Preparation method of anaerobic self-chelating organic water-soluble fertilizer

Abstract

The invention discloses a preparation method of an anaerobic self-chelating organic water-soluble fertilizer, and belongs to the technical field of agricultural organic water-soluble fertilizer preparation. The method comprises the following steps: crushing and tempering organic wastes, mixing the organic wastes with a nano confinement carrier with specific pore sizes and surface functional groups, and constructing a biological membrane in an anaerobic reactor; then carrying out mineralization reaction, automatically triggering a self-chelation reconstruction program by monitoring the concentration of short-chain fatty acid on line, and carrying out directional chelation and self-assembly on endogenous metabolites and nutrient ions in a nano confinement space under the guidance of a carrier; and finally, separating, sterilizing and concentrating to obtain a finished product. On the premise of not depending on an exogenous chelating agent, the organic-inorganic composite nano fertilizer with the average particle size being 80-150 nm, the proportion of chelated zinc being larger than or equal to 82% and the proportion of chelated phosphorus being larger than or equal to 68% is prepared, the 30-day nitrogen and phosphorus leaching rates of the organic-inorganic composite nano fertilizer are lower than 17.0% and 11.5% respectively, and the organic-inorganic composite nano fertilizer has good slow release performance and agricultural yield increasing effect and has good application prospects. And a brand new technical approach is provided for high-value resource utilization of organic wastes.

Description

Technical Field

[0001] This invention belongs to the field of agricultural organic water-soluble fertilizer preparation technology, specifically, it relates to a method for preparing anaerobic self-chelating organic water-soluble fertilizer. Background Technology

[0002] Within the framework of sustainable development in modern agriculture, the efficient resource utilization of organic waste is crucial for constructing an ecological cycle and efficient fertilization system. Livestock manure, straw, and food processing byproducts are rich in nitrogen, phosphorus, potassium, and various trace elements; however, these nutrients are mostly contained within complex organic macromolecules, resulting in slow natural degradation and low bioavailability. While traditional composting technologies can achieve partial stabilization, they still suffer from long cycles, uncoordinated nutrient release, and easy nutrient loss, making it difficult to meet the comprehensive needs of precision agriculture for rapid, slow-release, and environmentally friendly fertilizers.

[0003] Anaerobic bioconversion technology has become a mainstream treatment method due to its ability to simultaneously achieve organic matter degradation, nitrogen stabilization, and energy recovery. To further improve the availability of phosphorus, potassium, and trace elements, the industry has attempted to add exogenous chelating agents (such as EDTA, humates, or synthetic polymers). However, this strategy still faces significant bottlenecks in industrial applications: introducing exogenous chelating agents not only increases costs and process complexity, but some compounds (such as EDTA) also pose ecotoxicity and residue risks, contradicting the concept of green development; furthermore, chelation reactions are often independent of the initial mineralization process, and their efficiency is significantly limited by ion concentration and diffusion, making it difficult to achieve efficient and targeted chelation assembly. Even using lactic acid fermentation to produce natural chelating agents, as described in Japanese Patent JP2008023523A, is still a non-directional side reaction, lacking effective control over the morphology, structure, and stability of the product, and failing to meet the requirements of high-end water-soluble fertilizers in terms of chelation efficiency, slow-release performance, and nano-uniformity.

[0004] Essentially, existing technologies suffer from a fundamental contradiction between "process fragmentation" and "structural disorder": microbial mineralization pursues widespread degradation of organic matter and ion release, with random and dispersed reactions; while efficient chelation requires the orderly assembly and fixation of molecules and ions in a local microenvironment. These two aspects are inherently conflicting in terms of thermodynamics and spatial organization. The lack of a mediating mechanism for the synergistic regulation of biological reactions and self-assembly at the nanoscale makes it difficult to simultaneously achieve high mineralization rates and high chelation rates, as well as high ion concentrations and high structural stability.

[0005] Therefore, the current core technical challenge lies in how to construct, without relying on exogenous chelating agents and engineered strains, a nano-confined system with both biocatalytic enhancement and molecular template induction functions in situ within an anaerobic reactor through material design and microenvironment regulation. This system would achieve spatiotemporal coupling and structural guidance of microbial mineralization and molecular self-assembly, ultimately forming an organic-inorganic composite with regular nanomorphology, narrow particle size distribution, high chelation efficiency, and excellent sustained-release performance. Summary of the Invention

[0006] To achieve the above-mentioned objectives, the present invention employs the following technical solution:

[0007] This invention provides a method for preparing anaerobic self-chelating organic water-soluble fertilizer, comprising the following steps:

[0008] (a) Raw material pretreatment: crush livestock and poultry manure, crop straw or food processing by-products to a maximum particle size of no more than 1.0 mm, and adjust the material moisture content to 83%–87% and the carbon-nitrogen ratio to 18:1–22:1;

