Method for producing plant nutrient solution by subcritical hydrolysis coupled nano-catalytic degradation of agricultural byproduct organic materials

Abstract

The invention discloses a method for producing a plant nutrient solution by subcritical hydrolysis coupled nano-catalytic degradation of agricultural by-product organic materials. The method comprises the following steps: S1, crushing the agricultural by-product organic materials; s2, adding a composite nano catalyst; s3, placing the mixture in a subcritical hydrolysis reaction kettle to complete a subcritical hydrolysis reaction; s4, adding nano humic acid and a compound microbial agent; s5, standing at 25 to 35 DEG C for 3 to 7 days; and S6, carrying out solid-liquid separation. The method has the advantages that 1) the hydrolysis efficiency of the organic materials is improved by 40-60% by combining a subcritical hydrolysis technology with nano-catalysis, and the treatment period is shortened to be within 7 days; 2) through the synergistic effect of nanometer material catalysis and microbial degradation, the removal rate of pesticide residues and pathogenic bacteria is significantly improved, and the fixation rate of heavy metal lattices can reach more than or equal to 99%, and 3) the content of water-soluble organic matters in the plant nutrient solution is more than or equal to 30%, the total nutrient (N + P2O5 + K2O) of nitrogen phosphorus and potassium is more than or equal to 8%, and the plant absorption efficiency is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of agricultural by-product organic materials resource utilization technology, and in particular to a method for resource utilization treatment of agricultural by-product organic materials using subcritical hydrolysis. Background Technology

[0002] With the development of intensive agriculture, the improper disposal of large quantities of organic agricultural by-products and organic materials such as livestock and poultry manure, crop straw, and fruit and vegetable waste will lead to serious environmental pollution and resource waste. Although traditional composting and anaerobic fermentation technologies are widely used, they still have problems such as long processing cycles (usually 30 to 60 days), significant nutrient loss, and incomplete removal of pesticide residues and heavy metals.

[0003] Subcritical water treatment technology, as an emerging method for treating organic waste, can maintain water in a liquid state under high temperature and pressure (150–374℃), possessing extremely strong dissolving power and reactivity. It can rapidly hydrolyze large organic molecules such as cellulose and proteins, and has the potential to serve as a means of resource utilization for agricultural by-products. However, single subcritical technology has limited ability to degrade certain stubborn pollutants (such as organophosphorus pesticides and pyrethroid pesticides) and insufficient ability to regulate the speciation of heavy metals.

[0004] Nanomaterials are widely used in the degradation of environmental pollutants due to their high specific surface area, excellent catalytic activity, and photocatalytic performance. However, current technologies mostly use a single nanocatalyst, and there is a lack of research on combining them with subcritical technology systems for the conversion of organic materials and the deep removal of pesticide residues. In particular, there are no systematic reports on the synergistic catalytic research of composite nanocatalysts and their optimized application in practical organic waste treatment systems.

[0005] Therefore, developing an efficient, rapid, and harmless method for converting agricultural by-products into organic materials based on the synergistic effect of subcritical hydrolysis technology and composite nanocatalysts has significant practical implications and application prospects. Summary of the Invention

[0006] To improve the degradation rate of pesticide residues, nutrient utilization, and degradation efficiency of agricultural by-product organic materials, this invention provides a method for producing plant nutrient solution by degrading agricultural by-product organic materials through subcritical hydrolysis coupled with nanocatalysis.

[0007] The technical solution adopted in this invention is a method for producing plant nutrient solution by subcritical hydrolysis coupled with nanocatalysis to degrade agricultural by-product organic materials, comprising the following steps:

[0008] S1. Crush agricultural by-product organic materials to a particle size of 10-20cm to obtain pretreated materials;

[0009] S2. Add 0.5% to 2% of a composite nanocatalyst, comprising nano-titanium carbide, to the pretreated material to obtain a mixture;

[0010] S3. Place the mixture in a subcritical hydrolysis reactor to complete the subcritical hydrolysis reaction and obtain the hydrolysis product;

[0011] S4. Add 1% to 3% of nano-humic acid and 0.1% to 0.5% of composite microbial agent by mass of the hydrolysis product to the hydrolysis product, stir and mix evenly to obtain a mixture.

