Agricultural waste bio-organic fertilizer and preparation method thereof

Abstract

The present application belongs to the technical field of waste conversion fertilizer, and provides an agricultural waste bio-organic fertilizer and a preparation method thereof.The preparation method comprises the following steps: S1, mixing 100-105 parts of agricultural waste, 1-2 parts of humic acid, 5-7 parts of ore powder and 0.4-0.6 parts of compound strains according to mass fraction to obtain a first mixture; S2, adding 50-55 parts of water into the first mixture, and placing the mixture in a fermentation tank to ferment, so as to obtain a fermentation product; S3, drying and granulating the fermentation product to obtain organic fertilizer particles; and S4, adding the organic fertilizer particles into a coating machine, spraying coating liquid onto the surface of the organic fertilizer particles through a spray gun, and then introducing hot air to evaporate water, and then cooling and sieving, so as to obtain the agricultural waste bio-organic fertilizer.The coating liquid comprises water and a coating material, and the coating material comprises 80-85 parts of modified hydroxypropyl methyl cellulose, 3-5 parts of polyvinyl alcohol, 5-8 parts of magnesium-aluminum hydrotalcite powder and 4-5 parts of citric acid according to mass fraction.The present application can reduce the release speed of fertilizer components, and effectively improve the slow-release effect of the prepared agricultural waste bio-organic fertilizer.

Description

Technical Field

[0001] This invention belongs to the field of waste-to-fertilizer technology, specifically relating to an agricultural waste bio-organic fertilizer and its preparation method. Background Technology

[0002] In existing technologies, the process of making organic fertilizer from straw involves crushing the straw and mixing it with other materials to prepare a powder. This powder is then granulated and coated to form granules, which are then coated onto the surface of the granules to create a slow-release fertilizer. Current coating methods use hydroxypropyl cellulose and citric acid as a pore-forming agent. In humid environments, citric acid and hydroxypropyl cellulose absorb water, forming channels for releasing the fertilizer's active ingredients. However, citric acid itself absorbs and releases water rapidly, leading to an excessively fast release rate of the fertilizer components / nutrients, resulting in poor slow-release effects. Summary of the Invention

[0003] To address the problems existing in the background technology, the present invention provides an agricultural waste bio-organic fertilizer and its preparation method, which can reduce the release rate of fertilizer components, prolong the stable release cycle of nutrients, and effectively improve the slow-release effect of the prepared agricultural waste bio-organic fertilizer.

[0004] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing agricultural waste bio-organic fertilizer, comprising the following steps:

[0005] S1. By weight, mix 100-105 parts agricultural waste, 1-2 parts humic acid, 5-7 parts mineral powder and 0.4-0.6 parts compound microbial inoculum to obtain the first mixture.

[0006] S2. Add 50-55 parts of water to the first mixture obtained in S1 to obtain the second mixture. Place the second mixture in a fermentation tank for sealed fermentation to obtain the fermented product.

[0007] S3. The fermented product obtained in S2 is dried and then granulated using a granulator to obtain organic fertilizer granules.

[0008] S4. Add the organic fertilizer granules into the coating machine, spray the coating liquid onto the surface of the organic fertilizer granules through the spray gun, pass in hot air to evaporate the moisture, cool, and sieve to obtain the agricultural waste bio-organic fertilizer.

[0009] The coating solution comprises water and coating material, which, by weight, comprises 80-85 parts modified hydroxypropyl methylcellulose, 3-5 parts polyvinyl alcohol, 5-8 parts magnesium aluminum hydrotalcite powder, and 4-5 parts citric acid.

[0010] Furthermore, the method for preparing the modified hydroxypropyl methylcellulose is as follows:

[0011] A1. Hydroxypropyl methylcellulose was dissolved in 1,4-dioxane to obtain the first solution. The ratio of hydroxypropyl methylcellulose to 1,4-dioxane was 1g:45-50mL.

[0012] A2. Add phthalic anhydride, triethylamine catalyst and toluene to the first solution obtained in A1. The mass ratio of phthalic anhydride to hydroxypropyl methylcellulose is 0.85:1. React at a temperature of 85±2℃ for 4-5 hours. Dehydrate the solution by using toluene-water azeotrope to obtain the reaction solution.

[0013] A3. Cool the reaction solution obtained in A2 to 30°C, and add deionized water dropwise at a rate of 40 mL / min while stirring. Flocculent precipitate will form. The mass ratio of deionized water to hydroxypropyl methylcellulose is (18-22):1.