[0009] (b) Carrier blending and biofilm construction: The material obtained in step (a) is uniformly mixed with a nano-confined carrier at a dry weight ratio of 5%–15%, wherein the nano-confined carrier is a porous material with a pore size of 20–80 nm and surface functional groups; the mixture is then placed in an anaerobic reactor and cultured for 3–7 days at a temperature of 30–40 °C, pH 6.5–7.5 and redox potential below -300 mV to form a stable biofilm;

[0010] (c) Anaerobic mineralization and self-chelation reconstruction: Maintain an anaerobic environment, control the system temperature at 35–45℃ and the pH at 6.8–7.2 to carry out the mineralization reaction; monitor the concentration of short-chain fatty acids in the reaction system using an online near-infrared spectrometer, and when the total amount reaches 2000–3000 mg / L, automatically trigger the carrier-guided in-situ self-chelation reconstruction program, adjust the system pH to 6.0–7.0, and raise the temperature to 40–55℃, so as to promote the directional chelation and self-assembly of endogenous microbial metabolites and mineralized nutrient ions in the functional group guidance and nano-confined space of the nano-confined carrier, with a total reaction time of 15–25 days;

[0011] (d) Post-processing of the product: The reaction liquid obtained in step (c) is subjected to solid-liquid separation, the liquid phase is collected and sterilized and concentrated to obtain the organic water-soluble fertilizer rich in organic-inorganic composite nanoparticles.

[0012] Furthermore, the nano-confined carrier is selected from modified bio-carbon, amino-modified mesoporous silica, and carboxyl-functionalized polymer composite porous materials.

[0013] Furthermore, the nano-confined carrier is modified biochar, which is prepared by anaerobic carbonization of rice husks at 600℃, followed by impregnation in a phosphoric acid solution at a mass ratio of 1:2 for 24 hours, activation at 500℃, washing, and drying. Its pore size is 20–50 nm, and its specific surface area is 520–680 m². 2 / g, with a surface carboxyl group density of 0.9–1.3 mmol / g.

[0014] Furthermore, the nano-confined support is amino-modified mesoporous silica, which is obtained by hydrolysis and condensation of tetraethyl orthosilicate as the silicon source and CTAB as the template in an ammonia solution at pH=11. After aging, washing, and calcination at 550°C, a mesoporous silica matrix is ​​obtained, which is then reacted with a 5wt% solution of 3-aminopropyltriethoxysilane toluene under reflux at 80°C. After washing and drying, the resulting matrix has an amino density of 0.8–1.1 mmol / g and a pore volume of 1.2–1.6 cm³. 3 / g.

[0015] Furthermore, the nano-confined carrier is a carboxyl-functionalized polymer composite porous material, which is prepared by blending polyvinyl alcohol and sodium alginate in a mass ratio of 3:1, followed by freeze molding, glutaraldehyde crosslinking, and succinic anhydride carboxylation modification. Its pore size is 30–80 nm and its carboxyl density is 1.2–1.6 mmol / g.

[0016] Furthermore, in step (b), during the biofilm construction stage, trace element solutions are continuously added to the system to achieve the following final concentrations: Ni 2 ⁺ 0.05–0.15 mg / L, Co 2 ⁺ 0.03–0.07 mg / L, Fe 2 ⁺ 0.1–0.3 mg / L.

[0017] The present invention also provides an organic water-soluble fertilizer prepared by the method described above; the water-soluble fertilizer contains organic-inorganic composite nanoparticles, the average particle size of the nanoparticles is 80–150 nm, and the polydispersity index (PDI) is ≤0.19; and, by mass concentration, the proportion of chelated zinc in the water-soluble fertilizer is ≥82% of the total zinc, and the proportion of chelated phosphorus in the total water-soluble phosphorus is ≥68%.

[0018] Furthermore, the organic water-soluble fertilizer, by mass concentration, has a total nitrogen content of 35–55 g / L, a water-soluble phosphorus content of 40–60 g / L, a water-soluble potassium content of 50–80 g / L, and a total chelated trace element content of not less than 5 g / L.

[0019] Beneficial effects:

[0020] (1) This invention guides the directional self-assembly of endogenous microbial metabolites and mineralized nutrient ions within a confined space using a nano-confined carrier, successfully achieving in-situ efficient chelation of nutrients. Examples show that the final product contains 82.5%–87.1% chelated zinc and 68.7%–74.2% chelated phosphorus, respectively, without the need for exogenous chelating agents such as EDTA. This avoids chemical residues and potential ecological risks at the source, aligning with the development requirements of green agriculture.

