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

Abstract

The application discloses a kind of preparation methods of anaerobic self-chelation organic water-soluble fertilizer, belong to agricultural organic water-soluble fertilizer preparation technical field.The method includes: after being crushed and conditioned, organic waste is mixed with nano limited carrier with specific pore size and surface functional group, and biological membrane is constructed in anaerobic reactor;Subsequently, mineralization reaction is carried out, and self-chelation reconstruction program is automatically triggered by online monitoring short-chain fatty acid concentration, and endogenous metabolites and nutrient ions are directionally chelated and self-assembled in nano limited space under the guidance of carrier;Finally, after separation, sterilization and concentration, the finished product is obtained.The application prepares organic-inorganic composite nano fertilizer with average particle size of 80-150nm, chelated zinc ratio of ≥82% and chelated phosphorus ratio of ≥68% without relying on exogenous chelating agent, and the 30-day nitrogen and phosphorus leaching loss rate is less than 17.0% and 11.5%, which has good slow-release performance and agricultural yield-increasing effect, and provides a new technical approach for high-value resource utilization of organic waste.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of preparation of agricultural organic water-soluble fertilizer, and in particular relates to a preparation method of an anaerobic self-chelating organic water-soluble fertilizer. BACKGROUND

[0002] Under the framework of modern agricultural sustainable development, efficient resource utilization of organic waste is the key to building an ecological recycling and efficient fertilization system. Livestock manure, straw and food processing by-products and other wastes are rich in nitrogen, phosphorus, potassium and various trace elements, but their nutrients are mostly present in complex organic macromolecules, which degrade slowly and have low bioavailability. Although traditional composting technology can achieve partial stabilization, it still has problems such as long cycle, uncoordinated nutrient release, and easy loss, which makes it difficult to meet the comprehensive needs of precision agriculture for fertilizer quick-acting, slow-release and environmental protection.

[0003] Anaerobic biological conversion technology has become the mainstream treatment method because it can simultaneously achieve organic matter degradation, nitrogen stabilization and energy recovery. In order to further improve the effectiveness of phosphorus, potassium and trace elements, the industry has tried to add exogenous chelating agents (such as EDTA, humic acid salt or synthetic polymers). However, this strategy still has significant bottlenecks in industrial application: the introduction of exogenous chelating agents not only increases cost and process complexity, but also poses ecological toxicity and residual risks for certain compounds (such as EDTA), which violates the concept of green development; in addition, chelation reactions are mostly independent of the previous mineralization process, and the efficiency is significantly limited by ion concentration and diffusion, making it difficult to achieve efficient and targeted chelation assembly. Even if natural chelating agents are produced by lactic acid fermentation as described in Japanese patent JP2008023523A, it is still a non-targeted side reaction, lacks effective control over the morphology, structure and stability of the product, and cannot meet the requirements of high-end water-soluble fertilizer in terms of chelation efficiency, slow-release performance and nanometer uniformity.

[0004] In essence, the existing technology has a fundamental contradiction between "process fragmentation" and "structure disorder": microbial mineralization seeks widespread degradation of organic matter and ion release, and the reaction is random and dispersed; while efficient chelation requires ordered assembly and fixation of molecules and ions in a local microenvironment. There is an inherent conflict between thermodynamics and spatial organization. The lack of a mediation mechanism for synergistically regulating biological reactions and self-assembly at the nanoscale makes it difficult to balance high mineralization rate and high chelation rate, high ion concentration and high structural stability.

[0005] Therefore, the current core technical problem is: how to not rely on exogenous chelating agents and engineered strains, and through material design and microenvironment regulation, to construct a nanometer limited system with both biological catalysis enhancement and molecular template induction function in situ in an anaerobic reactor, to realize the spatiotemporal coupling and structure guidance of microbial mineralization and molecular self-assembly, and finally form an organic-inorganic composite with regular nanomorphology, narrow particle size distribution, high chelation efficiency and excellent slow-release performance. SUMMARY

[0006] To achieve the above-mentioned object, the present application adopts the following technical solutions:

[0007] The present application provides a preparation method of anaerobic self-chelating organic water-soluble fertilizer, comprising the following steps:

[0008] (a) raw material pretreatment: the livestock and poultry manure, crop straw or food processing by-products are crushed to a maximum particle size of not more than 1.0 mm, and the moisture content of the material is adjusted to 83%-87% and the carbon-nitrogen ratio is adjusted to 18:1-22:1;

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

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

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

[0012] Further, the nano-confined carrier is selected from modified biological carbon, amino-modified mesoporous silica, and carboxyl-functionalized high polymer composite porous material.

