Agricultural waste bio-organic fertilizer and preparation method thereof

Abstract

The invention belongs to the technical field of waste converted fertilizers. The invention provides an agricultural waste bio-organic fertilizer and a preparation method thereof.The preparation method comprises the steps that S1, 100-105 parts by mass of agricultural waste, 1-2 parts by mass of humic acid, 5-7 parts by mass of mineral powder and 0.4-0.6 part by mass of composite strains are mixed, and a first mixture is obtained; s2, adding 50-55 parts of water into the first mixture, and fermenting in a fermentation tank to obtain a fermented product; s3, drying and granulating the fermented product to obtain organic fertilizer particles; and S4, adding the organic fertilizer particles into a coating machine, spraying the coating liquid to the surfaces of the organic fertilizer particles through a spray gun, introducing hot air to evaporate moisture, cooling, and sieving to obtain the organic fertilizer. The coating liquid comprises water and a coating material, and the coating material comprises the following components in parts by mass: 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. The release speed of fertilizer efficiency components can be reduced, and the slow release effect of the prepared agricultural waste bio-organic fertilizer is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of waste conversion fertilizer, and particularly relates to an agricultural waste bio-organic fertilizer and a preparation method thereof. Background Art

[0003] In the prior art, straw is used to make organic fertilizer by crushing the straw and mixing it with other substances to form a powder. The powder is then granulated and coated to form a granular material. The powder is then adhered to the surface of the granular material to form a slow-release fertilizer. Existing coatings use hydroxypropyl cellulose and citric acid as a pore-forming agent. In a humid environment, the citric acid and hydroxypropyl cellulose absorb water to form channels for releasing the fertilizer components. However, citric acid itself absorbs water and precipitates quickly, which can cause the fertilizer components / nutrients to be released too quickly, resulting in a poor slow-release effect. Summary of the Invention

[0004] In order to solve the problems existing in the background technology, the present invention provides an agricultural waste bio-organic fertilizer and a preparation method thereof, which can reduce the release rate of fertilizer components, prolong the stable nutrient release period, and effectively improve the slow-release effect of the obtained agricultural waste bio-organic fertilizer.

[0005] In order 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:

[0006] S1. Mixing, by mass, 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 the composite bacterial strain to obtain a first mixture;

[0007] S2. Add 50-55 parts of water to the first mixture obtained in S1 to obtain a second mixture, and place the second mixture in a fermentation tank for sealed fermentation to obtain a fermentation product;

[0008] S3, drying the fermented product obtained in S2, and then granulating it using a granulator to obtain organic fertilizer granules;

[0009] S4, adding the organic fertilizer particles into a coating machine, spraying the coating liquid onto the surface of the organic fertilizer particles through a spray gun, passing hot air to evaporate the water, cooling, and sieving to obtain the agricultural waste bio-organic fertilizer;

[0010] The coating liquid comprises water and a coating material, wherein the coating material comprises, by mass, 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.

[0011] Furthermore, the preparation method of the modified hydroxypropyl methylcellulose is as follows:

[0012] A1. Dissolve hydroxypropyl methylcellulose in 1,4-dioxane to obtain a first solution, wherein the ratio of hydroxypropyl methylcellulose to 1,4-dioxane is 1 g:45-50 mL;

[0013] A2, adding phthalic anhydride, triethylamine catalyst and toluene to the first solution obtained in A1, with a mass ratio of phthalic anhydride to hydroxypropyl methylcellulose of 0.85:1, and reacting at a temperature of 85±2°C for 4-5 hours, and dehydrating through a toluene-water azeotrope to obtain a reaction solution;

[0014] A3. Cool the reaction solution obtained in A2 to 30°C, add deionized water dropwise at a rate of 40 mL / min with stirring to precipitate a flocculent precipitate. The mass ratio of deionized water to hydroxypropyl methylcellulose is (18-22):1;

[0015] A4. Filter the precipitate obtained in A3 and rinse with deionized water until the filtrate has a pH of 6.5-7.0. The solid is vacuum-dried at 55° C. and −0.08 MPa for 5-6 h to obtain modified hydroxypropyl methylcellulose.

[0016] 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.