[0021] (2) This invention couples two traditionally separate processes: microbial mineralization and molecular self-chelation. By using online monitoring of short-chain fatty acid concentration as a trigger signal, the reconstruction program is intelligently initiated, so that the release and fixation of nutrients are carried out simultaneously. This solves the technical contradiction that it is difficult to achieve both high mineralization rate and high chelation rate, and improves process efficiency and controllability.

[0022] (3) Under the synergistic effect of the carrier functional groups and the nano-confined space, the final product of this invention forms well-structured organic-inorganic composite nanoparticles with an average particle size of 80–150 nm and uniform distribution (PDI≤0.19). This nanostructure endows the product with good sustained-release performance, with cumulative nitrogen and phosphorus leaching rates as low as 13.8%–17.0% and 9.3%–11.5% after 30 days, respectively, which are significantly higher than those of products from traditional processes, effectively reducing nutrient loss and improving utilization efficiency.

[0023] (4) The product of this invention not only has a high content of chelated trace elements, but also meets the standards of commercial water-soluble fertilizers for the content of total nitrogen (35–55 g / L), water-soluble phosphorus (40–60 g / L), and water-soluble potassium (50–80 g / L). It combines fast-acting nutrients with slow-release micronutrients, and can meet the nutrient needs of crops throughout their entire growth period. Pot experiments have confirmed that the application of this product can significantly promote tomato growth and improve yield and quality.

[0024] (5) This invention transforms organic waste such as livestock and poultry manure and straw into high-value-added nanostructured water-soluble fertilizer. The process route is green and efficient, which not only solves the problem of waste treatment, but also turns waste into treasure, creates economic value, and provides strong technical support for the sustainable development of agriculture. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solutions of this invention, the present application will be further described in detail below with reference to embodiments.

[0026] Example 1: Using modified biochar as a carrier

[0027] 1. Raw material pretreatment: Take 100 kg of chicken manure and wheat straw (mass ratio 3:1) (dry weight). Crush them with a hammer mill to a maximum particle size ≤1.0 mm. Transfer to a conditioning tank, add deionized water to adjust the moisture content to 83%, and add urea to adjust the carbon-nitrogen (C / N) ratio to 22:1 to obtain a uniform paste material.

[0028] 2. Preparation of modified biochar: Rice husks were used as a precursor and carbonized at 600°C for 2 hours under an anaerobic atmosphere with a heating rate of 5°C / min. The carbonized product was mixed with 85% phosphoric acid at a mass ratio of 1:2 and impregnated for 24 hours, followed by activation at 500°C for 1 hour (heating rate of 10°C / min). After repeated washing with deionized water until the pH of the washing solution was neutral, the product was dried at 80°C for 12 hours to obtain a pore size of 30 nm (measured using a BET (Brunauer-Emmett-Teller) adsorption instrument) and a specific surface area of ​​660 m². 2 Modified biochar with a surface carboxyl density of 1.15 mmol / g (measured by BET adsorption) and a surface carboxyl density of 1.15 mmol / g (measured by Fourier transform infrared spectroscopy).

[0029] 3. Carrier Blending and Biofilm Construction: The pretreated material obtained in step 1 and 5 kg (dry weight, accounting for 5% of the dry weight of the pretreated material) of the modified biochar carrier prepared in step 2 were added to a biaxial mixer and mixed at 30 rpm for 25 minutes until uniformly dispersed. The mixture was transferred to a 50 L anaerobic reactor and cultured for 7 days at a temperature of 40℃, pH 7.5, and redox potential (ORP) of -320 mV to form a stable biofilm. During this period, trace element solution was continuously added to maintain the Ni content in the system. 2 ⁺、Co 2 ⁺、Fe 2 The concentrations of ⁺ were maintained at 0.05 mg / L, 0.03 mg / L, and 0.1 mg / L, respectively.

[0030] 4. Anaerobic mineralization and self-chelation reconstruction: First, the mineralization step is carried out: maintaining an anaerobic environment, adjusting the temperature to 35℃ and the pH to 7.2, the mineralization reaction is initiated. Then, the self-chelation reconstruction program is started: the concentration of short-chain fatty acids in the reaction system is monitored using an online near-infrared spectrometer. When the total concentration reaches 2000 mg / L (day 10), the reconstruction program is triggered: the pH is automatically adjusted to 7.0, the temperature is raised to 40℃, the stirring speed is adjusted to 30 rpm, and the reaction continues for a total cycle of 25 days.

[0031] 5. Post-processing of the product: After the reaction is completed, solid-liquid separation is performed by a horizontal screw centrifuge (2500 rpm, 12 min) to obtain a crude liquid phase, which is then filtered through a 0.2 μm ceramic membrane in a cross-flow manner (transmembrane pressure difference (TMP) 0.15 MPa). The filtrate is then sterilized briefly at 125℃ (10 s) and concentrated at 50℃ and -0.09 MPa to a total nutrient concentration of 205 g / L to obtain the finished organic water-soluble fertilizer A.