[0012] S5. Let the mixture stand at 25-35°C for 3-7 days to obtain a mixed slurry;

[0013] S6. The liquid phase obtained by solid-liquid separation and filtration of the mixed slurry is the plant nutrient solution.

[0014] As will be readily understood by those skilled in the art, the "agricultural by-product organic materials" mentioned in this invention refer to organic by-products generated from planting, breeding, animal husbandry, forestry, etc., such as straw, fruit peels, animal manure, fallen leaves and flowers of trees, etc.

[0015] As will be readily understood by those skilled in the art, the subcritical hydrolysis reactor in this invention can use known subcritical hydrolysis devices, such as the subcritical hydrolysis device disclosed in CN114700356A. The reactor can be made of stainless steel and uses a steam pressurization system to ensure precise and controllable pressure; it can also be equipped with an anti-winding chain feeding system, a safety pressure valve group, an automatic monitoring and control system, etc., to facilitate fully unmanned intelligent operation from feeding to discharging and improve safety.

[0016] As a further improvement of the present invention, the composite nanocatalyst is composed of nano-titanium carbide and nano-cerium dioxide in a mass ratio of 1:0.1 to 0.8. The preferred particle size range of the composite nanocatalyst is D50 = 15 to 80 nm.

[0017] More preferably, the subcritical hydrolysis reaction in step S3 has a reaction temperature of 374.2℃, a reaction pressure of 22.1MPa, and a reaction time of 40–120s.

[0018] As a further improvement of the present invention, the composite microbial agent includes Bacillus subtilis and yeast, with a total viable count ≥1×10⁻⁶. 8 CFU / g. The optimal ratio of viable Bacillus subtilis to yeast is 1.2–3:1.

[0019] As a further improvement of the present invention, the nano-humic acid particle size D50 is 10-220 nm. Those skilled in the art will understand that the nano-humic acid described in this invention is a humic acid material produced by further processing traditional humic acid through physical, chemical, or biological methods to achieve a nano-sized particle size, and is commercially available. It not only reduces particle size, but also significantly enhances its surface properties and reactivity.

[0020] Those skilled in the art will understand that, since the solid particles of the mixed slurry obtained in step S5 of the present invention are relatively fine, a suitable solid-liquid separation method should be selected in step S6 to ensure that too much solid phase is not mixed into the plant nutrient solution, affecting sales and use. For example, pressure filtration, membrane filtration, etc. can be used. Through experiments, we have provided a better solution, namely, the solid-liquid separation method in S6 is pressure filtration by a plate and frame filter press.

[0021] The present invention also discloses a plant nutrient solution, which is prepared by the method of the present invention for producing plant nutrient solution by subcritical hydrolysis coupled with nanocatalysis to degrade agricultural by-product organic materials.

[0022] The present invention also discloses a method for planting crops, characterized in that the planting method includes the step of applying the plant nutrient solution of the present invention.

[0023] The beneficial effects of this invention are: 1) This invention uses subcritical hydrolysis technology combined with nanocatalysis to increase the hydrolysis efficiency of organic materials by 40% to 60% and shorten the treatment cycle to within 7 days; 2) This invention significantly improves the removal rate of pesticide residues and pathogens through the synergistic effect of nanomaterial catalysis and microbial degradation, and the heavy metal lattice fixation rate can reach ≥99%; 3) The plant nutrient solution prepared by the method of this invention has a water-soluble organic matter content of ≥30% and a total nitrogen, phosphorus and potassium nutrient (N+P2O5+K2O) content of ≥8%, which significantly improves the plant absorption efficiency; 4) The method of this invention has no secondary pollution throughout the process, and the resource utilization rate of organic by-products is ≥95%, which meets the needs of green and sustainable agricultural development. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments.

