A method for harmless treatment and nutrient separation of waste corn stalks and preparation of green slow-release substrate

Abstract

The application discloses a harmless treatment and nutrient separation method of waste corn straw and preparation of green slow-release substrate, and belongs to the field of agricultural solid waste resource utilization. The method takes waste corn straw as raw material, and through the steps of crushing, green solvent ultrasonic-assisted extraction, multi-stage countercurrent extraction, concentration and drying, etc., the straw nutrients rich in protein, fat, carbohydrate and inorganic trace elements are efficiently separated and obtained. Further, the straw nutrients and inorganic fertilizer are mixed in a specific proportion, and the solid full-biodegradable nutrient slow-release substrate block is obtained through compression molding. The method provided by the application realizes full-component high-value utilization of the waste corn straw, and the prepared full-biodegradable nutrient slow-release substrate block can effectively replace traditional peat substrate, is a kind of modern agricultural production material with low cost, environmental friendliness and suitability for popularization, and has important significance for promoting the development of circular agriculture.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for harmless treatment and nutrient separation of waste corn stalks and preparation of green slow-release substrate, belonging to the field of agricultural solid waste resource utilization. BACKGROUND

[0002] As a solid agricultural waste, corn stalks have a huge annual output, and efficient resource utilization is the key way to solve straw burning pollution, promote agricultural waste value-added utilization, and develop circular agriculture. At present, corn stalks at the milky mature stage to the early wax mature stage can be directly used for silage feed because the soluble sugar content is ≥25% and the crude protein content is ≥7%. However, after the wax mature stage, the lignification degree of the stalks increases, and the feed value decreases, lacking an economically viable treatment method, and often being burned on site, leading to prominent seasonal air pollution. In fact, corn stalks not only contain structural components such as cellulose, hemicellulose, and lignin, but also are rich in protein, fat, carbohydrates, and various trace elements, making it a highly potential biomass resource.

[0003] Existing straw utilization methods mainly include whole utilization and component separation. Whole utilization methods such as direct pulverization and return to the field or feed production have simple processes but low added value. Component separation methods focus on extracting a single component (such as lignin or cellulose), but generally ignore the effective recovery of nutrients, resulting in resource waste. For example, existing technologies CN118077547A, CN108070621A, and CN117866227A focus on the extraction of specific components and fail to consider the efficient and coordinated utilization of whole components of straw, especially in the process of extracting cellulose or lignin. Strong acid and strong base treatment combined with high-temperature cooking or steam explosion are often used to break the lignin-carbohydrate complex, which fails to achieve non-destructive utilization of whole components, resulting in waste of overall resources and low utilization efficiency. In addition, some methods (such as CN108570482A) have a long processing period, and only the sealing storage stage requires 65 days, and after anaerobic fermentation, the whole process takes more than a month, which lacks economic efficiency and practicality.

[0004] Therefore, it is an urgent need in the field of agricultural waste resource utilization to develop a green technology that can synergistically recover nutrients and realize the value-added conversion of whole components of waste corn stalks. SUMMARY

[0005]

TECHNICAL PROBLEM

[0006] To develop a green technology that can synergistically recover nutrients and realize the value-added conversion of whole components of waste corn stalks, and realize agricultural waste resource utilization.

[0007]

TECHNICAL SCHEME

[0008] In view of the problems of low nutrient recovery rate, serious waste and dependence on non-renewable peat in the existing corn straw utilization technology, a green, efficient and low-cost method is provided for directional extraction of nutrients from waste corn straw and preparation of full-biodegradable seedling nutrient substrate blocks.

[0009] To achieve the above-mentioned purpose, the technical solution adopted by the present application is:

[0010] In a first aspect, the present application provides a method for harmless treatment and separation of nutrients from waste corn straw, comprising the following steps:

[0011] S1. Pretreatment: wash and dry the waste corn straw, cut into small pieces, crush, sieve, and control the powder particle size of the straw powder to be 80-120 mesh;

[0012] S2. Ultrasonic pretreatment: mix the straw powder of S1 with water, stir, and treat with ultrasonic waves under the conditions of 300-500 W, 25-40 kHz, 30-60℃ for 30-90 min to obtain pretreated slurry;

[0013] S3. Multistage countercurrent extraction: pump the pretreated slurry of S2 into a multistage countercurrent extraction system, use a 50%-70% volume fraction ethanol aqueous solution as an extractant for N-stage countercurrent extraction, N≥3; fresh extractant is used in each stage and is in countercurrent contact with the material of the adjacent stage; each stage of extraction is performed for 30-60 min at 60-70℃, the solid-liquid ratio is controlled to be 1:(4-8), and the extraction mixed liquid is obtained under the condition of not adding acid, base, salt or enzyme in the whole process

[0014] S4. Nutrient powder recovery: solid-liquid separation is performed on the extraction mixed liquid to collect the liquid phase, the liquid phase is concentrated to 1 / 4-1 / 5 of the original volume, and is dried under the conditions of-0.08- -0.10 MPa, 60-70℃ to obtain a nutrient powder with a water content of ≤5%.

[0015] In an embodiment of the present application, in S1, the water content of the washed and dried corn straw is less than 10%.