[0014] A4. Filter the precipitate obtained from A3 and wash it with deionized water until the pH of the filtrate is 6.5-7.0. The solid obtained is then vacuum dried at 55℃ and -0.08MPa for 5-6 hours to obtain modified hydroxypropyl methylcellulose.

[0015] Furthermore, in A2, the mass ratio of hydroxypropyl methylcellulose to triethylamine is 1:0.08, and the volume of toluene is 40% of the volume of 1,4-dioxane.

[0016] Furthermore, in S1, agricultural waste is crop straw; the compound bacteria include Bacillus subtilis and Bacillus amyloliquefaciens, with a viable count ≥500 million / g.

[0017] Furthermore, in S2, the fermentation temperature is 50-60℃, the fermentation cycle is 15-20 days, and the pile is turned over once every 72 hours.

[0018] Furthermore, in S4, the atomization pressure is 0.2-0.3 MPa, the hot air temperature is ≤60℃, and the coating material accounts for 3.2%-4.0% of the mass of the organic fertilizer granules.

[0019] Furthermore, in the coating solution, the mass ratio of coating material to water is (3-4):20.

[0020] Secondly, the present invention provides an agricultural waste bio-organic fertilizer, which is prepared by the above-described preparation method.

[0021] This application has the following beneficial effects:

[0022] The coating material of this invention includes modified hydroxypropyl methylcellulose, polyvinyl alcohol, magnesium aluminum hydrotalcite powder, and citric acid. On one hand, the layered structure of the magnesium aluminum hydrotalcite powder preferentially adsorbs citric acid molecules, reducing the free acid concentration and inhibiting catalytic activity; furthermore, the magnesium aluminum hydrotalcite powder itself releases OH- upon contact with water. - It can neutralize the H produced by citric acid.+ Maintaining a local pH of 6.0-7.0 further reduces the rate of ester bond hydrolysis, thereby significantly prolonging the gel network disintegration time.

[0023] On the other hand, the interlayer channels of magnesium aluminum hydrotalcite powder can also adsorb environmental moisture, reduce the water absorption and swelling rate of the three-dimensional gel network formed by the modified hydroxypropyl methylcellulose generated by esterification after water absorption, that is, enhance the compactness of the three-dimensional gel network, thereby slowing down the nutrient diffusion rate and synergistically improving the slow-release effect of the agricultural waste bio-organic fertilizer. Attached Figure Description

[0024] Figure 1 A comparative graph showing the cumulative nutrient release rate curves of agricultural waste bio-organic fertilizers prepared in Examples 1-4 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0025] The present application will be further described in detail below with reference to the embodiments.

[0026] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0027] Example 1: (a) Preparation of modified hydroxypropyl methylcellulose, the preparation method is as follows:

[0028] A1. Hydroxypropyl methylcellulose (HPMC) was dissolved in 1,4-dioxane. HPMC powder was added gradually while mechanically stirring at 800 rpm and at 40°C until completely dispersed. The solution was a transparent, particle-free colloid that showed no stratification after standing for 30 minutes, yielding the first solution. The ratio of hydroxypropyl methylcellulose to 1,4-dioxane was 1 g: 46 mL.

[0029] A2. Add phthalic anhydride (added in 3 batches with 15 min intervals to prevent local overheating and degradation), triethylamine catalyst (added all at once), and toluene to the first solution obtained in A1. The mass ratio of phthalic anhydride to hydroxypropyl methylcellulose is 0.85:1, the mass ratio of hydroxypropyl methylcellulose to triethylamine is 1:0.08, and the volume of toluene is 40% of the volume of 1,4-dioxane. React at 85°C for 4.5 h under nitrogen protection (flow rate 0.5 L / min). Dehydrate the mixture by passing it through a toluene-water azeotrope (reflux rate of 3-4 drops / second in the condenser) to obtain the reaction solution.

[0030] A3. Cool the reaction solution obtained in A2 to 30℃ at a cooling rate of 4℃ / min to avoid excessive temperature difference causing impurities to be trapped in the product. Add deionized water dropwise at a rate of 40mL / min under mechanical stirring at 500rpm (slowly add along the reactor wall). The mass ratio of deionized water to hydroxypropyl methylcellulose is 20:1. Excess water ensures complete precipitation. The flocculent precipitate is a milky white gel.

[0031] A4. Filter the flocculent precipitate obtained from A3 and wash it with deionized water until the pH of the filtrate is about 6.8. The solid obtained is then vacuum dried at 55℃ and -0.08MPa for 5.5h to obtain modified hydroxypropyl methylcellulose.