[0013] Further, the nano-confined carrier is modified biological carbon, which is prepared by immersing rice husk in a phosphoric acid solution at a mass ratio of 1:2 for 24 hours after anaerobic carbonization at 600°C, then washing and drying after activation at 500°C, and has a pore size of 20-50 nm, a specific surface area of 520-680 m 2 / g, and a surface carboxyl density of 0.9-1.3 mmol / g.

[0014] Further, the nano-limited carrier is amino-modified mesoporous silica, which is prepared by hydrolysis and condensation of tetraethyl orthosilicate as a silicon source and CTAB as a template in an ammonia solution with pH=11, followed by aging, washing, calcination at 550°C to obtain a mesoporous silica substrate, and then reflux reaction with 5wt% 3-aminopropyl triethoxysilane toluene solution at 80°C, and washing and drying to obtain the mesoporous silica with a surface amino density of 0.8-1.1mmol / g and a pore volume of 1.2-1.6cm 3 / g.

[0015] Further, the nano-limited carrier is carboxyl-functionalized high polymer composite porous material, which is prepared by blending polyvinyl alcohol and sodium alginate at a mass ratio of 3:1, followed by freeze forming, glutaraldehyde crosslinking, and succinic anhydride carboxyl modification to obtain the porous material with a pore size of 30-80nm and a carboxyl density of 1.2-1.6mmol / g.

[0016] Further, in the biological membrane construction stage of step (b), trace element solutions are continuously supplemented into the system to make the final concentrations of Ni 2 ⁺ 0.05-0.15mg / L, Co 2 ⁺ 0.03-0.07mg / L, and Fe 2 ⁺ 0.1-0.3mg / L.

[0017] The application also provides an organic water-soluble fertilizer prepared by the method, wherein the water-soluble fertilizer contains organic-inorganic composite nanoparticles with an average particle size of 80-150nm and a polydispersity index (PDI) of ≤0.19, and the proportion of chelated zinc in the total zinc and the proportion of chelated phosphorus in the total water-soluble phosphorus in the water-soluble fertilizer are ≥82% and ≥68%, respectively.

[0018] Further, the organic water-soluble fertilizer contains total nitrogen of 35-55g / L, water-soluble phosphorus of 40-60g / L, water-soluble potassium of 50-80g / L, and total chelated trace elements of not less than 5g / L.

[0019] Beneficial effects:

[0020] (1) The application successfully realizes in-situ efficient chelation of nutrients by guiding endogenous microbial metabolites and mineralized nutrient ions to directionally self-assemble in a limited space through a nano-limited carrier. The examples show that the proportions of chelated zinc and chelated phosphorus in the final product are 82.5%-87.1% and 68.7%-74.2%, respectively, without the need for adding external chelating agents such as EDTA, which avoids chemical residues and potential ecological risks from the source, and meets the development requirements of green agriculture.

[0021] (2) The present application couples the two traditionally split processes of microbial mineralization and molecular self-chelation. By monitoring the concentration of short-chain fatty acids online as a trigger signal, the reconstruction program is intelligently started, so that the release and fixation of nutrients are synchronized, solving the technical contradiction of high mineralization rate and high chelation rate, and improving the process efficiency and controllability.

[0022] (3) Under the synergistic effect of carrier functional groups and nano-limited space, the final product forms a structured organic-inorganic composite nanoparticle with an average particle size of 80-150 nm and a uniform distribution (PDI≤0.19). This nanostructure gives the product good slow-release performance, with 30-day nitrogen and phosphorus cumulative loss rates as low as 13.8%-17.0% and 9.3%-11.5%, respectively, significantly higher than traditional process products, effectively reducing nutrient loss and improving utilization efficiency.