[0017] Furthermore, in S1, the agricultural waste is crop straw; the composite bacteria include Bacillus subtilis and Bacillus amyloliquefaciens, and the number of viable bacteria is ≥ 500 million / g.

[0018] Furthermore, in S2, the fermentation temperature is 50-60°C, the fermentation period is 15-20 days, and the compost is turned once every 72 hours.

[0019] Furthermore, in S4, the atomization pressure is 0.2-0.3 MPa, the hot air temperature is ≤60°C, and the coating material accounts for 3.2%-4.0% of the mass of the organic fertilizer particles.

[0020] Furthermore, in the coating solution, the mass ratio of the coating material to water is (3-4):20.

[0021] In a second aspect, the present invention provides an agricultural waste bio-organic fertilizer, which is prepared using the above-mentioned preparation method.

[0022] This application has the following beneficial effects:

[0023] The coating material of the present invention comprises modified hydroxypropyl methylcellulose, polyvinyl alcohol, magnesium aluminum hydrotalcite and citric acid. On the one hand, the layered structure of magnesium aluminum hydrotalcite can preferentially adsorb citric acid molecules, reduce the free acid concentration, and inhibit catalytic activity; and on the other hand, magnesium aluminum hydrotalcite itself releases OH groups when it comes into contact with water. -, which can neutralize H produced by citric acid + , maintaining the local pH ≈ 6.0-7.0, further reducing the ester bond hydrolysis rate; thereby significantly prolonging the gel network disintegration time.

[0024] On the other hand, the interlayer channels of magnesium-aluminum hydrotalcite can also absorb environmental moisture, reduce the water absorption and expansion rate of the modified hydroxypropyl methylcellulose generated by esterification to form a three-dimensional gel network after absorbing water, that is, enhance the density of the three-dimensional gel network, and then delay the nutrient diffusion rate, synergistically improving the slow-release effect of the agricultural waste bio-organic fertilizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 , a comparison chart of the cumulative nutrient release rate curves of the agricultural waste bio-organic fertilizers prepared in Examples 1 to 4 and Comparative Examples 1 to 3 in the test examples of the present invention. DETAILED DESCRIPTION

[0026] The present application is further described in detail below with reference to the embodiments.

[0027] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0028] Example 1: (1) Preparation of modified hydroxypropyl methylcellulose, the preparation method is as follows:

[0029] A1. Dissolve hydroxypropyl methylcellulose (HPMC) in 1,4-dioxane and gradually add HPMC powder. Stir mechanically at 800 rpm and 40°C until completely dispersed. The solution becomes a transparent, particle-free colloid. After standing for 30 minutes, no stratification occurs, thereby obtaining the first solution. The ratio of hydroxypropyl methylcellulose to 1,4-dioxane is 1 g:46 mL.

[0030] A2. To the first solution obtained in A1, phthalic anhydride (added in three batches with an interval of 15 minutes to prevent degradation caused by local overheating), triethylamine catalyst (added all at once) and toluene were added, the mass ratio of phthalic anhydride to hydroxypropyl methylcellulose was 0.85:1, the mass ratio of hydroxypropyl methylcellulose to triethylamine was 1:0.08, the volume of toluene was 40% of the volume of 1,4-dioxane, and the mixture was reacted at 85° C. under nitrogen protection (flow rate 0.5 L / min) for 4.5 hours, and dehydrated by toluene-water azeotrope (condenser reflux rate of 3-4 drops / second) to obtain a reaction solution.

[0031] A3. Cool the reaction solution obtained in A2 to 30°C at a cooling rate of 4°C / min to avoid product inclusion of impurities due to large temperature differences. Add deionized water dropwise at a rate of 40 mL / min (slowly dripping along the reactor wall) with mechanical stirring at 500 rpm. The mass ratio of deionized water to hydroxypropyl methylcellulose is 20:1. Excess water ensures complete precipitation. The flocculent precipitate becomes a milky white gel.

[0032] A4. Filter the flocculent precipitate obtained in A3 and rinse with deionized water until the filtrate has a pH of about 6.8. The obtained solid is vacuum dried at 55°C and -0.08 MPa for 5.5 h to obtain modified hydroxypropyl methylcellulose.