[0025] Example 1:

[0026] Agricultural by-product organic materials should be processed using the following method:

[0027] (1) Agricultural by-product organic materials (composed of pig manure and corn stalks in a mass ratio of 1:3, wherein the pig manure is from the same batch and the corn stalks are from the same experimental field, and cypermethrin is applied evenly during the corn growth process) are crushed to a particle size of 10-20 cm to obtain pretreated materials;

[0028] (2) Add 1% by mass of nano-titanium carbide (D50=26nm) to the pretreated material to obtain a mixture;

[0029] (3) The mixture was placed in a subcritical hydrolysis reactor to complete the subcritical hydrolysis reaction at a reaction temperature of 374.2℃, a reaction pressure of 22.1MPa, and a reaction time of 60s to obtain the hydrolysis product;

[0030] (4) Add 2% by mass of nano-humic acid (D50=19nm) and 0.2% by mass of composite microbial agent to the hydrolysis product, stir and mix evenly to obtain a mixture; wherein the total viable count of the composite microbial agent is 1.8×10 8 CFU / g is composed of Bacillus subtilis and yeast in a live cell ratio of 2:1.

[0031] (5) The mixture is left to stand at 28°C for 7 days to obtain a mixed slurry;

[0032] (6) The mixed slurry is filtered by a plate and frame filter press, and the filtered liquid phase is the plant nutrient solution.

[0033] Example 2:

[0034] Agricultural by-product organic materials should be processed using the following method:

[0035] (1) Agricultural by-product organic materials (composed of pig manure and corn stalks in a mass ratio of 1:3, wherein the pig manure is from the same batch and the corn stalks are from the same experimental field, and cypermethrin is applied evenly during the corn growth process) are crushed to a particle size of 10-20 cm to obtain pretreated materials;

[0036] (2) Add 1.5% by mass of nano-titanium carbide (D50=43nm) to the pretreated material to obtain a mixture;

[0037] (3) The mixture was placed in a subcritical hydrolysis reactor to complete the subcritical hydrolysis reaction at a reaction temperature of 374.2℃, a reaction pressure of 22.1MPa, and a reaction time of 80s to obtain the hydrolysis product;

[0038] (4) Add 1% by mass of nano-humic acid (D50=19nm) and 0.13% by mass of composite microbial agent to the hydrolysis product, stir and mix evenly to obtain a mixture; wherein the total viable count of the composite microbial agent is 1.2×10 8 CFU / g is composed of Bacillus subtilis and yeast in a live cell ratio of 3:1.

[0039] (5) The mixture is left to stand at 28°C for 7 days to obtain a mixed slurry;

[0040] (6) The mixed slurry is filtered by a plate and frame filter press, and the filtered liquid phase is the plant nutrient solution.

[0041] Example 3:

[0042] Agricultural by-product organic materials should be processed using the following method:

[0043] (1) Agricultural by-product organic materials (composed of pig manure and corn stalks in a mass ratio of 1:3, wherein the pig manure is from the same batch and the corn stalks are from the same experimental field, and cypermethrin is applied evenly during the corn growth process) are crushed to a particle size of 10-20 cm to obtain pretreated materials;

[0044] (2) Add 0.5% by mass of nano-titanium carbide (D50=12nm) to the pretreated material to obtain a mixture;

[0045] (3) The mixture was placed in a subcritical hydrolysis reactor to complete the subcritical hydrolysis reaction at a reaction temperature of 374.2℃, a reaction pressure of 22.1MPa, and a reaction time of 45s to obtain the hydrolysis product;

[0046] (4) Add 3% by mass of nano-humic acid (D50=19nm) and 0.4% by mass of composite microbial agent to the hydrolysis product, stir and mix evenly to obtain a mixture; wherein the total viable count of the composite microbial agent is 3.6×10 8 CFU / g is composed of Bacillus subtilis and yeast in a live cell ratio of 1.5:1.

[0047] (5) The mixture is left to stand at 28°C for 7 days to obtain a mixed slurry;

[0048] (6) The mixed slurry is filtered by a plate and frame filter press, and the filtered liquid phase is the plant nutrient solution.