[0032] Example 2: Using amino-modified mesoporous silica as a carrier

[0033] 1. Raw material pretreatment: Take 100 kg of pig manure and corn stalks (mass ratio 2:1) (dry weight). Crush them with a hammer mill until the maximum particle size is ≤1.0 mm. Transfer to a conditioning tank, add deionized water to adjust the moisture content to 85%, and add urea to adjust the carbon-nitrogen (C / N) ratio to 20:1 to obtain a uniform paste material.

[0034] 2. Preparation of amino-modified mesoporous silica: Tetraethyl orthosilicate (TEOS) was used as the silicon source, and hexadecyltrimethylammonium bromide (CTAB) was used as the template agent. The mixture was hydrolyzed and condensed in an ammonia solution at pH 11, with a mass ratio of TEOS, CTAB, and water of 1:0.3:10. After aging for 24 hours, washing with deionized water until no CTAB residue remained, and calcining at 550°C for 4 hours, a mesoporous silica matrix was obtained. This matrix was then refluxed at 80°C for 6 hours with a 5% (w / w) solution of 3-aminopropyltriethoxysilane-toluene (10 times the mass of the mesoporous silica matrix). After washing three times with anhydrous ethanol and drying at 60°C for 12 hours, a surface amino density of 0.95 mmol / g (measured using Fourier transform infrared spectroscopy) and a pore volume of 1.4 cm³ were obtained. 3 / g (measured using a BET adsorption analyzer) of the product.

[0035] 3. Carrier Blending and Biofilm Construction: The pretreated material obtained in step 1 and 10 kg (dry weight, accounting for 10% of the dry weight of the pretreated material) of the amino-modified mesoporous silica carrier prepared in step 2 were added to a biaxial mixer and mixed at 30 rpm for 25 minutes until uniformly dispersed. The mixture was transferred to a 50 L anaerobic reactor and cultured for 5 days at 35 °C, pH 7.0, and ORP -350 mV to form a stable biofilm. During this period, trace element solution was continuously added to maintain the Ni content in the system. 2 ⁺、Co 2 ⁺、Fe 2 The concentrations of ⁺ were maintained at 0.10 mg / L, 0.05 mg / L, and 0.2 mg / L, respectively.

[0036] 4. Anaerobic mineralization and self-chelation reconstruction: First, the mineralization step is carried out: maintain the anaerobic environment, adjust the temperature to 40℃ and the pH to 7.0, and proceed with the mineralization reaction. Then, the self-chelation reconstruction program is initiated: when the total amount of short-chain fatty acids detected by the online near-infrared spectrometer reaches 2500 mg / L (day 8), the carrier-guided in-situ self-chelation reconstruction program is automatically triggered: automatically adjust the pH to 6.5, raise the temperature to 47℃, adjust the stirring speed to 30 rpm, and continue the reaction for a total cycle of 20 days.

[0037] 5. Post-processing of the product: Same as in Example 1, after concentration, the finished organic water-soluble fertilizer B is obtained with a total nutrient concentration of 215g / L.

[0038] Example 3: Using carboxyl-functionalized polymer composite porous materials as carriers

[0039] 1. Raw material pretreatment: Take 100 kg of soybean residue and mushroom residue (mass ratio 1:1) (dry weight). Crush them to a maximum particle size ≤1.0 mm. Adjust the moisture content to 87% and the C / N ratio to 18:1.

[0040] 2. Preparation of carboxyl-functionalized polymer composite porous material: Polyvinyl alcohol (molecular weight 85000) and sodium alginate were mixed at a mass ratio of 3:1 to prepare an aqueous solution with a mass fraction of 10%. Sodium bicarbonate was added as a pore-forming agent at a mass ratio of 5% of the total mass of the aqueous solution. The composite porous material was obtained after freezing at -20°C for 12 hours, replacing it with tert-butanol (5 times the volume of the frozen material) for 24 hours, and freeze-drying for 48 hours. The material was then crosslinked with a 2.5% glutaraldehyde solution (20 times the mass of the freeze-dried composite porous material) at room temperature (25°C) for 4 hours. Next, it was carboxylated with a 5% succinic anhydride dimethylformamide (DMF) solution (15 times the mass of the crosslinked material) at 60°C for 3 hours. Finally, it was repeatedly washed with deionized water until no residual reagents were found, and dried at 40°C for 24 hours to obtain a porous material with a pore size of 60 nm (measured by BET adsorption) and a carboxyl density of 1.3 mmol / g (measured by Fourier transform infrared spectroscopy).

