Method for harmless treatment of waste corn straw, separation of nutrients and preparation of green slow-release matrix

Abstract

The invention discloses a method for harmlessly treating waste corn straws to separate nutrients and preparing a green slow-release matrix, and belongs to the field of recycling of agricultural solid wastes. According to the method, waste corn straw is used as a raw material, and straw nutrients rich in protein, fat, carbohydrate and inorganic trace elements are efficiently separated and obtained through the steps of smashing, green solvent ultrasonic-assisted extraction, multistage counter-current extraction, concentration, drying and the like. And further mixing the straw nutrient with an inorganic fertilizer according to a specific ratio, and carrying out compression molding to obtain the solid full-biodegradable nutrient slow-release matrix block. According to the method provided by the invention, all-component high-value utilization of the waste corn straws is realized, and the prepared full-biodegradable nutrient slow-release matrix block can effectively replace a traditional peat matrix, is a modern agricultural production material which is low in cost, environment-friendly and suitable for popularization, and has important significance on promoting circular agricultural development.

Description

Technical Field

[0001] The invention relates to a method for harmlessly treating waste corn stalks to separate nutrients and prepare a green slow-release matrix, belonging to the field of agricultural solid waste resource utilization. Background Art

[0002] Corn straw, as a solid agricultural waste, has a huge annual output. Its efficient resource utilization is a key way to solve the pollution caused by straw burning, promote the value-added utilization of agricultural waste, and develop circular agriculture. At present, corn straw from the late milky stage to the early waxy stage can be directly used as silage because of its soluble sugar ≥25% and crude protein ≥7%. However, after waxy maturity, the degree of lignification of the straw increases, and its feeding value decreases. There is a lack of economically feasible treatment methods, and it is often burned on site, resulting in prominent seasonal air pollution problems. In fact, corn straw not only contains structural components such as cellulose, hemicellulose and lignin, but is also rich in protein, fat, carbohydrates and various trace elements. It is a biomass resource with great development potential.

[0003] Existing straw utilization methods primarily fall into two categories: overall utilization and component separation. Overall utilization methods, such as direct crushing and returning to the field or making feed, offer simple processes but low added value. Component separation methods, on the other hand, focus on extracting a single component (such as lignin or cellulose), but generally neglect the effective recovery of nutrients, resulting in resource waste. For example, existing methods such as CN118077547A, CN108070621A, and CN117866227A focus on extracting specific components, failing to comprehensively consider the efficient and synergistic utilization of all straw components. In particular, during the extraction of cellulose or lignin, strong acid or alkali treatments combined with high-temperature cooking or steam explosion to break down the lignin-carbohydrate complexes fail to achieve the complete, non-destructive utilization of all components, leading to overall resource waste and low efficiency. Furthermore, some methods (such as CN108570482A) have excessively long processing cycles, requiring 65 days for the sealed storage stage alone, followed by anaerobic fermentation, a total process time exceeding one month, making them inefficient and unsuitable for both cost-effectiveness and practicality.

[0004] Therefore, the development of a green technology that can synergistically recycle nutrients and achieve value-added transformation of all components of waste corn straw has become an urgent need in the current field of agricultural waste resource utilization. Summary of the Invention

[0005]

Technical Issues

[0006]

Technical solution

[0007] To achieve the above object, the technical solution adopted by the present invention is: In a first aspect, the present invention provides a method for separating nutrients by harmlessly treating waste corn stalks, comprising the following steps: S1. Pretreatment: Wash and dry the discarded corn stalks, cut them into small pieces, crush them, and sieve them to a powder size of 80-120 mesh. S2. Ultrasonic pretreatment: Mix the straw powder from S1 with water, stir, and ultrasonicate for 30-90 min at 300-500 W, 25-40 kHz, and 30-60°C to obtain a pretreated slurry. S3. Multi-stage countercurrent extraction: The pretreated slurry from S2 is pumped into a multi-stage countercurrent extraction system. N stages of countercurrent extraction are performed using a 50% to 70% ethanol aqueous solution as the extractant. Each stage lasts 30 to 60 minutes, with N ≥ 3 extractions, to obtain an extract mixture. S4. Nutrient powder extraction: The extracted mixed solution of S3 is subjected to solid-liquid separation, the liquid is collected, concentrated and dried to obtain nutrient powder.

[0008] In one embodiment of the present invention, in S1, the moisture content of the washed and dried corn stalks is less than 10%.

