explosion and far-infrared radiation treatment. The steam explosion process parameters are: pressure 0.9~1.1MPa, time 40~90s, and temperature 130~160℃; the far-infrared radiation has a wavelength of 9~12μm, a power of 600~700W, and a time of 25~35min.

[0010] Preferably, an inert gas is intermittently introduced during the far-infrared radiation process. The inert gas can be any one of nitrogen, argon, or helium, with a flow rate of 0.5~1L / min.

[0011] Preferably, the humic acid composite raw material in step S2 is prepared by compounding weathered coal, lignite and biochar in a mass ratio of (1.5~3):(0.5~2):(0.3~0.8); the nitrogen source auxiliary material is any one of soybean meal, peanut meal, rapeseed meal and soybean protein residue; the mineral additive is prepared by compounding phosphate rock powder, potassium feldspar and zeolite powder in a mass ratio of (2~3):(1~2):1.

[0012] Preferably, the biochar is activated at 800-900℃, and the activated biochar has a specific surface area ≥300m².2 / g.

[0013] Preferably, the mass fraction of the composite enzyme in step S3 is 0.3-0.8%; the composite enzyme is prepared by compounding cellulase, xylanase, and protease / mannanase in a mass ratio of 3-4:2-3:1-2; and 0.2-0.5% of polyethylene glycol 600 is added to the composite enzyme.

[0014] Preferably, the compound microbial agent in step S4 is composed of Bacillus, Trichoderma, and yeast, with a mass ratio of (2~3):(1~2):(1~1.5); the auxiliary additive is a compound of sodium alginate, xylooligosaccharide, and chitosan oligosaccharide, with a mass ratio of (0.5~2):(0.3~0.8):(0.2~0.5); the Bacillus is at least one of Bacillus subtilis, Bacillus licheniformis, and Bacillus spathulatus; the Trichoderma is at least one of Trichoderma viride and Trichoderma thermophilum; and the yeast is at least one of Saccharomyces cerevisiae and Rhodotorula rubra.

[0015] Preferably, a gradient temperature is used in the enzymatic hydrolysis stage: the initial fermentation temperature is 45~48℃ and the time is 2~2.5h; the middle fermentation temperature is 50~52℃ and the time is 1.5~2h; the late fermentation temperature is 53~55℃ and the time is 0.5~1h; and citric acid is used to adjust the pH to 5.8~6.2.

[0016] Preferably, the fermentation stage is carried out in stages. The initial fermentation temperature is 50-55℃ and the time is 5-7 days, with ventilation twice a day and an oxygen content of 18-22%. The later fermentation temperature is 55-65℃ and the time is 3-5 days, with ventilation once a day and an oxygen content of 15-18%.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention significantly improves the efficiency and quality of straw enzymatic fermentation for organic fertilizer production through multi-stage process optimization and synergistic innovation. In the straw pretreatment stage, steam explosion and far-infrared radiation are used in synergistic treatment, reducing cellulose crystallinity to 18-25%. In the enzymatic hydrolysis stage, a multi-enzyme synergistic system is constructed, increasing the straw degradation rate to over 80% and shortening the hydrolysis time to 4-6 hours. In the fermentation stage, segmented temperature control is used to shorten the fermentation cycle, with the high-temperature period lasting ≥3 days, effectively killing pathogens and harmful microorganisms and ensuring a stable and odorless fermentation system.

[0018] 2. The reaction system of this invention avoids the use of highly polluting chemical reagents. The straw pretreatment relies on physical treatment methods and does not introduce any chemical modifiers. Natural compound enzyme preparations, microbial agents and green auxiliary additives are added during the enzymatic hydrolysis and fermentation process, and no chemical residues are generated, which ensures soil safety and crop quality after the application of organic fertilizer, highlighting the environmental innovation and sustainability of the process design.

[0019] 3. Through precise proportioning and parameter control of each component of the fermentation base, the finished organic fertilizer has an organic matter content of ≥60%, total N+P2O5+K2O nutrients of ≥5%, total humic acid of ≥16.2%, and the total heavy metal content is controlled at a low level of 102.2~116.5mg / kg. It has both fertilizer effect and soil improvement function, and truly realizes the high-value and environmentally friendly utilization of straw resources. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] To achieve the above-mentioned objectives of the present invention, the technical solution of the present invention will be further described in detail below, but the scope of protection of the present invention is not limited to the following description.