[0049] Example 4:

[0050] This example is a control experiment of Example 1, carried out according to the same steps and conditions as Example 1. The difference is that the nanocatalyst used is a mixture of nano-titanium carbide and nano-cerium dioxide in a mass ratio of 1:0.2, and the total amount of nanocatalyst used remains unchanged. The specific scheme is as follows:

[0051] (1) Agricultural by-product organic materials (composed of pig manure and corn stalks in a mass ratio of 1:3, wherein the pig manure is from the same batch and the corn stalks are from the same experimental field, and cypermethrin is applied evenly during the corn growth process) are crushed to a particle size of 10-20 cm to obtain pretreated materials;

[0052] (2) Add 1% of the mass of the pretreated material to the pretreated material to a composite nano-catalyst (composed of nano-titanium carbide and nano-cerium dioxide in a mass ratio of 1:0.2, D50=26nm), to obtain a mixture;

[0053] (3) The mixture was placed in a subcritical hydrolysis reactor to complete the subcritical hydrolysis reaction at a reaction temperature of 374.2℃, a reaction pressure of 22.1MPa, and a reaction time of 60s to obtain the hydrolysis product;

[0054] (4) Add 2% by mass of nano-humic acid (D50=19nm) and 0.2% by mass of composite microbial agent to the hydrolysis product, stir and mix evenly to obtain a mixture; wherein the total viable count of the composite microbial agent is 1.8×10 8 CFU / g is composed of Bacillus subtilis and yeast in a live cell ratio of 2:1.

[0055] (5) The mixture is left to stand at 28°C for 7 days to obtain a mixed slurry;

[0056] (6) The mixed slurry is filtered by a plate and frame filter press, and the filtered liquid phase is the plant nutrient solution.

[0057] Example 5:

[0058] This example is a control experiment of Example 1, carried out according to the same steps and conditions as Example 1, the difference being that: all the nanocatalysts used are nano-cerium dioxide, and the total amount of nanocatalyst used remains unchanged. The specific scheme is as follows:

[0059] (1) Agricultural by-product organic materials (composed of pig manure and corn stalks in a mass ratio of 1:3, wherein the pig manure is from the same batch and the corn stalks are from the same experimental field, and cypermethrin is applied evenly during the corn growth process) are crushed to a particle size of 10-20 cm to obtain pretreated materials;

[0060] (2) Add 1% by mass of nano-cerium dioxide (D50=26nm) to the pretreated material to obtain a mixture;

[0061] (3) The mixture was placed in a subcritical hydrolysis reactor to complete the subcritical hydrolysis reaction at a reaction temperature of 374.2℃, a reaction pressure of 22.1MPa, and a reaction time of 60s to obtain the hydrolysis product;

[0062] (4) Add 2% by mass of nano-humic acid (D50=19nm) and 0.2% by mass of composite microbial agent to the hydrolysis product, stir and mix evenly to obtain a mixture; wherein the total viable count of the composite microbial agent is 1.8×10 8CFU / g is composed of Bacillus subtilis and yeast in a live cell ratio of 2:1.

[0063] (5) The mixture is left to stand at 28°C for 7 days to obtain a mixed slurry;

[0064] (6) The mixed slurry is filtered by a plate and frame filter press, and the filtered liquid phase is the plant nutrient solution.

[0065] Plant nutrient solution composition detection experiment:

[0066] I. Detection of water-soluble organic matter content

[0067] According to NY / T 1971-2010, the potassium dichromate-sulfuric acid solution oxidation method was used for determination.

[0068] 1. Main reagents and instruments:

[0069] Instruments: Erlenmeyer flask (250mL), acid burette, adjustable electric furnace, fume hood.

[0070] Reagents: 0.4 mol / L potassium dichromate-sulfuric acid solution (weigh 40g potassium dichromate and dissolve it in 1L of water, then slowly add 1L of concentrated sulfuric acid while stirring), 0.2 mol / L ferrous sulfate standard solution, and o-phenanthroline indicator.

[0071] 2. Experimental methods:

[0072] Sample pretreatment: Shake the plant nutrient solution sample well; if there is any precipitate, filter it. Accurately pipette 2.0 mL of the sample into a 250 mL Erlenmeyer flask.

[0073] Oxidation: Accurately add 20.0 mL of 0.4 mol / L potassium dichromate-sulfuric acid solution to an Erlenmeyer flask and shake well. Cover the mouth of the flask with a small funnel, place it on a preheated electric stove, and boil for 10 minutes under boiling conditions.

[0074] Titration: After digestion and cooling, rinse the funnel and flask walls with an appropriate amount of water to control the total solution volume to approximately 100 mL. After cooling, add 3 drops of o-phenanthroline indicator and titrate with 0.2 mol / L ferrous sulfate standard solution. The endpoint is reached when the solution color changes from orange-yellow to blue-green to brown-red. Record the volume of ferrous sulfate consumed (V).