[0023] (4) The product of the present application not only has high chelated trace element content, but also has total nitrogen (35-55 g / L), water-soluble phosphorus (40-60 g / L), and water-soluble potassium (50-80 g / L) content reaching the standard of commercial water-soluble fertilizer, integrating quick-acting nutrients and slow-release micro-fertilizer, and meeting the nutrient needs of crops throughout the growth period. Pot experiment confirmed that the application of the product can significantly promote tomato growth and improve yield and quality.

[0024] (5) The present application converts livestock manure, straw and other organic waste into high-value nano-structured water-soluble fertilizer, with a green and efficient process route, not only solving the problem of waste disposal, but also turning waste into treasure, creating economic value, and providing strong technical support for sustainable agricultural development. DETAILED DESCRIPTION

[0025] In order to enable personnel in the technical field to better understand the technical solutions in the present application, the following will further describe the present application in detail in combination with embodiments.

[0026] Example 1: Using modified biochar as carrier

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

[0028] 2. Preparation of modified biochar: rice husk as precursor, carbonized under anaerobic atmosphere at 600 °C for 2 hours with a heating rate of 5 °C / min. The carbonized product was mixed with 85% phosphoric acid at a mass ratio of 1:2 for impregnation for 24 hours, followed by activation at 500 °C for 1 hour (heating rate of 10 °C / min), repeatedly washed with deionized water until the pH of the washing liquid was neutral, and dried at 80 °C for 12 hours, to obtain modified biochar with a pore size of 30 nm (determined by BET (Brunauer-Emmett-Teller) adsorption instrument), a specific surface area of 660 m 2 / g (determined by BET adsorption instrument), and a surface carboxyl group density of 1.15 mmol / g (determined by Fourier transform infrared spectrometer).

[0029] 3. Carrier blending and biofilm construction: the pretreated material obtained in step 1 above was mixed with 5 kg (dry weight, accounting for 5% of the dry weight of the pretreated material) of the modified biochar carrier prepared in step 2 into a double-shaft mixer, mixed at 30 rpm for 25 minutes until uniformly dispersed. The mixture was transferred into a 50 L anaerobic reactor, maintained at a temperature of 40 °C, a pH of 7.5, an oxidation-reduction potential (ORP) of -320 mV, and cultured for 7 days to form a stable biofilm. During the period, trace element solution was continuously supplemented to maintain the concentrations of Ni 2 ⁺, Co 2 ⁺, and Fe 2 ⁺ in the system 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 was performed: the anaerobic environment was maintained, the temperature was adjusted to 35 °C, the pH was adjusted to 7.2, and the mineralization reaction was performed. Then, the self-chelation reconstruction program was started: the concentration of short-chain fatty acids in the reaction system was monitored by an online near-infrared spectrometer. When the total amount reached 2000 mg / L (on the 10th day), the reconstruction program was triggered: the pH was automatically adjusted to 7.0, the temperature was raised to 40 °C, the stirring speed was adjusted to 30 rpm, and the reaction was continued until the total period was 25 days.

[0031] 5. Product post-treatment: after the reaction was completed, solid-liquid separation was performed by a horizontal screw centrifuge (2500 rpm, 12 min) to obtain a crude liquid phase, which was then subjected to cross-flow filtration through a 0.2 μm ceramic membrane (transmembrane pressure (TMP) 0.15 MPa). The filtrate was subjected to instantaneous sterilization at 125 °C for 10 s, and then concentrated at 50 °C and -0.09 MPa to a total nutrient concentration of 205 g / L to obtain the finished product organic water-soluble fertilizer A.

[0032] Example 2: Amino-modified mesoporous silica as carrier

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

[0034] 2. Preparation of amino-modified mesoporous silica: Using tetraethyl orthosilicate (TEOS) as the silicon source and cetyltrimethylammonium bromide (CTAB) as the template, hydrolysis and condensation were carried out in an ammonia solution at pH = 11, with a mass ratio of TEOS:CTAB:water of 1:0.3:10. After aging for 24 hours, washing with deionized water until no CTAB residue was left, and calcining at 550°C for 4 hours, a mesoporous silica matrix was obtained. Then, a 5% 3-aminopropyltriethoxysilane toluene solution (10 times the mass of the mesoporous silica matrix) was added and refluxed at 80°C for 6 hours. After washing with anhydrous ethanol three times and drying at 60°C for 12 hours, a product with a surface amino density of 0.95 mmol / g (determined by Fourier transform infrared spectroscopy) and a pore volume of 1.4 cm 3 / g (determined by BET adsorption) was obtained.