[0041] 3. Carrier Blending and Biofilm Construction: The pretreated material obtained in step 1 and 15 kg (dry weight, accounting for 15% of the dry weight of the pretreated material) of the carboxyl-functionalized polymer composite porous material carrier prepared in step 2 were added to a biaxial mixer and mixed at 30 rpm for 25 minutes until uniformly dispersed. The mixture was then transferred to a 50 L anaerobic reactor and cultured for 3 days at 30 °C, pH 6.5, and ORP -380 mV to form a stable biofilm. During this period, trace element solution was continuously added to maintain the Ni content in the system. 2 ⁺、Co 2 ⁺、Fe 2 The concentrations of ⁺ were maintained at 0.15 mg / L, 0.07 mg / L, and 0.3 mg / L, respectively.

[0042] 4. Anaerobic mineralization and self-chelation reconstruction: First, the mineralization step is carried out: maintain the anaerobic environment, adjust the temperature to 45℃ and the pH to 6.8, and proceed with the mineralization reaction. Then, the self-chelation reconstruction program is initiated: when the total amount of short-chain fatty acids detected by the online near-infrared spectrometer reaches 3000 mg / L (day 5), the carrier-guided in-situ self-chelation reconstruction program is automatically triggered: automatically adjust the pH to 6.0, raise the temperature to 55℃, adjust the stirring speed to 30 rpm, and continue the reaction for a total cycle of 15 days.

[0043] 5. Post-processing of the product: Same as in Example 1, after concentration, the finished organic water-soluble fertilizer C is obtained with a total nutrient concentration of 198g / L.

[0044] Comparative Example 1: No nano-confined carrier (including nano-confined carriers as defined in this invention, such as modified biochar, amino-modified mesoporous silica, or carboxyl-functionalized polymer composite porous materials)

[0045] The preparation steps for this comparative example are exactly the same as in Example 2, the only difference being that no nano-confined carrier (modified biochar, amino-modified mesoporous silica, or carboxyl-functionalized polymer composite porous material) is added. During the reaction, the microorganisms exist in a free state or in the form of simple flocs, and cannot construct a nano-confined space. The final product is liquid fertilizer D.

[0046] Comparative Example 2: Ordinary carrier (unmodified activated carbon)

[0047] The preparation steps for this comparative example are exactly the same as those in Example 1, the only difference being that an equal amount of commercially available unmodified activated carbon (specific surface area 550 m²) was used. 2 / g, but with few surface functional groups and a carboxyl density <0.2mmol / g) to replace the modified biocarbon carrier. The final product is liquid fertilizer E.

[0048] Comparative Example 3: Exogenous Addition of EDTA Chelating Agent

[0049] The preparation steps for this comparative example are exactly the same as the first half of Example 2 (including the use of an amino-modified mesoporous silica support and the anaerobic mineralization process). The difference is that after the mineralization reaction, the self-chelation reconstruction process is not initiated. Instead, disodium ethylenediaminetetraacetate (EDTA disodium salt) is directly added exogenously to the reaction system, allowing EDTA disodium salt to chelate with all chelateable metal ions in the system (mainly Zn). 2 ⁺、Fe 2 ⁺、Mn 2 ⁺、Cu 2 The total molar ratio of ⁺ was 1.2:1. The mixture was stirred for 2 hours to induce chelation, followed by further post-processing. The final product was liquid fertilizer F.

[0050] Effect Experiments and Data Analysis

[0051] 1. Conduct biocompatibility testing (toxicity assessment) on the nano-confined carrier.

[0052] The effect of carrier materials on the activity of anaerobic microorganisms was determined using the MTT assay (3-(4,5-dimethylthiazol-2)-2,5-diphenyltetrazolium bromide). After co-culturing the extracts of each carrier with enriched endogenous anaerobic microorganisms for 4 hours, the relative cell viability and inhibition rate were measured.

[0053] 2. Conduct microbial adhesion tests (enrichment capacity assessment) on the nano-confined carrier.

[0054] The adhesion ability of microorganisms to the carrier surface was quantified using plate counting. The sterilized carrier material was then mixed with a microbial suspension (1×10⁻⁶). 7 After co-culturing (CFU / mL) under anaerobic conditions for 24 hours, the amount of microorganisms attached to the carrier surface was counted by ultrasonic peeling and plate counting.

[0055] 3. The organic water-soluble fertilizers A, B, and C prepared in Examples 1-3 of this invention, as well as the organic water-soluble fertilizers D, E, and F prepared in Comparative Examples 1-3, were subjected to product performance testing and agricultural effect verification.

[0056] (1) Average particle size / polydispersity index (PDI)

[0057] The sample was diluted to a suitable concentration and placed in a dedicated sample cell. Dynamic light scattering (DLS) was used to irradiate the nanoparticles with a helium-neon laser with a wavelength of 633 nm, causing scattering. The fluctuation rate of the scattered light intensity was analyzed by a detector, and the hydrodynamic particle size distribution and PDI (polydispersity index) value were calculated using the Stokes-Einstein equation to characterize the width of the particle size distribution.