[0033] (2) Prepare the coating solution. The preparation method is as follows: mix the coating material and water in a mass ratio of 3.5:20. Specifically, add the total amount of water (deionized water, 25±2°C) to the stirring container, turn on the high-speed shear disperser (speed 800rpm), and slowly and evenly add the coating material. First, perform initial dispersion: 1500rpm, 10min; then perform high-speed homogenization: 3000rpm, 20min to form a uniform milky white liquid; finally, defoaming and aging: 50rpm, 30min to achieve no visible bubbles and stable viscosity. The coating solution should be used up within 24h after preparation to avoid microbial growth or viscosity increase.

[0034] Among them, the preparation method of the coating material is as follows: by mass, 83 parts of modified hydroxypropyl methylcellulose, 4 parts of polyvinyl alcohol, 6 parts of magnesium aluminum hydrotalcite and 4.5 parts of citric acid are mixed to obtain. Specifically, ① initial mixing of the base: 1 / 3 (about 27.7 parts) of the total amount of modified hydroxypropyl methylcellulose (83 parts) is put into a three-dimensional motion mixer as a base. ② Premixing additives: After premixing 4 parts of polyvinyl alcohol and 3 parts of magnesium aluminum hydrotalcite, add them to the mixer and mix and stir for 10 minutes. ③ Add the remaining modified hydroxypropyl methylcellulose and magnesium aluminum hydrotalcite in batches: The remaining modified hydroxypropyl methylcellulose and magnesium aluminum hydrotalcite are added together in 3 equal parts, each time with an interval of 5 minutes, and the speed is always maintained at 25rpm. ④ Finally, add 4.5 parts of citric acid and continue stirring for 10 minutes to obtain.

[0035] (3) A method for preparing agricultural waste bio-organic fertilizer, comprising the following steps:

[0036] S1. Add 102 parts by mass of agricultural waste (corn straw crushed to a particle size of 1-5 cm, sieved, and air-dried to a moisture content of 12%), 1.5 parts of humic acid, 6 parts of mineral powder (added three times during mixing to prevent dust), and 0.5 parts of composite bacteria (11 parts of activated composite bacteria solution) into a double-screw mixer at a speed of 25 rpm for 20 minutes. After uniform mixing, a first mixture is obtained. The composite bacteria include Bacillus subtilis and Bacillus amyloliquefaciens, with a mass ratio of Bacillus subtilis to Bacillus amyloliquefaciens of 2:1, and the viable cell count of Bacillus subtilis is 5.3×10 8 / g, and the number of viable bacteria of Bacillus amyloliquefaciens was 6.1×10 8 Before use, mix 0.5 parts of the composite bacteria, 0.5 parts of brown sugar and 10 parts of warm water at 35°C evenly, let it stand for 30 minutes to activate, and then obtain the activated composite bacteria solution for use.

[0037] S2. Add 54 parts of water to the first mixture obtained in S1 to obtain a second mixture, and place the second mixture in a fermentation tank for sealed fermentation. The pile has a trapezoidal cross-section, the fermentation temperature is 50-60° C., the pile is turned once every 72 hours, and the fermentation cycle is 18 days, until the material becomes dark brown, has no ammonia odor, and is covered with white mycelium to obtain a fermented product.

[0038] S3. Use a belt dryer to dry the fermented material obtained in S2, with an air inlet temperature of 75±5°C, a material layer thickness of about 4 cm, and a moisture content of about 10% after drying. Then use a rotary drum granulator to granulate the material at a speed of 20 rpm and an inclination angle of 45° to obtain organic fertilizer granules with a particle size of 3-5 mm in diameter.

[0039] S4. Add the organic fertilizer particles into a coating machine, spray the coating liquid onto the surface of the organic fertilizer particles through a spray gun, wherein the coating material accounts for 3.5% of the mass of the organic fertilizer particles, the atomization pressure is 0.25 MPa, and hot air is introduced to evaporate the water. The hot air temperature is 55° C. and the wind speed is 1.8 m / s. The fluidized bed is cooled to 30° C. and sieved to obtain the agricultural waste bio-organic fertilizer.