[0035] 3. Carrier blending and biofilm construction: The pretreated material obtained in step 1 above was mixed with 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 in a double-shaft mixer at 30 rpm for 25 minutes until evenly dispersed. The mixture was transferred to a 50L anaerobic reactor, maintained at a temperature of 35°C, pH 7.0, and ORP -350mV, and cultured for 5 days to form a stable biofilm. During this period, trace element solution was continuously supplemented to maintain the concentrations of Ni 2 ⁺, Co 2 ⁺, and Fe 2 ⁺ 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: maintain an anaerobic environment, adjust the temperature to 40°C, and the pH to 7.0, and carry out the mineralization reaction. Then, start the self-chelation reconstruction program: when the online near-infrared spectrometer detects that the total amount of short-chain fatty acids reaches 2500 mg / L (on the 8th day), automatically trigger the carrier-guided in-situ self-chelation reconstruction program: automatically adjust the pH to 6.5, increase the temperature to 47°C, and adjust the stirring speed to 30 rpm, and continue the reaction until the total period is 20 days.

[0037] 5. Product post-treatment: As in Example 1, after concentration, the finished organic water-soluble fertilizer B is obtained, with a total nutrient concentration of 215 g / L.

[0038] Example 3: Carboxyl-functionalized polymer composite porous material as carrier

[0039] 1. Raw material pretreatment: 100 kg (dry weight) of bean dregs and mushroom dregs (mass ratio 1:1) were crushed to a maximum particle size of ≤1.0 mm. The moisture content was adjusted 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 blended at a mass ratio of 3:1 to prepare a 10% aqueous solution. Sodium bicarbonate was added as a porogen at a concentration of 5% of the total mass of the aqueous solution. The composite porous material was obtained by freezing at -20°C for 12 hours, replacing with tert-butyl alcohol (5 times the volume of the frozen material) for 24 hours, and freeze-drying for 48 hours. Then, the material was cross-linked 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, and carboxylated with a 5% succinic anhydride dimethylformamide (DMF) solution (15 times the mass of the cross-linked material) at 60°C for 3 hours. Finally, the material was washed repeatedly with deionized water until no residual reagents were present, and dried at 40°C for 24 hours. The resulting porous material had a pore size of 60 nm (determined using a BET adsorption instrument) and a carboxyl group density of 1.3 mmol / g (determined using a Fourier transform infrared spectrometer).

[0041] 3. Carrier blending and biofilm construction: The pretreated material obtained in step 1 was mixed with 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 in a double-shaft mixer at 30 rpm for 25 minutes until evenly dispersed. The mixture was transferred to a 50L anaerobic reactor and maintained at a temperature of 30°C, pH 6.5, and ORP-380mV for 3 days to form a stable biofilm. During this period, trace element solution was continuously added to maintain the concentrations of Ni 2 ⁺, Co 2 ⁺, and Fe 2 ⁺ 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 was performed: the anaerobic environment was maintained, the temperature was adjusted to 45°C, and the pH was adjusted to 6.8 for mineralization. Then, the self-chelation reconstruction program was started: when the total amount of short-chain fatty acids reached 3000 mg / L (on the 5th day) as monitored by an online near-infrared spectrometer, the carrier-guided in-situ self-chelation reconstruction program was automatically triggered: the pH was automatically adjusted to 6.0, the temperature was increased to 55°C, the stirring speed was adjusted to 30 rpm, and the reaction continued for a total period of 15 days.

[0043] 5. Product post-treatment: same as Example 1, after concentration, the product organic water-soluble fertilizer C is obtained, with total nutrient concentration of 198 g / L.

[0044] Comparative Example 1: without nano-confined carrier (including the nano-confined carrier defined in the present application, such as modified biochar, amino-modified mesoporous silica, or carboxyl-functionalized polymer composite porous material)

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

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

[0047] The preparation steps of this comparative example are completely the same as Example 1, the only difference is that an equal amount of commercial unmodified activated carbon (specific surface area 550 m 2 / g, but the surface functional groups are few, and the carboxyl density is <0.2 mmol / g) is used instead of the modified biochar carrier. Finally, liquid fertilizer E is obtained.