[0058] (2) Percentage of chelated zinc / Percentage of chelated phosphorus

[0059] A certain amount of sample was taken and centrifuged at high speed using an ultrafiltration centrifuge tube with a molecular weight cutoff of 3 kDa. Free ions could pass through the ultrafiltration membrane into the filtrate, while chelated macromolecular complexes were retained in the concentrate. The filtrate and retentate were collected separately, and the elemental concentrations of zinc or phosphorus in the two parts were accurately determined using inductively coupled plasma optical emission spectrometry (ICP-OES). The chelation rate was calculated by determining the proportion in the retentate.

[0060] (3) Nitrogen / phosphorus leaching rate over 30 days

[0061] A quantitative amount of air-dried soil, passed through a 2mm sieve, was weighed according to the standard bulk density (1.2 g / cm³). 3 The test fertilizer, containing equal amounts of nitrogen (1.0 g) and phosphorus (0.5 g), was packed into a PVC leaching column with an inner diameter of 5 cm and a height of 30 cm. The fertilizer was mixed with the top 5 cm of soil. A daily amount (20 mL) of deionized water was added to simulate rainfall, and the leachate was collected and measured daily. After 30 days of leaching, specific nutrient ions (NH4⁺, NO3⁻, PO4⁻) in all leachates were determined using ion chromatography (IC) or molybdenum-antimony spectrophotometry (for phosphorus determination). 3 ⁻) Total amount, calculate its percentage relative to the total amount of nutrients applied, which is the cumulative leaching rate.

[0062] (4) Total nitrogen content

[0063] The sample was digested in concentrated sulfuric acid to convert organic nitrogen and ammonium nitrogen into ammonium sulfate. After alkalization, ammonia was distilled off, absorbed with boric acid solution, and finally titrated with standard hydrochloric acid solution to calculate the total nitrogen content.

[0064] (5) Water-soluble phosphorus content

[0065] After extraction with water, the sample reacted with molybdate and metavanadate under acidic conditions to form a yellow vanadium-molybdate phosphate complex. The absorbance was measured at 420 nm and quantified using a standard curve.

[0066] (6) Water-soluble potassium content

[0067] The sample solution is atomized and sprayed into a high-temperature flame. Potassium is excited and emits characteristic light with a wavelength of 766.5 nm. The intensity of the light is proportional to the potassium content, and the quantity is determined by detecting the light intensity.

[0068] (7) Total amount of chelated trace elements

[0069] The total amount of chelated trace elements is the sum of the contents of chelated Zn, Fe, Mn, Cu, etc. After appropriate dilution or acid digestion, the sample is directly injected. The elements are atomized and excited by high temperature using inductively coupled plasma (ICP), and the emission intensity of each trace element is detected simultaneously by measuring the emission intensity at the characteristic wavelength.

[0070] The test results of the products prepared in Examples 1-3 and Comparative Examples 1-3 are summarized in Table 3.

[0071] 4. Pot experiment verification

[0072] A pot experiment was conducted using tomato (variety: 'Jinfen No. 1') as the test crop. Each treatment group had 10 replicates (n=10, where n represents the number of biological replicates), and the growth period was 60 days. Biological traits at harvest were measured, and the results are shown in Table 4.

[0073] Table 1. Biocompatibility test results of the carriers used in Examples 1-3

[0074] carrier type Relative survival rate (%) Inhibition rate (%) Modified biochar 98.2 ± 1.5 1.8 ± 1.5 Amino-modified mesoporous silica 96.5 ± 1.8 3.5 ± 1.8 Carboxyl-functionalized polymer composite porous materials 97.8 ± 1.2 2.2 ± 1.2 Blank control 100.0 0.0

[0075] The data in Table 1 show that the inhibition rates of the three carriers were all below 4%, confirming that they had no significant toxic effects on microbial growth.

[0076] Table 2. Test results of microbial adhesion amount of the carriers used in Examples 1-3

[0077] carrier type <![CDATA[Microbial attachment amount (CFU / cm 2 )]]> Modified biochar <![CDATA[(6.8 ± 0.5)× 10 7 ]]> Amino-modified mesoporous silica <![CDATA[(5.2 ± 0.4)× 10 7 ]]> Carboxyl-functionalized polymer composite porous materials <![CDATA[(7.1 ± 0.6)× 10 7 ]]> Blank control (smooth surface) <![CDATA[(3.2 ± 0.3)× 10 5 ]]>

[0078] The data in Table 2 show that the adhesion amount of all three carriers reached 10.7 CFU / cm 2 The magnitude was significantly higher than that of the blank control, demonstrating that its porous structure and surface functional groups can effectively promote microbial attachment.