[0022] A method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw includes the following steps: S1. Select one or two types of corn, wheat, and sorghum straw as raw materials. After removing impurities such as stones and weeds, crush the straw into 2-5 cm pieces using a pulverizer. The crushed straw is then subjected to a combined treatment of steam explosion and far-infrared radiation. After steam explosion, far-infrared radiation is performed after an interval of 5-10 minutes to obtain pretreated straw. The steam explosion process parameters are: pressure 0.9-1.1 MPa, time 40-90 s, and temperature 130-160℃. The far-infrared radiation has a wavelength of 9-12 μm, a power of 600-700 W, and a time of 25-35 minutes. During the radiation process, an inert gas is intermittently introduced. The inert gas is any one of nitrogen, argon, and helium, with a flow rate of 0.5-1 L / min.

[0023] S2. Pretreated straw, nitrogen source material, humic acid composite material, and mineral additives are mixed evenly at a mass ratio of 60-70:15-25:5-10:3-8 to obtain a fermentation base material, with the carbon-to-nitrogen ratio controlled at 25-30:1. The nitrogen source material is any one of soybean meal, peanut meal, rapeseed meal, or soybean protein residue. The mineral additives are prepared by compounding phosphate rock powder, potassium feldspar, and zeolite powder at a mass ratio of (2-3):(1-2):(0.5-1). The humic acid composite material is prepared by compounding weathered coal, lignite, and activated biochar at a mass ratio of (1.5-3):(0.5-2):(0.3-0.8), with a particle size of 60-80 mesh. The biochar is activated at 800-900℃, and the specific surface area after activation is ≥300 m². 2 / g; S3. Add 0.3-0.8% by mass of a compound enzyme preparation and 0.2-0.5% by mass of polyethylene glycol 600 (purity ≥99.5%) to the fermentation substrate in step S2 to obtain a fermentation substrate mixture. Then add distilled water, stir evenly, and enzymatically hydrolyze at a constant temperature. The compound enzyme preparation is prepared by compounding cellulase, xylanase, and protease / mannanase in a mass ratio of (3-4):(2-3):(1-2). The mass ratio of the fermentation substrate mixture to distilled water is 1:(1.8-2). S4. After enzymatic hydrolysis, add the compound microbial agent and auxiliary additives sequentially, stir evenly, and perform segmented gradient temperature enzymatic hydrolysis to obtain the fermentation product; the mass fraction of the compound microbial agent is 0.5~1.5%, and the mass ratio of the compound microorganisms to the auxiliary additives is 1:(8~15); the compound microbial agent is composed of Bacillus, Trichoderma, and yeast, with a mass ratio of (2~3):(1~2):(1~1.5); the Bacillus is at least one of Bacillus subtilis, Bacillus licheniformis, and Bacillus spatholobus; the Trichoderma is at least one of Trichoderma viride and Trichoderma thermophilum; the yeast is at least one of Saccharomyces cerevisiae and Rhodotorula rubra; wherein, the effective viable count of Bacillus is ≥2.5x10⁻¹⁰. 6 CFU / g, cultured on LB medium at 30-37℃ for 24 h; Trichoderma viable count ≥1x10⁻⁶ 7 CFU / g, cultured on PDA medium at 25-28℃ for 72 h, with a spore germination rate ≥90% as the effective counting standard; effective viable yeast count ≥2.5 x 10⁻⁶. 5The concentration was CFU / g, and the culture was carried out in YPD medium at 28-30℃ for 36 hours. The auxiliary additives were a mixture of sodium alginate, xylooligosaccharide, and chitosan oligosaccharide in a mass ratio of (0.5-2):(0.3-0.8):(0.2-0.5). The gradient temperature enzymatic hydrolysis was divided into three parts: the initial fermentation temperature was 45-48℃ for 2-2.5 hours; the middle fermentation temperature was 50-52℃ for 1.5-2 hours; and the final fermentation temperature was 53-55℃ for 0.5-1 hour. The pH was monitored every 30 minutes, and the pH was adjusted to 5.8-6.2 with citric acid. S5. Place the fermentation product in an aerobic fermentation device and adopt segmented fermentation. The entire fermentation process is covered with a breathable nano-membrane. After fermentation, cool to room temperature, sieve through a 10-20 mesh sieve to remove impurities, add 0.5-1% bentonite by mass, dry at a low temperature of 60-80℃, and stir evenly to obtain the finished organic fertilizer. The segmented fermentation is divided into an early stage and a late stage. The early stage fermentation temperature is 50-55℃, the fermentation time is 5-7 days, ventilation is carried out twice a day, and the oxygen content is 18-22%. The late stage fermentation temperature is 55-65℃, the fermentation time is 3-5 days, ventilation is carried out once a day, and the oxygen content is 15-18%.