[0009] In one embodiment of the present invention, in S1, the waste corn stalks are cut into small segments of 1 to 3 cm.

[0010] In one embodiment of the present invention, in S2, straw powder and water are mixed at a mass-to-volume ratio of 1:(5-20) and stirred for at least 0.5 h.

[0011] In one embodiment of the present invention, in S3, the extraction is performed at 60-70°C.

[0012] In one embodiment of the present invention, in S3, the solid-liquid ratio is controlled to be 1:(4-8).

[0013] In one embodiment of the present invention, in S4, the separated solid is used for further extraction of cellulose and lignin and hydrolysis to produce xylose, arabinose, etc.

[0014] In one embodiment of the present invention, in S4, the collected liquid is concentrated to 1 / 4 to 1 / 5 of the original volume, and then dried under vacuum conditions of -0.08 to -0.10 MPa and a temperature of 60 to 70° C. to obtain a nutrient powder with a moisture content of less than 5%.

[0015] In a second aspect, the present invention provides nutrient powder prepared based on the above method.

[0016] In a third aspect, the present invention provides a nutrient slow-release matrix comprising the nutrient powder and inorganic fertilizer.

[0017] In one embodiment of the present invention, the nutrient sustained-release matrix comprises the following components: by weight percentage, 88% to 92% of the nutrient powder, 2% to 4% potassium sulfate, 2% to 3% diammonium phosphate, 1% to 2% superphosphate, 2% to 4% urea, 0.5% to 1% sodium carboxymethyl cellulose and 0.3% to 0.8% polylactic acid.

[0018] The present invention also provides a method for preparing the nutrient sustained-release matrix, comprising mixing the nutrient powder with potassium sulfate, ammonium dihydrogen phosphate, calcium superphosphate, urea, sodium carboxymethyl cellulose and polylactic acid, adding water for homogenization and then pressing and molding to obtain the nutrient sustained-release matrix.

[0019] Beneficial effects 1. Optimized Resource Utilization: This system achieves high-value utilization of all components of corn stalks, achieving a tiered, high-value utilization. It pioneered the efficient extraction of easily lost endogenous nutrients (protein, fat, carbohydrates, etc.), achieving a yield exceeding 10%, with protein content ≥5%, fat ≥2%, and soluble carbohydrates ≥50%. The residue can then be used to separate and extract products such as cellulose and lignin, fundamentally resolving the severe resource waste and low added value inherent in traditional utilization methods. This system achieves "full utilization" and an overall utilization rate exceeding 95%.

[0020] 2. Green production process: The core process uses water and ethanol as solvents, which are non-toxic and recyclable. The ethanol recovery system can achieve more than 95% recovery and reuse of the solvent, and the process flow is controlled to be completed within 24 hours. Ultrasonic pretreatment and multi-stage countercurrent extraction are used to significantly improve the extraction efficiency and quality of heat-sensitive nutrients under mild conditions, completely avoiding secondary pollution and component degradation caused by strong acid, strong alkali, and high temperature processes, and avoiding environmental pollution problems. No plant hydrolase, pectinase, etc. are required throughout the process, which can effectively control costs.

[0021] 3. Functionalized End Product: The prepared matrix blocks are not only a physical substitute for traditional peat but also a functional, slow-release nutrient carrier. Compared to peat moss, they increase plant height, root length, and stem base by 28%, 36%, and 33%, respectively, with a 99% survival rate. Using the nutrients inherent in discarded corn stalks as a core, combined with inorganic fertilizer, they provide comprehensive nutrition and are completely degraded and returned to the field after transplanting, truly achieving a seamless "seedling-to-growth" cycle and an ecological cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Example 3 obtains photos of nutrients; Figure 2 Example 3 Obtain infrared spectra of nutrients. DETAILED DESCRIPTION

[0023] The technical scheme of the present invention is described in further detail below in conjunction with specific embodiments. Unless otherwise specified, the reagents and raw materials used in the embodiments can be purchased from the market. The embodiments in the present invention are only for explanation of the present invention, but are not limited to the present invention in any way. Any conversion or replacement made based on the present invention all falls within the scope of protection of the present invention.

[0024] The detection methods involved in the following examples: "NB / T 34057.8-2020 Determination of the chemical composition of lignocellulosic biomass raw materials Part 8: Determination of protein"; "NB / T 34057.9-2020 Determination of the chemical composition of lignocellulosic biomass raw materials Part 9: Determination of lipids"; "NB / T 10767-2021 Determination of the chemical composition of lignocellulosic biomass raw materials Part 4: Determination of soluble sugars".