[0079] Table 3 Comparison of Product Performance Indicators (corresponding to Examples 1-3 and Comparative Examples 1-3)

[0080] detection indicators Fertilizer A Fertilizer B Fertilizer C Fertilizer D Fertilizer E Fertilizer F Average particle size (nm) 148 115 82 ＞1000 305 185 PDI 0.18 0.16 0.15 0.45 0.32 0.28 Percentage of chelated Zn (%) 82.5 85.3 87.1 15.2 35.8 92.5 Percentage of chelated P (%) 68.7 71.5 74.2 8.5 22.1 70.8 30-day nitrogen leukopenia rate (%) 17.0 15.1 13.8 48.5 36.2 25.7 30-day P urination rate (%) 11.5 10.2 9.3 42.1 30.5 16.4 Total nitrogen content (g / L) 48.5 52.1 46.8 32.5 38.2 44.7 Water-soluble phosphorus content (g / L) 52.3 58.6 49.7 36.8 42.5 55.2 Water-soluble potassium content (g / L) 68.4 75.2 65.9 51.3 58.7 70.5 Total amount of chelated trace elements (g / L) 5.8 6.5 5.2 1.5 2.8 5.8

[0081] As shown in Table 3, the average particle size distribution of the products prepared in Examples 1-3 is in the range of 82-148 nm, and the polydispersity index (PDI value) is all below 0.19, indicating that this method can form nanoparticles with uniform particle size distribution. In contrast, the product of Comparative Example 1, which lacks a nano-confined support, exhibits macroscopic flocculation, while the product of Comparative Example 2, which uses a common support, has a relatively wide particle size distribution.

[0082] The chelated zinc content of the products in Examples 1-3 reached 82.5%-87.1%, and the chelated phosphorus content reached 68.7%-74.2%, demonstrating that this method can achieve effective nutrient fixation without relying on exogenous chelating agents. Although Comparative Example 3 achieved a high zinc chelation rate (92.5%) by adding EDTA, its phosphorus chelation rate (70.8%) was relatively limited. Furthermore, this method introduced an exogenous chemical chelating agent (EDTA), posing an ecotoxicity risk and failing to meet the requirements of green agriculture.

[0083] In the 30-day leaching test, the nitrogen leaching rate of the products in Examples 1-3 was 13.8%-17.0%, and the phosphorus leaching rate was 9.3%-11.5%, which was lower than that of the comparative groups. This indicates that the fertilizer products obtained by this method have better nutrient retention capacity.

[0084] The total nitrogen content (46.8-52.1 g / L), water-soluble phosphorus content (49.7-58.6 g / L), and water-soluble potassium content (65.9-75.2 g / L) of the products in Examples 1-3 remained within suitable ranges, while the total amount of chelated trace elements reached 5.2-6.5 g / L, demonstrating the stability of this method in nutrient conversion.

[0085] Table 4 Comparison of pot experiment results (corresponding to Example 2 and Comparative Examples 1-3)

[0086] Group Plant height (cm) Stem diameter (cm) Fruit weight per plant (kg) Leaf SPAD value (relative chlorophyll content) Example 2 (Fertilizer B) 42.5 1.07 1.84 52.6 Comparative Example 1 (Fertilizer D) 32.8 0.85 1.32 43.1 Comparative Example 2 (Fertilizer E) 36.2 0.91 1.45 46.8 Comparative Example 3 (Fertilizer F) 39.1 0.98 1.58 49.5

[0087] The pot experiment data in Table 4 show that after applying the organic water-soluble fertilizer (fertilizer B) prepared in Example 2 of this invention, the tomato plants showed relatively good results in agronomic traits such as plant height, stem diameter, fruit yield per plant, and leaf SPAD value.

[0088] Compared to the comparative examples, Comparative Example 1 (Fertilizer D), lacking a nano-confined carrier, performed relatively weaker across various indicators. Comparative Example 2 (Fertilizer E), using a common carrier, showed improved performance, but still lagged behind the product of this invention. Comparative Example 3 (Fertilizer F), prepared by exogenously adding EDTA, also exhibited good results, but still showed a certain gap in single-plant fruit weight compared to the product of this invention.

[0089] In summary, this invention achieves the structurally controllable synthesis of organic water-soluble fertilizers at the nanoscale by integrating a three-pronged technical approach: nanoscale confined carrier construction, in-situ biomembrane catalysis, and template-induced self-chelation reconstruction. This method significantly improves the chelation efficiency of the product (chelated zinc and phosphorus ratios reach 82.5%–87.1% and 68.7%–74.2%, respectively), enhances the slow-release performance of nutrients (nitrogen and phosphorus leaching rates reduced to 13.8%–17.0% and 9.3%–11.5% after 30 days), and ultimately translates into excellent agricultural application results (tomato fruit weight reaches 1.84 kg per plant). This method enables the in-situ transformation and fixation of nutrients in organic waste, providing a technical pathway for developing organic water-soluble fertilizers with slow-release properties.