[0024] Example 1 S1. Select corn stalks and wheat stalks and mix them at a mass ratio of 1.5:1. After removing impurities, crush them into 3cm pieces. The crushed stalks are then subjected to steam explosion, and far-infrared radiation is performed after an 8-minute interval to obtain pretreated stalks. The steam explosion parameters are: pressure 1.0MPa, time 60s, temperature 150℃, wavelength 10μm, power 650W, and time 30min. Nitrogen gas is intermittently introduced during the radiation process at a flow rate of 0.8L / min. S2. Pretreated straw, soybean meal, humic acid composite raw material and mineral additives are mixed in a mass ratio of 65:20:8:5 to obtain fermentation base material with a carbon-nitrogen ratio of 25:1. The mineral additives are prepared by compounding phosphate rock powder, potassium feldspar and zeolite powder in a mass ratio of 2.5:1.5:1. The humic acid composite raw material is prepared by compounding weathered coal, lignite and activated biochar in a mass ratio of 2:1:0.5 with a particle size of 70 mesh. The biochar is activated at 850℃ and has a specific surface area of ​​320 m² / g. S3. Add 0.5% by mass of a compound enzyme preparation to the fermentation substrate to obtain a fermentation substrate mixture. Add 0.3% by mass of polyethylene glycol 600 (99.5% purity) to the above fermentation substrate mixture, then add distilled water, stir evenly, and then enzymatically hydrolyze at a constant temperature. The compound enzyme preparation is prepared by compounding cellulase, xylanase, and protease in a mass ratio of 3.5:2.5:1.5. The mass ratio of the fermentation substrate mixture to distilled water is 1:1.9. S4. After enzymatic hydrolysis, add 1.0% by mass of compound microbial agent and auxiliary additives, with a mass ratio of compound microorganisms to auxiliary additives of 1:12. Enzymatic hydrolysis is performed using a segmented gradient temperature increase: the initial fermentation temperature is 46℃ for 2.2 hours, the middle fermentation temperature is 51℃ for 1.8 hours, and the final fermentation temperature is 54℃ for 0.8 hours. The pH is adjusted to 5.8-6.2 with citric acid. The compound microbial agent consists of Bacillus subtilis, Trichoderma viride, and Saccharomyces cerevisiae, with a mass ratio of 2.5:1.5:1.2. The auxiliary additives consist of sodium alginate, xylooligosaccharides, and chitosan oligosaccharides, with a mass ratio of 1.2:0.5:0.3. S5. Place the fermentation product in an aerobic fermentation device, cover it with a breathable nano-membrane, and adopt segmented fermentation. In the early stage, ferment at 52℃ for 6 days with ventilation twice a day and an oxygen content of 20%; in the later stage, ferment at 60℃ for 4 days with ventilation once a day and an oxygen content of 16%. After fermentation, cool to room temperature, sieve through a 15-mesh sieve to remove impurities, add 0.8% bentonite by mass, dry at 70℃, and stir evenly to obtain the finished organic fertilizer.

[0025] The cellulose crystallinity of the pretreated straw was 22%, and the straw degradation rate was 85%; the organic matter content of the finished organic fertilizer was 65%, the total nutrients of N+P2O5+K2O were 5.8%, and the total humic acid was 18.5%.