[0040] Example 2: This example differs from Example 1 in that a coating solution is prepared by mixing the coating material and water in a mass ratio of 3:20. The coating material is prepared by mixing, by mass, 80 parts of modified hydroxypropyl methylcellulose, 3 parts of polyvinyl alcohol, 5 parts of magnesium aluminum hydrotalcite, and 4 parts of citric acid.

[0041] Example 3: This example differs from Example 1 in that a coating solution is prepared by mixing the coating material and water in a mass ratio of 4:20. The coating material is prepared by mixing, by mass, 85 parts of modified hydroxypropyl methylcellulose, 5 parts of polyvinyl alcohol, 8 parts of magnesium aluminum hydrotalcite, and 5 parts of citric acid.

[0042] Example 4: This example differs from Example 1 in that a coating solution is prepared by uniformly mixing the coating material and water in a mass ratio of 3.8:20. The coating material is prepared by uniformly mixing, by mass, 81 parts of modified hydroxypropyl methylcellulose, 4.2 parts of polyvinyl alcohol, 6 parts of magnesium aluminum hydrotalcite, and 5 parts of citric acid.

[0043] Comparative Example 1: The difference between this comparative example and Example 1 is that in the preparation of the coating material, modified hydroxypropyl methylcellulose is replaced by hydroxypropyl methylcellulose; and magnesium aluminum hydrotalcite powder is not added.

[0044] Specifically, the coating material is prepared as follows: by weight, 83 parts of hydroxypropyl methylcellulose, 4 parts of polyvinyl alcohol and 4.5 parts of citric acid are mixed evenly to obtain the coating material.

[0045] 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.

[0046] Specifically, the coating material is prepared as follows: by weight, 83 parts of modified hydroxypropyl methylcellulose, 4 parts of polyvinyl alcohol and 4.5 parts of citric acid are mixed evenly to obtain the coating material.

[0047] Comparative Example 3: The difference between this comparative example and Example 1 is that in the preparation of the coating material, modified hydroxypropyl methylcellulose is replaced by hydroxypropyl methylcellulose.

[0048] Specifically, the coating material is prepared as follows: by weight, 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 to obtain the coating material.

[0049] Test example: with reference to GB / T 23348-2009, the agricultural waste bio-organic fertilizer of Example 1-Example 4 and Comparative Example 1-Comparative Example 3 was prepared and the cumulative nutrient release rate was measured. The characterization object was the total nitrogen release rate. Test method: 20g of organic fertilizer (weighed to 0.01g) was weighed and placed in a small bag made of 100-mesh nylon gauze. After sealing, the small bag was placed in a 500mL glass bottle, 400mL of distilled water was added, the bottle was sealed with a lid, and the bottle was placed in a 25°C biochemical constant temperature incubator. The sampling time was 1d, 3d, 7d, 14d, 28d, and 56d. Sampling was stopped when the cumulative nutrient release rate reached 80%. During sampling, the bottle was turned upside down three times to make the liquid concentration in the bottle consistent. Test results: see Table 1.

[0050] Table 1. Test example data

[0051]

[0052] Result analysis: Combining the data in Table 1 and Figure 1 By analyzing Examples 1 to 4 and Comparative Examples 1 to 3, it can be seen that the agricultural waste bio-organic fertilizer prepared by the present invention (Examples 1 to 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.

[0053] A specific analysis of Comparative Examples 1 and 2 shows that, compared to Comparative Example 1 (which does not contain magnesium-aluminum hydrotalcite), Comparative Example 2 uses the raw material hydroxypropyl methylcellulose of the coating material to make the modified hydroxypropyl methylcellulose of the present invention, and as a result, the speed at which the agricultural waste bio-organic fertilizer releases nutrients is significantly accelerated. This shows that when hydroxypropyl methylcellulose is made into the modified hydroxypropyl methylcellulose of the present invention alone, the rate at which the agricultural waste bio-organic fertilizer finally releases nutrients is accelerated, resulting in a shortened stable nutrient release cycle.