[0025] Example 1 Extraction of components from waste corn stalks (1) Wash and dry the discarded corn stalks, cut them into 1-2 cm segments with a straw chopper, and then grind them with an ultrafine grinder and pass them through a 100-mesh sieve to obtain straw powder; (2) 1 kg of straw powder was mixed with 10 L of deionized water and pre-stirred at 25°C and 300 rpm for 0.5 h. The mixture was then transferred to an ultrasonic reactor and treated at 300 W, 30 kHz, and 50°C for 60 min to obtain a slurry. (3) The slurry is pumped into a three-stage countercurrent extraction tank. Fresh 60% ethanol aqueous solution at 65°C is used as the extractant in each stage. The solid-liquid ratio is controlled at 1:6, and the extraction time for each stage is 60 minutes. (4) After the extraction is completed, solid-liquid separation is performed using a plate and frame filter press, and the extract is collected. Approximately 58 L of extract and approximately 875 g of solid residue are obtained (dry basis, after drying at 105°C to constant weight and then weighing); (5) The extract was concentrated under reduced pressure to about 12 L and then dried in a vacuum drying oven (-0.09 MPa, 65°C) to obtain 102 g of brown nutrient powder (water content 3.9%) with a yield of 10.2%.

[0026] After testing, the powder contained 5.8% protein, 2.8% fat, and 63.5% soluble carbohydrates (calculated as glucose).

[0027] The entire reaction cycle, from feeding to discharging, takes ≤24 h. The only reagent involved is 60% ethanol by volume, without the need for any acid, alkali, or salt additives. The solid residue (cellulose, hemicellulose, etc.) remaining in step (4) can be further utilized to ensure that no secondary waste is generated. The process has a built-in ethanol recovery system, which can achieve over 95% solvent recovery and reuse, significantly reducing operating costs and environmental load, and lowering the overall processing cost per ton of waste corn straw. This process route is simple and low-cost, and simultaneously achieves efficient and high-value recovery of waste corn straw.

[0028] Example 2 Extraction of components from waste corn stalks (1) Wash and dry the discarded corn stalks, cut them into 1-2 cm segments with a straw chopper, and then grind them with an ultrafine grinder and pass them through a 100-mesh sieve to obtain straw powder; (2) 1 kg of straw powder was mixed with 10 L of deionized water and pre-stirred at 25°C and 300 rpm for 0.5 h. The mixture was then transferred to an ultrasonic reactor and treated at 400 W, 40 kHz, and 60°C for 90 min to obtain a slurry. (3) The slurry is pumped into a three-stage countercurrent extraction tank. Fresh 70°C, 60% ethanol aqueous solution is used as the extractant in each stage. The solid-liquid ratio is controlled at 1:8, and the extraction time for each stage is 60 minutes. (4) After the extraction, solid-liquid separation was performed using a plate-and-frame filter press, and the extract was collected. Approximately 72 L of extract and approximately 862 g of solid residue were obtained (dry basis, after drying at 105°C to constant weight and then weighing).

[0029] (5) The extract was concentrated under reduced pressure to about 12 L and then dried in a vacuum drying oven (-0.09 MPa, 65°C) to obtain 126 g of brown nutrient powder (water content 4.2%) with a yield of 12.6%.

[0030] After testing, the powder contained 5.3% protein, 2.2% fat, and 59.2% soluble carbohydrates (calculated as glucose).

[0031] Example 3 Extraction of components from waste corn stalks (1) Wash and dry the discarded corn stalks, cut them into 1-2 cm segments with a straw chopper, and then grind them with an ultrafine grinder and pass them through a 100-mesh sieve to obtain straw powder; (2) 1 kg of straw powder was mixed with 10 L of deionized water and pre-stirred at 25°C and 300 rpm for 0.5 h. The mixture was then transferred to an ultrasonic reactor and treated at 500 W, 40 kHz, and 60°C for 90 min to obtain a slurry. (3) The slurry is pumped into a three-stage countercurrent extraction tank. Fresh 70°C, 60% ethanol aqueous solution is used as the extractant in each stage. The solid-liquid ratio is controlled at 1:8, and the extraction time for each stage is 60 minutes. (4) After the extraction is completed, solid-liquid separation is performed using a plate and frame filter press, and the extract is collected. Approximately 74 L of extract and approximately 834 g of solid residue are obtained (dry basis, after drying at 105°C to constant weight and then weighing); (5) The extract was concentrated to about 12 L under reduced pressure and then dried in a vacuum drying oven (-0.09 MPa, 65°C) to obtain Figure 1 The brown nutrient powder shown is 147 g (water content 3.6%), with a yield of 14.7%.