[0026] Example 2 S1. Select corn stalks, remove impurities and crush them to 2cm sections. The steam explosion parameters are pressure 0.9MPa, time 40s, and temperature 130℃. After a 5min interval, perform far-infrared radiation with a wavelength of 9μm, power of 600W, and time of 25min. Argon gas is intermittently introduced during the radiation process at a flow rate of 0.5L / min to obtain pretreated stalks. S2. Pretreated straw, peanut meal, humic acid composite raw material and mineral additives are mixed in a mass ratio of 60:15:5:3 to obtain fermentation base material with a carbon-nitrogen ratio of 28:1. The mineral additives are prepared by compounding phosphate rock powder, potassium feldspar and zeolite powder in a mass ratio of 2:1:1. The humic acid composite raw material is prepared by compounding weathered coal, lignite and activated biochar in a mass ratio of 1.5:0.5:0.3. Its particle size is 60 mesh. The biochar is activated at 800℃ and its specific surface area is 300m² / g. S3. Add 0.3% by mass of a compound enzyme preparation to the fermentation substrate to obtain a fermentation substrate mixture. Add 0.2% by mass of food-grade polyethylene glycol 600 (99.5% purity) to the above fermentation substrate mixture, then add distilled water, stir evenly, and then enzymatically hydrolyze at a constant temperature. The compound enzyme preparation is prepared by compounding cellulase, xylanase, and mannanase in a mass ratio of 3:2:1. The mass ratio of the total mass of the compound enzyme preparation and the fermentation substrate to the mass of distilled water is 1:1.8. S4. After enzymatic hydrolysis, add 0.5% by mass of compound microbial agent and auxiliary additives, with a mass ratio of compound microorganisms to auxiliary additives of 1:8. Use segmented gradient temperature enzymatic hydrolysis: early fermentation temperature 45℃ for 2 hours, middle fermentation temperature 50℃ for 1.5 hours, and late fermentation temperature 53℃ for 0.5 hours. Adjust the pH to 5.8-6.2 with citric acid. The compound microbial agent consists of Bacillus licheniformis, Trichoderma thermophilus, and Rhodotorula rubrum, with a mass ratio of 2:1:1. The auxiliary additives consist of sodium alginate, xylooligosaccharides, and chitosan oligosaccharides, with a mass ratio of 0.5:0.3:0.2. S5. Place the fermentation product in an aerobic fermentation device, cover it with a breathable nano-membrane, and adopt segmented fermentation. In the first stage, ferment at 50℃ for 5 days with ventilation twice a day and an oxygen content of 18%; in the second stage, ferment at 55℃ for 3 days with ventilation once a day and an oxygen content of 15%. After fermentation, cool to room temperature, sieve through a 10-mesh sieve to remove impurities, add 0.5% bentonite by mass, dry at 60℃, and stir evenly to obtain the finished organic fertilizer.

[0027] The cellulose crystallinity of the pretreated straw was 25%, and the straw degradation rate was 80%; the organic matter content of the finished organic fertilizer was 60%, the total nutrients of N+P2O5+K2O were 5.0%, and the total humic acid was 16.2%.