[0032] (II) Preparation of the coating solution: The preparation method is as follows: Mix the coating material and water at a mass ratio of 3.5:20. Specifically, first add the total amount of water (deionized water, 25±2℃) to the stirring container, turn on the high-speed shear disperser (speed 800 rpm), and slowly and evenly add the coating material. First, perform initial dispersion: 1500 rpm, 10 min; then perform high-speed homogenization: 3000 rpm, 20 min, to form a uniform milky white liquid; finally, defoaming and maturation: 50 rpm, 30 min, until no visible bubbles are visible and the viscosity is stable. The coating solution should be used within 24 hours after preparation to avoid microbial growth or viscosity increase.

[0033] The coating material is prepared as follows: 83 parts by weight of modified hydroxypropyl methylcellulose, 4 parts by weight of polyvinyl alcohol, 6 parts by weight of magnesium aluminum hydrotalcite powder, and 4.5 parts by weight of citric acid are mixed evenly. Specifically: ① Initial mixing of the base: One-third (approximately 27.7 parts) of the total modified hydroxypropyl methylcellulose (83 parts) is added to a three-dimensional motion mixer as the base. ② Premixing of additives: 4 parts by weight of polyvinyl alcohol and 3 parts by weight of magnesium aluminum hydrotalcite powder are premixed evenly and then added to the mixer, and mixed for 10 minutes. ③ Gradually adding the remaining modified hydroxypropyl methylcellulose and magnesium aluminum hydrotalcite powder: The remaining modified hydroxypropyl methylcellulose and magnesium aluminum hydrotalcite powder are added in three equal portions, with a 5-minute interval between each addition, while maintaining a rotation speed of 25 rpm throughout. ④ Finally, 4.5 parts by weight of citric acid are added, and the mixture is stirred for another 10 minutes to obtain the final product.

[0034] (III) A method for preparing agricultural waste bio-organic fertilizer, comprising the following steps:

[0035] S1. By weight, 102 parts of agricultural waste (corn stalks crushed to a particle size of 1-5 cm, controlled by a sieve, and dried to a moisture content of 12%), 1.5 parts of humic acid, 6 parts of mineral powder (added in 3 batches during mixing to prevent dust), and 0.5 parts of compound microbial inoculum (11 parts of activated compound microbial solution) are added to a double-helix mixer at 25 rpm for 20 minutes. After mixing evenly, the first mixture is obtained. The compound microorganisms include Bacillus subtilis and Bacillus amyloliquefaciens, with a mass ratio of 2:1. The viable count of Bacillus subtilis is 5.3 × 10⁻⁶. 8 / g, the viable count of Bacillus amyloliquefaciens was 6.1×10⁶. 8 / g. Before use, mix 0.5 parts of compound bacteria with 0.5 parts of brown sugar and 10 parts of warm water at 35℃, let stand for 30 minutes to activate, and then use the activated compound bacteria solution.

[0036] S2. Add 54 parts of water to the first mixture obtained in S1 to obtain the second mixture. Place the second mixture in a fermentation tank for sealed fermentation. The pile has a trapezoidal cross section. The fermentation temperature is 50-60℃. Turn the pile once every 72 hours. The fermentation cycle is 18 days. When the material turns dark brown, has no ammonia odor, and white mycelium covers the surface, the fermented product is obtained.

[0037] S3. Use a belt dryer to dry the fermented material obtained in S2. The inlet air temperature is 75±5℃ and the material layer thickness is about 4cm. After drying, the moisture content is about 10%. Then, use a rotary drum granulator to granulate the material at a speed of 20rpm and an inclination angle of 45° to obtain organic fertilizer granules with a diameter of 3-5mm.

[0038] S4. Add organic fertilizer granules to the coating machine, spray coating liquid onto the surface of organic fertilizer granules through a spray gun. The coating material accounts for 3.5% of the mass of organic fertilizer granules. The atomization pressure is 0.25MPa. Hot air is introduced to evaporate moisture. The hot air temperature is 55℃ and the wind speed is 1.8m / s. The fluidized bed is cooled to 30℃. After sieving, agricultural waste bio-organic fertilizer is obtained.

[0039] Example 2: The difference between this example and Example 1 is that the coating solution is prepared as follows: the coating material and water are mixed at a mass ratio of 3:20. The coating material is prepared as follows: 80 parts by mass of modified hydroxypropyl methylcellulose, 3 parts by mass of polyvinyl alcohol, 5 parts by mass of magnesium aluminum hydrotalcite powder, and 4 parts by mass of citric acid are mixed.