[0048] Comparative Example 3: exogenous addition of EDTA chelating agent

[0049] The preparation steps of this comparative example are completely the same as the first half of Example 2 (including the use of amino-modified mesoporous silica carrier and the anaerobic mineralization process). The difference is that after the mineralization reaction is completed, the self-chelation reconstruction program is not started, but instead, ethylenediaminetetraacetic acid disodium salt (EDTA disodium salt) is directly added to the reaction system, so that the total molar ratio of EDTA disodium salt to all metal ions (mainly Zn 2 ⁺, Fe 2 ⁺, Mn 2 ⁺, Cu 2 ⁺) that can be chelated in the system is 1.2:1, and the chelation is carried out by stirring for 2 hours, and then subsequent post-treatment is carried out. Finally, liquid fertilizer F is obtained.

[0050] Effect experiment and data analysis

[0051] 1. Biocompatibility test (toxicity evaluation) of nano-confined carrier

[0052] The MTT (3-(4,5-dimethylthiazole-2)-2,5-diphenyl tetrazolium bromide) method was used to determine the effect of carrier materials on the activity of anaerobic microorganisms. After co-culturing the carrier extract and the enriched endogenous anaerobic microorganisms for 4 hours, the relative survival rate and inhibition rate of the cells were detected.

[0053] 2. Microbial adhesion test on nano-confined carriers (evaluation of enrichment capacity)

[0054] The adhesion capacity of microorganisms on the surface of the carrier was quantified by plate counting method. After co-culturing the sterilized carrier material with the microbial suspension (1 x 10 7 CFU / mL) under anaerobic conditions for 24 hours, the adhesion amount of microorganisms on the surface of the carrier was counted by ultrasonic stripping and plate counting.

[0055] 3. Product performance determination and agricultural effect verification of the organic water-soluble fertilizers A, B and C prepared in Examples 1-3 of the present application and the organic water-soluble fertilizers D, E and F prepared in Comparative Examples 1-3.

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

[0057] The sample was diluted to an appropriate concentration and placed in a special sample cell. Dynamic light scattering instrument (DLS) was used. After the nanoparticles were irradiated with a helium-neon laser with a wavelength of 633 nm, the scattering of the nanoparticles occurred. The fluctuation rate of the scattering light intensity was analyzed by a detector. The hydrodynamic particle size distribution and PDI (polydispersity index) value were calculated using the Stokes-Einstein equation, which characterized the width of the particle size distribution.

[0058] (2) Chelated zinc proportion / chelated phosphorus proportion

[0059] A certain amount of sample was taken and high-speed centrifugation was performed using an ultrafiltration centrifuge tube with a molecular weight cut-off of 3 kDa. Free ions can pass through the ultrafiltration membrane into the filtrate, while chelated macromolecular complexes are trapped in the concentrate. The filtrate and the retentate were collected respectively. The elemental concentration of zinc or phosphorus in the two parts was accurately determined by inductively coupled plasma optical emission spectrometer (ICP-OES). The chelation rate was calculated by the proportion in the retentate.

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

[0061] The soil dried by quantitative air and passed through a 2mm sieve was filled in a PVC leaching column with an inner diameter of 5cm and a height of 30cm according to the standard bulk density (1.2 g / cm 3 ). The test fertilizer containing equal amounts of nitrogen (1.0g) and phosphorus (0.5g) was mixed with the surface 5cm soil. Deionized water was added quantitatively (20mL) every day to simulate rainfall. The daily leachate was collected and measured. After 30 days of leaching, the total amount of specific nutrient ions (NH4⁺, NO3⁻, PO4 3 ⁻) in all leachates was determined by ion chromatography (IC) or molybdenum antimony spectrophotometry (for phosphorus), and the percentage relative to the total amount of nutrients added was calculated, which was the cumulative leaching rate.

[0062] (4) Total nitrogen content

[0063] The sample was digested in concentrated sulfuric acid, and organic nitrogen and ammonium nitrogen were converted into ammonium sulfate. After alkalization, ammonia was distilled out, 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 the sample was extracted with water, orthophosphate reacted with molybdate and metavanadate under acidic conditions to form a yellow vanadium-molybdenum phosphate complex. The absorbance was measured at a wavelength of 420 nm, and quantified by a standard curve.