[0028] Example 3 S1. Select wheat straw and sorghum straw and mix them at a mass ratio of 2:1. After removing impurities, crush them into 5cm pieces. The steam explosion parameters are pressure 1.1MPa, time 90s, and temperature 160℃. After an interval of 10min, perform far-infrared radiation with a wavelength of 12μm, power of 700W, and time of 35min. During the radiation process, helium gas is intermittently introduced at a flow rate of 1L / min to obtain pretreated straw. S2. Pretreated wheat and sorghum straw, rapeseed meal, humic acid composite raw material and mineral additives are mixed in a mass ratio of 70:25:10:8 to obtain fermentation base material with a carbon-nitrogen ratio of 30:1. The mineral additives are prepared by compounding phosphate rock powder, potassium feldspar and zeolite powder in a mass ratio of 3:2:1. The humic acid composite raw material is prepared by compounding weathered coal, lignite and activated biochar in a mass ratio of 3:2:0.8 with a particle size of 80 mesh. The biochar is activated at 900℃ and has a specific surface area of ​​350 m² / g. S3. Add 0.8% by mass of a compound enzyme preparation to the fermentation substrate to obtain a fermentation substrate mixture. Add 0.5% by mass of food-grade polyethylene glycol 600 (99.8% purity) to the above fermentation substrate mixture, then add distilled water, stir evenly, and then enzymatically hydrolyze at a constant temperature. The compound enzyme preparation is prepared by compounding cellulase, xylanase, and protease in a mass ratio of 4:3:2. The mass ratio of the total mass of the compound enzyme preparation and the fermentation substrate to the mass of distilled water is 1:2. S4. After enzymatic hydrolysis, add 1.5% (w / w) of compound microbial agent and auxiliary additives, with a mass ratio of compound microorganisms to auxiliary additives of 1:15. Enzymatic hydrolysis is performed using a segmented gradient temperature increase: the initial fermentation temperature is 48℃ for 2.5 hours, the middle fermentation temperature is 52℃ for 2 hours, and the final fermentation temperature is 55℃ for 1 hour. The pH is adjusted to 5.8-6.2 with citric acid. The compound microbial agent consists of *Bacillus spp.*: *Trichoderma viride* + *Trichoderma thermophilum*: *Saccharomyces cerevisiae* + *Rhodotorula rubrum*, with a mass ratio of 3:2:1.5. The auxiliary additives are sodium alginate, xylooligosaccharides, and chitosan oligosaccharides, with a mass ratio of 2:0.8:0.5. S5. Place the fermentation product in an aerobic fermentation device, cover it with a breathable nano-membrane, and adopt a staged fermentation method. The initial stage is fermentation at 55℃ for 7 days, with ventilation twice a day and an oxygen content of 22%; the later stage is fermentation at 65℃ for 5 days, with ventilation once a day and an oxygen content of 18%. After fermentation, cool to room temperature, sieve through a 20-mesh sieve to remove impurities, add 1% bentonite by mass, dry at 80℃, and stir evenly to obtain the finished organic fertilizer.

[0029] The cellulose crystallinity of the pretreated straw was 18%, and the straw degradation rate was 88%; the organic matter content of the finished organic fertilizer was 68%, the total nutrients of N+P2O5+K2O were 6.2%, and the total humic acid was 20.3%.

[0030] Comparative Example 1 Compared with Example 1, in the straw pretreatment S1 stage, the straw treatment method is changed to only natural drying treatment, without steam explosion and far-infrared radiation treatment, while the other raw materials and preparation methods are the same as in Example 1.

[0031] The cellulose crystallinity of the pretreated straw was 45%, and the straw degradation rate was 52%. The organic matter content of the finished organic fertilizer was 42%, the total nutrients of N+P2O5+K2O were 3.2%, the total humic acid was 10.8%, and the heavy metal content was 151.1 mg / kg.

[0032] Comparative Example 2 Compared with Example 1, in the enzymatic hydrolysis S3 stage, the compound enzyme agent was changed to a single enzyme agent, as follows: 0.5% by mass of cellulase and 0.3% by mass of food-grade polyethylene glycol 600 were added to the fermentation substrate, and the remaining raw materials and preparation methods were the same as in Example 1.

[0033] The cellulose crystallinity of the pretreated straw was 23%, and the straw degradation rate was 63%. The organic matter content of the finished organic fertilizer was 50%, the total nutrients of N+P2O5+K2O were 3.8%, the total humic acid was 13.5%, and the heavy metal content was 140.8 mg / kg.

[0034] Comparative Example 3 Compared with Example 1, in the S4 stage of microbial fermentation, the segmented enzymatic hydrolysis was changed to constant temperature enzymatic hydrolysis at 50℃, and in the S5 stage, the segmented fermentation was changed to constant temperature fermentation at 55℃. Specifically, after the enzymatic hydrolysis was completed, the same compound microbial agent and auxiliary additives as in Example 1 were added, and the enzymatic hydrolysis was carried out at a constant temperature of 50℃ for 4.8 hours. The fermentation product was placed in an aerobic fermentation device, covered with a breathable nanomembrane, and fermented at a constant temperature of 55℃ for 10 days, with ventilation once a day and an oxygen content of 18%. The remaining raw materials and preparation methods were the same as in Example 1.