[0040] Example 3: The difference between this example and Example 1 is that the coating solution is prepared as follows: the coating material and water are mixed at a mass ratio of 4:20. The coating material is prepared as follows: 85 parts by mass of modified hydroxypropyl methylcellulose, 5 parts by mass of polyvinyl alcohol, 8 parts by mass of magnesium aluminum hydrotalcite powder, and 5 parts by mass of citric acid are mixed.

[0041] Example 4: The difference between this example and Example 1 is that the coating solution is prepared as follows: the coating material and water are mixed at a mass ratio of 3.8:20. The coating material is prepared as follows: 81 parts by mass of modified hydroxypropyl methylcellulose, 4.2 parts by mass of polyvinyl alcohol, 6 parts by mass of magnesium aluminum hydrotalcite powder, and 5 parts by mass of citric acid are mixed.

[0042] Comparative Example 1: The difference between this comparative example and Example 1 is that in the preparation of the coating material, the modified hydroxypropyl methylcellulose is replaced with hydroxypropyl methylcellulose; and magnesium aluminum hydrotalcite powder is not added.

[0043] Specifically, the coating material is prepared as follows: 83 parts by weight of hydroxypropyl methylcellulose, 4 parts by weight of polyvinyl alcohol and 4.5 parts by weight are mixed evenly to obtain the coating material.

[0044] Comparative Example 2: The difference between this comparative example and Example 1 is that magnesium aluminum hydrotalcite powder is not added in the preparation of the coating material.

[0045] Specifically, the coating material is prepared as follows: 83 parts of modified hydroxypropyl methylcellulose, 4 parts of polyvinyl alcohol and 4.5 parts of citric acid are mixed by weight to obtain the coating material.

[0046] Comparative Example 3: The difference between this comparative example and Example 1 is that in the preparation of the coating material, the modified hydroxypropyl methylcellulose is replaced with hydroxypropyl methylcellulose.

[0047] Specifically, the coating material is prepared as follows: 83 parts of hydroxypropyl methylcellulose, 4 parts of polyvinyl alcohol, 6 parts of magnesium aluminum hydrotalcite powder and 4.5 parts of citric acid are mixed by weight to obtain the coating material.

[0048] Experimental Example: The cumulative nutrient release rate of agricultural waste bio-organic fertilizers prepared in Examples 1-4 and Comparative Examples 1-3 was determined according to GB / T 23348-2009. The total nitrogen release rate was the characterization factor. Experimental Method: 20g of organic fertilizer (accurate to 0.01g) was weighed and placed in a small bag made of 100-mesh nylon mesh. After sealing, the bag was placed in a 500mL glass bottle, 400mL of distilled water was added, the bottle was sealed, and the bottle was placed in a 25℃ biochemical constant temperature incubator. Sampling was conducted at 1d, 3d, 7d, 14d, 28d, and 56d. Sampling was stopped when the cumulative nutrient release rate reached 80%. During sampling, the bottle was inverted three times to ensure a consistent liquid concentration. Experimental Results: See Table 1.

[0049] Table 1. Experimental Data

[0050]

[0051] Results Analysis: Combining the data in Table 1 and... Figure 1 Analysis of Examples 1-4 and Comparative Examples 1-3 shows that the agricultural waste bio-organic fertilizer prepared by the present invention (Examples 1-4) can stably release nutrients, and the overall release rate is reduced, the stable nutrient release period is extended, and the slow-release effect is more excellent.

[0052] A detailed analysis of Comparative Examples 1 and 2 reveals that, compared to Comparative Example 1 (which did not contain magnesium aluminum hydrotalcite powder), Comparative Example 2, by converting the raw material hydroxypropyl methylcellulose (the coating material) into the modified hydroxypropyl methylcellulose of this invention, resulted in a significantly faster release of nutrients from the agricultural waste bio-organic fertilizer. This indicates that converting hydroxypropyl methylcellulose alone into the modified hydroxypropyl methylcellulose of this invention accelerates the release rate of nutrients from the final agricultural waste bio-organic fertilizer, leading to a shorter stable nutrient release cycle.

[0053] This is mainly because the modified hydroxypropyl methylcellulose generated by esterification forms a three-dimensional gel network after absorbing water, which can slow down nutrient diffusion and reduce the fertilizer effect / nutrient release rate. However, citric acid in the coating solution will preferentially dissolve in a humid environment, and its acidity (pH≈2.1) can catalyze the hydrolysis of ester bonds, which will cause the gel network to disintegrate prematurely. That is, the catalytic hydrolysis rate of citric acid is greater than the barrier effect of the gel network, which leads to the fertilizer effect / nutrient release rate increasing instead of decreasing, and the stable nutrient release cycle is shortened.