[0066] (6) Water-soluble potassium content

[0067] After the sample solution was atomized and sprayed into a high-temperature flame, the potassium element was excited to emit characteristic light at a wavelength of 766.5 nm, and the intensity was proportional to the potassium content. The intensity was detected for quantification.

[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. The sample was directly injected after appropriate dilution or acid digestion. The elements were atomized and excited by inductively coupled plasma (ICP) at high temperature, and the emission intensity at each characteristic wavelength of the trace elements was detected for simultaneous quantification.

[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] Tomato (variety: 'Jinfen No. 1') was used as the test crop for pot experiment, with 10 replicates (n = 10, where n represents the number of biological replicates) for each treatment. The growth period was 60 days. The biological characteristics 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 material 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 are all less than 4%, confirming that they have no significant toxic effect on microbial growth.

[0076] Table 2: Microbial adhesion amount test results of the carriers used in Examples 1-3

[0077] Carrier type Microbial attachment (CFU / cm 2 ) Modified biochar (6.8 ± 0.5) x 10 7 ]] Amino-modified mesoporous silica (5.2 ± 0.4) x 10 7 ]] Carboxyl-functionalized polymer composite porous material (7.1 ± 0.6) x 10 7 ]] Blank control (smooth surface) (3.2 ± 0.3) x 10 5 ]]

[0078] The data in Table 2 show that the adhesion amounts of the three carriers all reach 107 CFU / cm 2 The magnitude is significantly higher than the blank control, proving that the porous structure and surface functional groups can effectively promote microbial adhesion.

[0079] Table 3 Comparison table of product performance indicators (corresponding to examples 1-3 and comparative examples 1-3)

[0080] Detection index 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 Chelated Zn proportion (%) 82.5 85.3 87.1 15.2 35.8 92.5 Chelated P proportion (%) 68.7 71.5 74.2 8.5 22.1 70.8 N leaching rate in 30 days (%) 17.0 15.1 13.8 48.5 36.2 25.7 P leaching rate in 30 days (%) 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 can be seen from Table 3, the average particle size of the products prepared in examples 1-3 is in the range of 82-148 nm, and the polydispersity index (PDI value) is less than 0.19, indicating that uniform nanoparticles can be formed by this method. In contrast, the product of comparative example 1 lacks a nano-confined carrier and appears macro-flocculation, while the product of comparative example 2 using a common carrier has a relatively wide particle size distribution.

[0082] The proportion of chelated zinc in the products of examples 1-3 reaches 82.5%-87.1%, and the proportion of chelated phosphorus reaches 68.7%-74.2%, showing that this method can achieve effective nutrient fixation without relying on exogenous chelating agents. Although comparative example 3 achieves a high zinc chelation rate (92.5%) by adding EDTA, its phosphorus chelation rate (70.8%) is relatively limited, and this method introduces an exogenous chemical chelating agent (EDTA), which has ecological toxicity risks and does not meet the requirements of green agriculture.

[0083] In the 30-day leaching test, the nitrogen leaching rate of the products of examples 1-3 is 13.8%-17.0%, and the phosphorus leaching rate is 9.3%-11.5%, which is lower than that of each comparative example. This shows that the fertilizer product obtained by this method has 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 of examples 1-3 are all maintained within the appropriate range, while the total amount of chelated trace elements reaches 5.2-6.5 g / L, showing the stability of this method in nutrient transformation.

[0085] Table 4 Comparison table 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 the present application, the tomato plants showed relatively good effects in terms of plant height, stem diameter, single plant fruit yield, and leaf SPAD value, among other agronomic trait indicators.

[0088] Compared with the comparative examples, the comparative example 1 (fertilizer D) lacking nano-confined carriers performed relatively weak in various indicators. The comparative example 2 (fertilizer E) using ordinary carriers had improved effect, but was still lower than the product of the present application. The comparative example 3 (fertilizer F) prepared by exogenous addition of EDTA also showed good effect, but still had certain gap with the product of the present application in single fruit weight.