[0035] The cellulose crystallinity of the pretreated straw was 22%, and the straw degradation rate was 72%. The organic matter content of the finished organic fertilizer was 58%, the total nutrients of N+P2O5+K2O were 4.5%, the total humic acid was 15.1%, and the heavy metal content was 130.2 mg / kg.

[0036] The organic fertilizers prepared in Examples 1-3 and Comparative Examples 1-3 were tested for key performance indicators. The tests were conducted on the following six performance indicators, as shown in Table 1.

[0037] 1) Straw cellulose crystallinity was determined by X-ray diffraction; 2) Straw degradation rate was determined by microbial degradation; 3) Organic matter content was determined by potassium dichromate solution method; 4) Total humic acid content was determined by potassium dichromate solution method; 5) Total nutrient content (N+P2O5+K2O) was determined by Kjeldahl method for N, by molybdenum-antimony colorimetric method for P2O5, and by flame photometry for K2O; 6) Heavy metal content was determined by atomic absorption spectrophotometry.

[0038] To assess the key performance indicators of straw treatment effect, fermentation efficiency, and organic fertilizer quality, three sets of example organic fertilizers and three sets of comparative organic fertilizers were tested. As shown in Table 1 above, Examples 1-3 all exhibited significant advantages: straw cellulose crystallinity was as low as 18-25%, and the degradation rate reached 80-88%; the finished organic fertilizer had an organic matter content of 60-68%, a total N+P2O5+K2O nutrient content of 5.0-6.2%, and a total humic acid content of 16.2-20.3%; the fermentation cycle was 8-12 days, the high temperature duration was 3-5 days, and the total heavy metal content was controlled between 102.2-116.5 mg / kg, meeting the standards for organic fertilizers.

[0039] Comparative Example 1 replaced steam explosion and far-infrared radiation synergistic pretreatment with natural sun-drying. The results showed that insufficient pretreatment led to lower organic matter content, total nutrients, and total humic acid, and higher total heavy metal content. This indicates that adequate pretreatment not only improves degradation efficiency but also promotes the decomposition and transformation of harmful impurities. Comparative Example 2 replaced compound enzyme preparation with single cellulase. The results showed that single enzyme preparation could not fully decompose the complex components in straw, resulting in insufficient fertilizer efficiency of the finished product. Comparative Example 3 eliminated segmented temperature control and adopted constant temperature enzymatic hydrolysis and constant temperature fermentation. The results showed that the constant temperature process could not meet the temperature requirements for the synergistic effect of enzymes and bacteria, resulting in insufficient stability of the fermentation system, insufficient degree of decomposition, and thus affecting the quality of the finished organic fertilizer.

[0040] This invention employs a synergistic pretreatment process combining steam explosion and far-infrared radiation, a multi-enzyme synergy process using compound enzyme preparations, and segmented temperature-controlled fermentation, all of which play a crucial role in improving straw degradation efficiency and organic fertilizer quality. The core indicators of the finished organic fertilizer far exceed existing technological levels, exhibiting low heavy metal content, stable fertilizer efficacy, and improved soil physicochemical properties, thus achieving efficient and environmentally friendly resource utilization of straw. Natural drying, single enzyme preparations, and constant-temperature fermentation all suffer from insufficient straw degradation, poor fertilizer efficacy, and inadequate stability. This invention, through multi-stage synergistic innovation, effectively solves these pain points, providing an efficient and feasible technical solution for the resource utilization of straw.