[0075] Blank experiment: Replace the sample with 2.0 mL of water, and perform the same steps as the sample. Record the volume of ferrous sulfate consumed (V0).

[0076] The water-soluble organic matter content was calculated based on the test results, and the results are shown in Table 1.

[0077] II. Detection of total nitrogen, phosphorus, and potassium nutrient content:

[0078] Accurately weigh 5.00g of the well-shaken nutrient solution sample into a Kjeldahl flask, add concentrated sulfuric acid and a mixed catalyst (copper sulfate + potassium sulfate), and digest in a digestion furnace until the solution turns a clear blue-green color. After cooling, dilute to 100mL in a volumetric flask to obtain the test solution.

[0079] Total nitrogen (N): The Kjeldahl method was used for nitrogen determination. The sample was digested with sulfuric acid to convert it into ammonium nitrogen, then distilled with alkali, absorbed with boric acid, and titrated with an acid standard solution.

[0080] Total phosphorus (P2O5): The vanadium-molybdate yellow colorimetric method was used. The sample was digested with sulfuric acid, and all phosphorus was converted into orthophosphate. Under acidic conditions, it formed a yellow complex with ammonium metavanadate and ammonium molybdate, which was then measured colorimetrically at a wavelength of 440 nm.

[0081] Total potassium (K2O): Flame photometry was used. After the sample was digested with sulfuric acid, potassium elements were excited in the flame and emitted light of a specific wavelength, the intensity of which was directly proportional to the potassium content. The test results are shown in Table 1.

[0082] III. Evaluation of Heavy Metal Lattice Fixation Rate / Effective State Removal Rate:

[0083] The speciation of heavy metals (using Cd as the standard) in samples before and after treatment was analyzed using the BCR three-step sequential extraction method. The heavy metals were classified into four speciations:

[0084] Acid-extractable form (F1): has the highest activity and is easily utilized by organisms.

[0085] Reducible state (F2): It combines with iron and manganese oxides and may be released when conditions change.

[0086] Oxidizable form (F3): It combines with organic matter and sulfides and is relatively stable.

[0087] Residual state (F4): Exists in the mineral lattice, is extremely stable, and is almost not utilized by organisms.

[0088] The essence of lattice fixation is to increase the proportion of residual state (F4).

[0089] 1. Experimental Method:

[0090] BCR extraction was performed on the original organic materials and the final nutrient solution precipitate (filtered residue) after treatment by the method of this invention.

[0091] F1 (Acid-extractable state): Take 0.50 g of sample, add 20 mL of glacial acetic acid (0.11 mol / L), shake at room temperature for 16 hours, centrifuge, and take the supernatant to determine the Cd content. Proceed to the next step for residues.

[0092] F2 (reducible state): Add 20 mL of hydroxylamine hydrochloride (0.5 mol / L, pH=1.5) to the residue from the previous step, shake at room temperature for 16 hours, centrifuge, and collect the supernatant. Proceed to the next step with the residue.

[0093] F3 (oxidizable state): Add 5 mL of hydrogen peroxide (30%, pH=2.3) to the residue from the previous step, incubate in a water bath at 85°C for 1 hour, and evaporate to near dryness. Then add 25 mL of ammonium acetate (1.0 mol / L, pH=2), shake at room temperature for 16 hours, centrifuge, and collect the supernatant.

[0094] F4 (residual state): The remaining residue was digested with aqua regia, and the Cd content was determined.

[0095] 2. Determination: The Cd concentration in the supernatant and digestion solution from each extraction step was determined using atomic absorption spectrometry (AAS) or inductively coupled plasma mass spectrometry (ICP-MS). The percentage of each Cd form in the total Cd was calculated. The lattice fixation rate was directly characterized by the percentage of residual states (F4%), and the results are shown in Table 1.

[0096] IV. Detection of Cypermethrin Residue:

[0097] Cypermethrin was extracted from the sample with acetonitrile, purified with QuEChERS purification material, and detected by liquid chromatography-tandem mass spectrometry (LC-MS / MS). Quantification was performed using the external standard method.