[0089] In summary, the present application realizes the controllable synthesis of organic water-soluble fertilizer in nanoscale through the trinity technical path of fusion nano-confined carrier construction, in-situ catalysis of biological membrane and template-induced self-chelation reconstruction. The method significantly improves the chelation efficiency of the product (chelated zinc and phosphorus account for 82.5%-87.1% and 68.7%-74.2%, respectively), enhances the slow-release performance of nutrients (the 30-day leaching rates of nitrogen and phosphorus are reduced to 13.8%-17.0% and 9.3%-11.5%, respectively), and finally converts into good agricultural application effect (the single fruit weight of tomato reaches 1.84 kg). The method realizes the in-situ conversion and fixation of nutrients in organic waste, and provides a technical path for the development of organic water-soluble fertilizer with slow-release characteristics.

Claims

1. A method for preparing an anaerobic self-chelating organic water-soluble fertilizer, characterized by, The method comprises the following steps: (a) raw material pretreatment: livestock and poultry manure, crop straw or food processing by-products are crushed to a maximum particle size of not more than 1.0 mm, and the moisture content of the material is adjusted to 83%-87% and the carbon-nitrogen ratio is adjusted to 18:1-22:1; (b) carrier mixing and biofilm construction: the material obtained in step (a) is uniformly mixed with nano-limited carriers selected from one of modified biochar, amino-modified mesoporous silica and carboxyl-functionalized polymer composite porous material at a dry weight mass ratio of 5%-15%; then the mixture is placed in an anaerobic reactor and cultured at a temperature of 30-40°C, a pH of 6.5-7.5 and an oxidation-reduction potential of less than -300 mV for 3-7 days to form a stable biofilm; wherein the modified biochar is prepared by immersing rice husk in a phosphoric acid solution at a mass ratio of 1:2 for 24 hours after anaerobic carbonization at 600°C, followed by washing and drying after activation at 500°C, and has a pore size of 20-50 nm, a specific surface area of 520-680 m² / g and a surface carboxyl density of 0.9-1.3 mmol / g; the amino-modified mesoporous silica is obtained by hydrolysis and condensation in an ammonia solution at pH=11 using tetraethyl orthosilicate as a silicon source and CTAB as a template, followed by aging, washing, calcination at 550°C to obtain a mesoporous silica substrate, and then refluxing with 5wt% 3-aminopropyltriethoxysilane toluene solution at 80°C, followed by washing and drying, and has a surface amino density of 0.8-1.1 mmol / g and a pore volume of 1.2-1.6 cm³ / g; the carboxyl-functionalized polymer composite porous material is prepared by blending polyvinyl alcohol and sodium alginate at a mass ratio of 3:1, followed by freeze forming, glutaraldehyde crosslinking and succinic anhydride carboxylation modification, and has a pore size of 30-80 nm and a carboxyl density of 1.2-1.6 mmol / g; (c) anaerobic mineralization and self-chelation reconstruction: the system temperature is controlled at 35-45°C and the pH is controlled at 6.8-7.2 to carry out the mineralization reaction; the concentration of short-chain fatty acids in the reaction system is monitored by an online near-infrared spectrometer, and when the total amount reaches 2000-3000 mg / L, the carrier-guided in-situ self-chelation reconstruction program is automatically triggered, the pH of the system is adjusted to 6.0-7.0, and the temperature is raised to 40-55°C to promote the directional chelation and self-assembly of endogenous microbial metabolites and nutrient ions released by mineralization in the functional group guidance and nano-limited space of the nano-limited carrier, and the total reaction time is 15-25 days; (d) product post-treatment: 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 of claim 1, wherein, In step (b), trace element solutions are continuously supplemented to the system during the biofilm construction stage to make the final concentrations of Ni²⁺, Co²⁺ and Fe²⁺ 0.05-0.15 mg / L, 0.03-0.07 mg / L and 0.1-0.3 mg / L, respectively.

3. An organic water-soluble fertilizer, characterized by, It is prepared by the method of any one of claims 1-2; the water-soluble fertilizer contains organic-inorganic composite nanoparticles, the average particle size of the nanoparticles is 80-150 nm, the polydispersity index (PDI) is ≤0.19; and the proportion of chelated zinc in the total zinc in the water-soluble fertilizer is ≥82% and the proportion of chelated phosphorus in the total water-soluble phosphorus is ≥68% in terms of mass concentration.

4. The organic water soluble fertilizer according to claim 3, 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 in terms of mass concentration.