[0032] After testing, the powder contains 5.0% protein, 2.1% fat, and 57.8% soluble carbohydrates (calculated as glucose). Figure 2 As shown, it is confirmed that the extracted nutrient powder is a complex mixture of three types of macronutrients: protein, lipid and carbohydrate.

[0033] Example 4 Recycling of all nutrients Weigh 900 g of the nutrient powder prepared using the method of Example 3, 30 g of potassium sulfate, 25 g of ammonium dihydrogen phosphate, 15 g of calcium superphosphate, 35 g of urea, 8 g of sodium carboxymethyl cellulose, and 5 g of polylactic acid. Mix in a mixer for 20 minutes. Then add 200 ml of deionized water and homogenize at high speed for 4 minutes. Fill the homogenized wet material into a mold and press-form at a pressure of 10 MPa to obtain a uniformly sized nutrient matrix block for growing seedlings.

[0034] Comparative Example 1 Extraction of components from waste corn straw In this comparative example, oil bath heating was used instead of ultrasonic treatment, and the remaining steps were the same as those in Example 1.

[0035] 1 kg of corn straw powder from the same batch was mixed with 10 L of water and heated in a 90°C oil bath for 90 minutes. The subsequent extraction process was the same as in Example 1. The final product was 65 g of nutrient powder with a yield of 6.5%, containing 1.8% protein, 0.7% fat, and 58.0% soluble carbohydrates (calculated as glucose). High temperatures may cause degradation of heat-sensitive nutrients, resulting in a significant decrease in both protein and fat content.

[0036] Comparative Example 2: Extraction of components from waste corn stalks This comparative example was not subjected to ultrasonic treatment, and the remaining steps were the same as those in Example 1.

[0037] 1 kg of corn straw powder from the same batch was mixed with 10 L of water and stirred at 25°C for 3 hours (without ultrasonic treatment). Subsequent extraction, solid-liquid separation, concentration, and drying conditions were identical to those in Example 1. The resulting nutrient powder (68 g, dry basis, after drying at 105°C to constant weight and weighing) had a yield of 6.8%, including 2.1% protein, 0.9% fat, and 52.5% soluble carbohydrates (calculated as glucose).

[0038] This comparative example shows that if the ultrasonic pretreatment step is omitted, the extraction efficiency of nutrients will drop significantly even if the subsequent extraction process is exactly the same, which proves that ultrasonic pretreatment is an indispensable key step in this method.

[0039] Example 5 Extraction of components from waste corn stalks Set the ultrasonic reaction time to 15, 40, or 65 minutes.

[0040] (1) Wash and dry the discarded corn stalks, cut them into 1-2 cm segments with a straw chopper, and then grind them with an ultrafine grinder and pass them through a 100-mesh sieve to obtain straw powder; (2) 1 kg of straw powder was mixed with 10 L of deionized water and pre-stirred at 25°C and 300 rpm for 0.5 h. The mixture was then transferred to an ultrasonic reactor and treated at 500 W, 40 kHz, and 60°C for 15, 40, or 65 min to obtain a slurry. (3) The slurry is pumped into a three-stage countercurrent extraction tank. Fresh 70°C, 60% ethanol aqueous solution is used as the extractant in each stage. The solid-liquid ratio is controlled at 1:8, and the extraction time for each stage is 60 minutes. (4) After the extraction is completed, use a plate and frame filter press to separate the solid and liquid and collect the extract.

[0041] (5) The extract was concentrated under reduced pressure and then dried in a vacuum drying oven (-0.09 MPa, 65°C) to obtain a brown nutrient powder.

[0042] The results showed that after 15 minutes of ultrasonication, 31 g of brown nutrient powder (3.4% water content) was obtained, with a yield of 3.1%. Testing showed that the powder contained 4.3% protein, 1.1% fat, and 43.5% soluble carbohydrates (calculated as glucose).