Claims

1. A method for preparing an anaerobic self-chelating organic water-soluble fertilizer, characterized in that, Includes the following steps: (a) Raw material pretreatment: crush livestock and poultry manure, crop straw or food processing by-products to a maximum particle size of no more than 1.0 mm, and adjust the material moisture content to 83%–87% and the carbon-nitrogen ratio to 18:1–22:1; (b) Carrier blending and biofilm construction: The material obtained in step (a) is uniformly mixed with a nano-confined carrier at a dry weight ratio of 5%–15%, wherein the nano-confined carrier is a porous material with a pore size of 20–80 nm and surface functional groups; the mixture is then placed in an anaerobic reactor and cultured for 3–7 days at a temperature of 30–40 °C, pH 6.5–7.5 and redox potential below -300 mV to form a stable biofilm; (c) Anaerobic mineralization and self-chelation reconstruction: Maintain an anaerobic environment, control the system temperature at 35–45℃ and the pH at 6.8–7.2 to carry out the mineralization reaction; monitor the concentration of short-chain fatty acids in the reaction system using an online near-infrared spectrometer, and when the total amount reaches 2000–3000 mg / L, automatically trigger the carrier-guided in-situ self-chelation reconstruction program, adjust the system pH to 6.0–7.0, and raise the temperature to 40–55℃, so as to promote the directional chelation and self-assembly of endogenous microbial metabolites and mineralized nutrient ions in the functional group guidance and nano-confined space of the nano-confined carrier, with a total reaction time of 15–25 days; (d) Post-processing of the product: The reaction liquid obtained in step (c) is subjected to solid-liquid separation, the liquid phase is collected and sterilized and concentrated to obtain the organic water-soluble fertilizer rich in organic-inorganic composite nanoparticles.

2. The method according to claim 1, characterized in that, The nano-confined carrier is selected from modified biochar, amino-modified mesoporous silica, and carboxyl-functionalized polymer composite porous materials.

3. The method according to claim 2, characterized in that, The nano-confined carrier is modified biochar, which is prepared by anaerobic carbonization of rice husks at 600℃, followed by impregnation in a phosphoric acid solution at a mass ratio of 1:2 for 24 hours, activation at 500℃, washing, and drying. Its pore size is 20–50 nm, and its specific surface area is 520–680 m². 2 / g, with a surface carboxyl group density of 0.9–1.3 mmol / g.

4. The method according to claim 2, characterized in that, The nano-confined support is amino-modified mesoporous silica, which is prepared by hydrolysis and condensation of tetraethyl orthosilicate as the silicon source and CTAB as the template in an ammonia solution at pH 11. After aging, washing, and calcination at 550°C, a mesoporous silica matrix is ​​obtained. This matrix is ​​then reacted with a 5 wt% solution of 3-aminopropyltriethoxysilane in toluene under reflux at 80°C. After washing and drying, the final product has an amino density of 0.8–1.1 mmol / g and a pore volume of 1.2–1.6 cm³. 3 / g.

5. The method according to claim 2, characterized in that, The nano-confined carrier is a carboxyl-functionalized polymer composite porous material, which is prepared by blending polyvinyl alcohol and sodium alginate in a mass ratio of 3:1, followed by freeze molding, glutaraldehyde crosslinking, and succinic anhydride carboxylation modification. Its pore size is 30–80 nm and its carboxyl density is 1.2–1.6 mmol / g.

6. The method according to claim 1, characterized in that, In step (b), during the biofilm construction stage, trace element solutions are continuously added to the system to achieve the following final concentrations: Ni 2 ⁺ 0.05–0.15 mg / L, Co 2 ⁺ 0.03–0.07 mg / L, Fe 2 ⁺ 0.1–0.3 mg / L.

7. An organic water-soluble fertilizer, characterized in that, It is prepared by the method described in any one of claims 1-6; the water-soluble fertilizer contains organic-inorganic composite nanoparticles, the average particle size of the nanoparticles is 80–150 nm, and the polydispersity index (PDI) is ≤0.19; and, by mass concentration, the proportion of chelated zinc in the water-soluble fertilizer is ≥82% of the total zinc, and the proportion of chelated phosphorus in the total water-soluble phosphorus is ≥68%.

8. The organic water-soluble fertilizer according to claim 7, characterized in that, The total nitrogen content is 35–55 g / L, the water-soluble phosphorus content is 40–60 g / L, the water-soluble potassium content is 50–80 g / L, and the total amount of chelated trace elements is not less than 5 g / L.