[0054] This is mainly because the modified hydroxypropyl methylcellulose generated by esterification forms a three-dimensional gel network after absorbing water, which can delay the diffusion of nutrients and reduce the fertilizer efficiency / nutrient release rate. However, citric acid in the coating solution will dissolve preferentially in a humid environment, and its acidity (pH≈2.1) can catalyze the hydrolysis of ester bonds, which will lead to the premature disintegration of the gel network. That is, the catalytic hydrolysis rate of citric acid is greater than the gel network barrier effect, resulting in the fertilizer efficiency / nutrient release rate not decreasing but increasing, and the stable nutrient release period is shortened.

[0055] Specifically analyze comparative example 1 and comparative example 3, it is known that, compared to comparative example 1, increase magnesium aluminum hydrotalcite in the raw material of comparative example 3 coating materials, the speed that result makes agricultural waste bio-organic fertilizer release nutrient obviously slows down.Show that increase magnesium aluminum hydrotalcite in the raw material components of coating materials, can make the speed that finally makes agricultural waste bio-organic fertilizer release nutrient slow down.Carry out specific analysis again in conjunction with embodiment 1, it is known that increase magnesium aluminum hydrotalcite in the raw material components of coating materials, and raw material hydroxypropyl methylcellulose is made modified hydroxypropyl methylcellulose of the present invention, the two can produce synergistic effect, collaboratively reduce the nutrient release speed that finally makes agricultural waste bio-organic fertilizer, and then extend the nutrient stable release cycle.

[0056] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0057] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing agricultural waste bio-organic fertilizer, characterized in that: The following steps are involved: S1. Mixing, by mass, 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 the composite bacterial strain to obtain a first mixture; S2. Add 50-55 parts of water to the first mixture obtained in S1 to obtain a second mixture, and place the second mixture in a fermentation tank for sealed fermentation to obtain a fermentation product; S3, drying the fermented product obtained in S2, and then granulating it using a granulator to obtain organic fertilizer granules; S4, adding the organic fertilizer particles into a coating machine, spraying the coating liquid onto the surface of the organic fertilizer particles through a spray gun, passing hot air to evaporate the water, cooling, and sieving to obtain the agricultural waste bio-organic fertilizer; The coating liquid comprises water and a coating material, wherein the coating material comprises, by mass, 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.

2. The method for preparing agricultural waste bio-organic fertilizer according to claim 1, wherein The preparation method of the modified hydroxypropyl methylcellulose is as follows: A1. Dissolve hydroxypropyl methylcellulose in 1,4-dioxane to obtain a first solution, wherein the ratio of hydroxypropyl methylcellulose to 1,4-dioxane is 1 g:45-50 mL; A2, adding phthalic anhydride, triethylamine catalyst and toluene to the first solution obtained in A1, with a mass ratio of phthalic anhydride to hydroxypropyl methylcellulose of 0.85:1, and reacting at a temperature of 85±2°C for 4-5 hours, and dehydrating through a toluene-water azeotrope to obtain a reaction solution; A3. Cool the reaction solution obtained in A2 to 30°C, add deionized water dropwise at a rate of 40 mL / min with stirring to precipitate a flocculent precipitate. The mass ratio of deionized water to hydroxypropyl methylcellulose is (18-22):1; A4. Filter the precipitate obtained in A3 and rinse with deionized water until the filtrate has a pH of 6.5-7.

0. The solid is vacuum-dried at 55° C. and −0.08 MPa for 5-6 h to obtain modified hydroxypropyl methylcellulose.

3. The preparation method of agricultural waste bio-organic fertilizer according to claim 2, 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.

4. The method for preparing agricultural waste bio-organic fertilizer according to claim 1, wherein In S1, the agricultural waste is crop straw; the composite bacteria include Bacillus subtilis and Bacillus amyloliquefaciens, and the number of viable bacteria is ≥ 500 million / g.

5. The method for preparing agricultural waste bio-organic fertilizer according to claim 1, wherein In S2, the fermentation temperature is 50-60°C, the fermentation period is 15-20 days, and the pile is turned once every 72 hours.

6. The method for preparing agricultural waste bio-organic fertilizer according to claim 1, wherein In S4, the atomization pressure is 0.2-0.3 MPa, the hot air temperature is ≤60°C; and the coating material accounts for 3.2%-4.0% of the mass of the organic fertilizer particles.

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

20.

8. An agricultural waste bio-organic fertilizer, characterized in that: The method is as described in any one of claims 1 to 7.

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