[0043] After 40 minutes of ultrasonic treatment, 69 g of brown nutrient powder (3.6% water content) was obtained, with a yield of 6.9%. Testing revealed that the powder contained 4.9% protein, 1.8% fat, and 57.4% soluble carbohydrates (calculated as glucose).

[0044] After 65 minutes of ultrasonic treatment, 116 g of brown nutrient powder (3.3% water content) was obtained, with a yield of 11.6%. Testing revealed that the powder contained 5.2% protein, 2.0% fat, and 58.9% soluble carbohydrates (calculated as glucose).

[0045] Example 6 Practical Utilization of Nutrient Matrix Blocks for Raising Seedlings The seedling trays were filled with the seedling nutrient matrix blocks prepared in Example 4, and the germinated rice seeds were sown. An equal amount of a commercially available traditional peat matrix (Pin's peat) was used as a control group. Per 1 kg of this traditional peat matrix (Pin's peat) was mixed with 30 g of potassium sulfate, 25 g of monoammonium phosphate, 15 g of superphosphate, 35 g of urea, 8 g of sodium carboxymethyl cellulose, and 5 g of polylactic acid.

[0046] Cultivate under the same environment and management conditions: Place the two groups of seedling trays in the same greenhouse and cultivate under the same light cycle (12h light / 12h dark), temperature (day temperature 28±2℃, night temperature 22±2℃) and humidity (50%±5%). Irrigate once a day and test after 18 days of cultivation.

[0047] Table 1 Plant height (cm) Root length (cm) Stem base width (cm) Survival rate Nutrient matrix experimental group 15.8 8.7 2.8 99% Peat substrate control group 12.3 6.4 2.1 92% The results in Table 1 show that the nutrient matrix blocks of the present invention significantly outperformed peat matrix in terms of seedling quality (plant height, root length, and stem base width) and survival rate. After transplanting, the matrix blocks of the present invention began to degrade in the soil after approximately 40 days and were completely degraded after 60 days. Testing confirmed that the degradation products were environmentally friendly and improved soil fertility.

[0048] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention specification, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for separating nutrients by harmlessly treating waste corn stalks, characterized in that: The steps are as follows: S1. Pretreatment: Wash and dry the discarded corn stalks, cut them into small pieces, crush them, and sieve them to a powder size of 80-120 mesh. S2. Ultrasonic pretreatment: Mix the straw powder from S1 with water, stir, and ultrasonicate for 30-90 min at 300-500 W, 25-40 kHz, and 30-60°C to obtain a pretreated slurry. S3. Multi-stage countercurrent extraction: The pretreated slurry from S2 is pumped into a multi-stage countercurrent extraction system. N stages of countercurrent extraction are performed using a 50% to 70% ethanol aqueous solution as the extractant. Each stage lasts 30 to 60 minutes, with N ≥ 3 extractions, to obtain an extract mixture. S4 nutrient powder extraction: The extraction mixture of S3 was subjected to solid-liquid separation, the liquid was collected, concentrated and dried to obtain a nutrient powder; In S2, straw powder and water were mixed at a mass-to-volume ratio of 1:(5-15) and stirred for at least 0.5 h; In S3, extraction was performed at 60–70 °C; In S3, the solid-liquid ratio is controlled to be 1:(4~8); In S4, the collected liquid is concentrated to 1 / 4 to 1 / 5 of the original volume; In S4, drying is performed under vacuum conditions of -0.08 to -0.10 MPa and a temperature of 60 to 70°C to obtain a nutrient powder having a moisture content of less than 5%; The nutrient powder has a protein content of ≥5.0% and a fat content of ≥2.1%.

2. The method according to claim 1, characterized in that In S1, the moisture content of the washed and dried corn straw was less than 10%; the discarded corn straw was cut into small segments of 1 to 3 cm.

3. The nutrient powder prepared according to any one of claims 1 to 2.

4. A nutrient slow-release matrix, characterized in that: Contains the nutrient powder according to claim 3 and inorganic fertilizer.

5. The nutrient slow-release matrix according to claim 4, characterized in that The nutrient sustained-release matrix comprises the following components: by weight percentage, 88% to 92% of the nutrient powder, 2% to 4% of potassium sulfate, 2% to 3% of ammonium dihydrogen phosphate, 1% to 2% of superphosphate, 2% to 4% of urea, 0.5% to 1% of sodium carboxymethyl cellulose and 0.3% to 0.8% of polylactic acid.

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