[0054] Specific analysis of Comparative Examples 1 and 3 shows that, compared to Comparative Example 1, the addition of magnesium aluminum hydrotalcite powder to the raw materials of the coating material in Comparative Example 3 significantly slowed down the nutrient release rate of the resulting agricultural waste bio-organic fertilizer. This indicates that adding magnesium aluminum hydrotalcite powder to the raw material components of the coating material can slow down the nutrient release rate of the final agricultural waste bio-organic fertilizer. Further analysis of Example 1 shows that the addition of magnesium aluminum hydrotalcite powder to the raw material components of the coating material, and the conversion of the raw material hydroxypropyl methylcellulose into the modified hydroxypropyl methylcellulose of this invention, can produce a synergistic effect, synergistically reducing the nutrient release rate of the final agricultural waste bio-organic fertilizer, thereby extending the stable nutrient release period.

[0055] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0056] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing agricultural waste bio-organic fertilizer, characterized in that, Includes the following steps: S1. By weight, mix 100-105 parts agricultural waste, 1-2 parts humic acid, 5-7 parts mineral powder and 0.4-0.6 parts compound microbial inoculum to obtain the first mixture; the agricultural waste is crop straw. S2. Add 50-55 parts of water to the first mixture obtained in S1 to obtain the second mixture. Place the second mixture in a fermentation tank for sealed fermentation to obtain the fermented product. S3. The fermented product obtained in S2 is dried and then granulated using a granulator to obtain organic fertilizer granules. S4. Add the organic fertilizer granules into the coating machine, spray the coating liquid onto the surface of the organic fertilizer granules through the spray gun, pass in hot air to evaporate the moisture, cool, and sieve to obtain the agricultural waste bio-organic fertilizer. The coating solution includes water and coating material, which, by weight, includes 80-85 parts of modified hydroxypropyl methylcellulose, 3-5 parts of polyvinyl alcohol, 5-8 parts of magnesium aluminum hydrotalcite powder, and 4-5 parts of citric acid. The modified hydroxypropyl methylcellulose is prepared as follows: A1. Hydroxypropyl methylcellulose was dissolved in 1,4-dioxane to obtain the first solution. The ratio of hydroxypropyl methylcellulose to 1,4-dioxane was 1g:45-50mL. A2. Add phthalic anhydride, triethylamine catalyst and toluene to the first solution obtained in A1. The mass ratio of phthalic anhydride to hydroxypropyl methylcellulose is 0.85:

1. React at a temperature of 85±2℃ for 4-5 hours. Dehydrate the solution by using toluene-water azeotrope to obtain the reaction solution. A3. Cool the reaction solution obtained in A2 to 30°C, and add deionized water dropwise at a rate of 40 mL / min while stirring. Flocculent precipitate will form. The mass ratio of deionized water to hydroxypropyl methylcellulose is (18-22):

1. A4. Filter the precipitate obtained in A3 and wash it with deionized water until the pH of the filtrate is 6.5-7.

0. The solid obtained is then vacuum dried at 55℃ and -0.08MPa for 5-6 hours to obtain modified hydroxypropyl methylcellulose.

2. The method for preparing agricultural waste bio-organic fertilizer according to claim 1, characterized in that, In A2, the mass ratio of hydroxypropyl methylcellulose to triethylamine is 1:0.08, and the volume of toluene is 40% of the volume of 1,4-dioxane.

3. The method for preparing agricultural waste bio-organic fertilizer according to claim 1, characterized in that, In S1, the compound bacteria include Bacillus subtilis and Bacillus amyloliquefaciens, with a viable count ≥500 million / g.

4. The method for preparing agricultural waste bio-organic fertilizer according to claim 1, characterized in that, In S2, the fermentation temperature is 50-60℃, the fermentation cycle is 15-20 days, and the pile is turned over once every 72 hours.

5. The method for preparing agricultural waste bio-organic fertilizer according to claim 1, characterized in that, In S4, the atomization pressure is 0.2-0.3MPa, and the hot air temperature is ≤60℃; the coating material accounts for 3.2%-4.0% of the mass of the organic fertilizer granules.

6. The method for preparing agricultural waste bio-organic fertilizer according to claim 1, characterized in that, In the coating solution, the mass ratio of coating material to water is (3-4):

20.

7. An agricultural waste bio-organic fertilizer, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

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