[0098] 1. Instruments and equipment:

[0099] The system is equipped with a liquid chromatography-tandem mass spectrometry (LC-MS / MS) instrument, an electrospray ionization source (ESI), an analytical balance (sensitivity 0.1 mg and 0.01 g), a high-speed homogenizer, a high-speed centrifuge (speed ≥ 10000 r / min), a vortex mixer, a nitrogen blower, and pipettes.

[0100] 2. Reagents and materials: Acetonitrile (chromatographic grade), methanol (chromatographic grade), acetic acid (chromatographic grade), sodium chloride (analytical grade), cypermethrin standard (purity ≥ 98%), QuEChERS purification tubes: containing 150 mg anhydrous magnesium sulfate (MgSO4), 50 mg primary and secondary amines (PSA), 50 mg C18 packing material, and microporous filter membrane (0.22 μm, PTFE material).

[0101] 3. Solution preparation:

[0102] Standard stock solution (100 mg / L): Accurately weigh an appropriate amount of cypermethrin standard (accurate to 0.1 mg), dissolve it in acetonitrile and dilute to volume, and store in a refrigerator at -18°C.

[0103] Series of standard working solutions: Before use, the stock solution is gradually diluted with blank sample matrix solution (prepared from blank samples without cypermethrin according to the sample pretreatment steps) to form a series of standard working solutions of appropriate concentrations (1.0, 5.0, 10.0, 50.0, 100.0 μg / L) for the preparation of standard curves.

[0104] 4. Sample pretreatment steps:

[0105] (1) Extraction: Accurately weigh 5.0 g (accurate to 0.01 g) of the subcritically treated hydrolysate sample into a 50 mL centrifuge tube. Add 10 mL of acetonitrile and 1 g of sodium chloride. Vortex vigorously for 2 minutes to ensure thorough mixing and extraction. Centrifuge at 10000 r / min for 5 minutes, allow to stand for separation, and wait for purification.

[0106] (2) Purification:

[0107] Accurately pipette 1.5 mL of the upper acetonitrile extract into a QuEChERS purification tube, vortex for 2 minutes to ensure full contact between the extract and the purification packing material, adsorbing impurities. Centrifuge at 10000 r / min for 5 minutes; accurately pipette 1.0 mL of the supernatant into a clean vial for LC-MS / MS analysis.

[0108] 5. Instrumental analysis conditions:

[0109] Chromatographic conditions: Column: C18 column (100 mm × 2.1 mm, 1.8 μm); Mobile phase: Phase A: 0.1% formic acid aqueous solution; Phase B: 0.1% formic acid acetonitrile solution; Column temperature: 40 ℃; Injection volume: 5 μL.

[0110] Mass spectrometry conditions: Ion source: electrospray ionization (ESI); Scan mode: negative ion scan; Detection mode: multiple reaction monitoring (MRM); Capillary voltage: 3.0 kV; Ion source temperature: 150 ℃; Desolvation gas temperature: 500 ℃; Desolvation gas flow rate: 1000 L / h.

[0111] Sample determination: The prepared sample solution was injected for analysis. Based on the obtained quantitative ion peak area, the concentration of cypermethrin in the sample solution was calculated by substituting it into the standard curve regression equation and converted into the residual amount of cypermethrin in the sample (mg / kg). The results are shown in Table 1.

[0112] Table 1. Results of Plant Nutrient Solution Composition Analysis

[0113] Water-soluble organic matter content Total nitrogen, phosphorus and potassium Heavy metal lattice fixation rate Cypermethrin residue (mg / kg) Example 1 35.2% 10.7% 99.2% 0.186 Example 2 31.9% 10.3% 98.8% 0.201 Example 3 29.4% 9.7% 99.1% 0.217 Example 4 33.6% 10.6% 99.1% 0.074 Example 5 28.5% 8.9% 98.6% 0.357 Pre-processed materials / / / 16.752

[0114] As can be seen from the test results of Examples 1 to 5 in Table 1, the present invention uses subcritical hydrolysis technology combined with nanocatalysis to hydrolyze agricultural by-product organic materials to obtain plant nutrient solution with a water-soluble organic matter content of more than 30%, total nitrogen, phosphorus and potassium nutrients (N+P2O5+K2O) > 9%, heavy metal lattice fixation rate of more than 99%, and significantly improves the hydrolysis efficiency of organic materials, which is a significant improvement.