[0041] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be modified within the scope of the concept described in this patent through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw, characterized in that, Includes the following steps: S1. Select straw as raw material, remove impurities such as stones and weeds, and then crush it with a crusher to obtain pre-treated straw. S2. Mix the pretreated straw, nitrogen source material, humic acid composite material and mineral additives evenly in a mass ratio of (60~70):(15~25):(5~10):(3~8) to obtain the fermentation base material; S3. Add the compound enzyme preparation to the fermentation substrate in sequence to obtain the fermentation substrate mixture, then add distilled water, stir evenly and then enzymatically hydrolyze; the mass ratio of the fermentation substrate mixture to distilled water is 1:(1.8~2); S4. After enzymatic hydrolysis, add compound microbial agent and auxiliary additives in sequence to obtain fermentation product; the mass fraction of compound microbial agent is 0.5~1.5%, and the mass ratio of compound microorganism to auxiliary additive is 1:(8~15). S5. Place the fermentation product in an aerobic fermentation device. After fermentation, cool it to room temperature, sieve and remove impurities, add 0.5-1% bentonite by mass, and dry it at a low temperature of 60-80℃ to obtain the finished organic fertilizer.

2. The method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw according to claim 1, wherein the straw in step S1 is at least one of corn straw, wheat straw, rice straw and sorghum straw.

3. The method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw according to claim 1, wherein the crushed straw needs to be treated by steam explosion and far-infrared radiation in a coordinated manner, wherein the process parameters of the steam explosion are pressure 0.9~1.1MPa, time 40~90s, and temperature 130~160℃; and the wavelength of the far-infrared radiation is 9~12μm, power 600~700W, and time 25~35min.

4. In the method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw according to claim 3, an inert gas is intermittently introduced during the far-infrared radiation process. The inert gas is any one of nitrogen, argon, or helium, and the flow rate is 0.5~1L / min.

5. The method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw according to claim 1, wherein the humic acid composite raw material in step S2 is prepared by compounding weathered coal, lignite and biochar in a mass ratio of (1.5~3):(0.5~2):(0.3~0.8); the nitrogen source auxiliary material is any one of soybean meal, peanut meal, rapeseed meal and soybean protein residue; the mineral additive is prepared by compounding phosphate rock powder, potassium feldspar and zeolite powder in a mass ratio of (2~3):(1~2):

1.

6. The method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw according to claim 5, wherein the biochar is activated at 800-900℃, and the activated biochar has a specific surface area ≥300m². 2 / g.

7. The method for preparing organic fertilizer by enzymatic fermentation of crop straw according to claim 1, wherein the mass fraction of the compound enzyme in step S3 is 0.3-0.8%; the compound enzyme is prepared by compounding cellulase, xylanase, and protease / mannanase in a mass ratio of 3-4:2-3:1-2; and 0.2-0.5% of polyethylene glycol 600 is added to the compound enzyme.

8. The method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw according to claim 1, wherein the compound microbial agent in step S4 is composed of Bacillus, Trichoderma, and yeast, and the mass ratio of the three bacteria is 2~3:1~2:1~1.5; the auxiliary additive is a compound of sodium alginate, xylooligosaccharide, and chitosan oligosaccharide, and the mass ratio is 0.5~2:0.3~0.8:0.2~0.5; the Bacillus is at least one of Bacillus subtilis, Bacillus licheniformis, and Bacillus spathulatus; the Trichoderma is at least one of Trichoderma viride and Trichoderma thermophilum; and the yeast is at least one of Saccharomyces cerevisiae and Rhodotorula rubra.

9. The method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw according to any one of claims 1 to 9, wherein a gradient temperature is adopted in the enzymatic hydrolysis stage, with the initial fermentation temperature at 45-48℃ and the time at 2-2.5h; the middle fermentation temperature at 50-52℃ and the time at 1.5-2h; and the later fermentation temperature at 53-55℃ and the time at 0.5-1h; and the pH is adjusted to 5.8-6.2 with citric acid.

10. The method for preparing organic fertilizer by enzymatic hydrolysis and fermentation of crop straw according to claim 10, wherein the fermentation stage adopts segmented fermentation, the initial fermentation temperature is 50~55℃ and the time is 5~7 days, the soil is turned over twice a day, and the oxygen content is 18~22%; the later fermentation temperature is 55~65℃ and the time is 3~5 days, the soil is turned over once a day, and the oxygen content is 15~18%.

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