[0115] A comparison of the cypermethrin residue detection results in Examples 1, 4, and 5 in Table 1 shows that when nano-titanium carbide is used alone as a nanocatalyst, the cypermethrin residue in Example 1 is 0.186 mg / kg, while the cypermethrin residue in Example 5, which uses nano-cerium dioxide alone, is 0.357 mg / kg. However, when the amount of nanocatalyst is exactly the same, the cypermethrin residue in Example 4, when both are used in combination, is 0.074 mg / kg. The pesticide residue removal rate is far superior to that when either is used alone. This demonstrates that nano-titanium carbide and nano-cerium dioxide in this invention have a significant synergistic effect in improving the subcritical hydrolysis pesticide residue removal rate of agricultural by-products.

Claims

1. A method for producing plant nutrient solution by subcritical hydrolysis coupled with nanocatalysis to degrade agricultural by-product organic materials, characterized in that, Includes the following steps: S1. Crush agricultural by-product organic materials to a particle size of 10-20cm to obtain pretreated materials; S2. Add 0.5% to 2% of a composite nanocatalyst, comprising nano-titanium carbide, to the pretreated material to obtain a mixture; S3. Place the mixture in a subcritical hydrolysis reactor to complete the subcritical hydrolysis reaction and obtain the hydrolysis product; S4. Add 1% to 3% of nano-humic acid and 0.1% to 0.5% of composite microbial agent by mass of the hydrolysis product to the hydrolysis product, stir and mix evenly to obtain a mixture. S5. Let the mixture stand at 25-35°C for 3-7 days to obtain a mixed slurry; S6. The liquid phase obtained by solid-liquid separation and filtration of the mixed slurry is the plant nutrient solution.

2. The method for producing plant nutrient solution by subcritical hydrolysis coupled with nanocatalysis for the degradation of agricultural by-products and organic materials according to claim 1, characterized in that: The composite nanocatalyst is composed of nano-titanium carbide and nano-cerium dioxide in a mass ratio of 1:0.1 to 0.

8.

3. The method for producing plant nutrient solution by subcritical hydrolysis coupled with nanocatalysis for the degradation of agricultural by-product organic materials according to claim 2, characterized in that: The particle size of the composite nanocatalyst is D50 = 15-80 nm.

4. The method for producing plant nutrient solution by subcritical hydrolysis coupled with nanocatalysis for the degradation of agricultural by-products and organic materials according to claim 2, characterized in that: In step S3, the subcritical hydrolysis reaction has a reaction temperature of 374.2℃, a reaction pressure of 22.1MPa, and a reaction time of 40–120s.

5. The method for producing plant nutrient solution by subcritical hydrolysis coupled with nanocatalysis for the degradation of agricultural by-product organic materials according to any one of claims 1 to 4, characterized in that: The compound microbial agent includes Bacillus subtilis and yeast, with a total viable count ≥1×10⁻⁶. 8 CFU / g.

6. The method for producing plant nutrient solution by subcritical hydrolysis coupled with nanocatalysis to degrade agricultural by-product organic materials according to claim 5, characterized in that: The ratio of viable Bacillus subtilis to yeast is 1.2–3:

1.

7. The method for producing plant nutrient solution by subcritical hydrolysis coupled with nanocatalysis for the degradation of agricultural by-product organic materials according to any one of claims 1 to 4, characterized in that: The nano-humic acid has a particle size D50 of 10–220 nm.

8. The method for producing plant nutrient solution by subcritical hydrolysis coupled with nanocatalysis for the degradation of agricultural by-product organic materials according to any one of claims 1 to 4, characterized in that: The solid-liquid separation method described in S6 is filtration by plate and frame filter press.

9. A plant nutrient solution prepared by the method for producing plant nutrient solution by subcritical hydrolysis coupled with nanocatalysis for degradation of agricultural by-product organic materials as described in any one of claims 1 to 8.

10. A method for planting crops, characterized in that: The step includes applying the plant nutrient solution as described in claim 9.