[0016] In an embodiment of the present application, in S1, the waste corn straw is cut into small pieces of 1-3 cm.

[0017] In an embodiment of the present application, in S2, the straw powder is mixed with water at a mass-volume ratio of 1:(5-20) and stirred for at least 0.5 h.

[0018] In an embodiment of the present application, in S3, the extraction is performed at 60-70℃.

[0019] In one embodiment of the present application, in S3, the solid-liquid ratio is controlled to be 1: (4-8).

[0020] In one embodiment of the present application, in S4, the obtained solid is used for further extraction of cellulose, lignin and hydrolysis to prepare xylose, arabinose and the like.

[0021] In one embodiment of the present application, in S4, the collected liquid is concentrated to 1 / 4-1 / 5 of the original volume, and then dried under the conditions of a vacuum degree of -0.08 to -0.10 MPa and a temperature of 60-70°C to obtain a nutrient powder with a water content of less than 5%.

[0022] In a second aspect, the present application provides a nutrient powder prepared based on the above method.

[0023] In a third aspect, the present application provides a nutrient slow-release substrate containing the nutrient powder and inorganic fertilizer.

[0024] In one embodiment of the present application, the nutrient slow-release substrate comprises the following components by weight percentage: 88-92% of the nutrient powder, 2-4% of potassium sulfate, 2-3% of ammonium dihydrogen phosphate, 1-2% of calcium superphosphate, 2-4% of urea, 0.5-1% of sodium carboxymethyl cellulose and 0.3-0.8% of polylactic acid.

[0025] The present application also provides a method for preparing the nutrient slow-release substrate, which comprises mixing the nutrient powder with potassium sulfate, ammonium dihydrogen phosphate, calcium superphosphate, urea, sodium carboxymethyl cellulose and polylactic acid, homogenizing after adding water, and then pressing to form the nutrient slow-release substrate.

[0026] Advantages

[0027] 1. Optimal utilization of resources: full component and cascade high-value utilization of corn stalks is achieved. Endogenous nutrients (protein, fat, carbohydrate, etc.) that are prone to loss are efficiently extracted first, with a yield of more than 10%, of which the protein content is ≥5%, the fat content is ≥2%, and the soluble carbohydrate content is ≥50%; the subsequent residue can still be used for separation and extraction of cellulose, lignin and other products, thereby fundamentally solving the problem of serious resource waste and low added value in traditional utilization methods, achieving "eating dry and squeezing dry", and the overall utilization rate being more than 95%.

[0028] 2. Green production process: The core process uses water and ethanol as solvents, which are non-toxic and recyclable. The ethanol recovery system achieves more than 95% solvent recovery and reuse, and the process is completed within 24 hours. Through ultrasonic pretreatment and multi-stage countercurrent extraction, the extraction efficiency and quality of heat-sensitive nutrients are significantly improved under mild conditions, completely avoiding secondary pollution and component degradation caused by strong acid, strong alkali and high temperature processes, thus avoiding environmental pollution problems. The entire process does not require the treatment of plant hydrolytic enzymes, pectinases, etc., which can effectively control costs.

[0029] 3. Functionalization of End Products: The prepared substrate blocks are not only a physical substitute for traditional peat, but also a functional slow-release nutrient carrier. Compared with peat substrate, plant height, root length, and stem base increased by 28%, 36%, and 33% respectively, and the survival rate reached 99%. Using the nutrients from waste corn stalks as its core, combined with inorganic fertilizers, it provides comprehensive nutrition and completely degrades and returns to the field after transplanting, truly achieving a seamless connection and ecological cycle between seedling cultivation and growth. Attached Figure Description

[0030] Figure 1 Example 3: Photographs of the nutrients obtained;

[0031] Figure 2 Example 3: Infrared spectra of nutrients were obtained. Detailed Implementation

[0032] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. Unless otherwise stated, to avoid repetition, embodiments 1 to 3 are operated under the following common conditions: fresh extractant is used in each countercurrent stage; extraction temperature is 60-70℃; solid-liquid ratio is 1:(4-8); each stage lasts 30-60 min; no acid, alkali, salt or enzyme is added throughout the process. Representative detection results: protein ≥5.0%, fat ≥2.0%, soluble carbohydrates ≥50% (detection method see

[0024] ). The reagents and raw materials used are all commercially available. The embodiments in this invention are only for explaining the invention and do not limit the invention in any way. Any changes or substitutions made based on this invention are within the protection scope of this invention.

[0033] The detection methods involved in the following examples are: NB / T 34057.8-2020 Determination of Chemical Components of Lignocellulosic Biomass Raw Materials - Part 8: Determination of Proteins; NB / T 34057.9-2020 Determination of Chemical Components of Lignocellulosic Biomass Raw Materials - Part 9: Determination of Lipids; NB / T 10767-2021 Determination of Chemical Components of Lignocellulosic Biomass Raw Materials - Part 4: Determination of Soluble Sugars.

[0034] Example 1 Extraction of components from discarded corn stalks

[0035] (1) The discarded corn stalks were washed, dried, cut into 1-2 cm pieces with a hay cutter, and then ground and passed through a 100 mesh sieve using a super micro grinder to obtain straw powder;

[0036] (2) 1 kg of the straw powder was mixed with 10 L of deionized water, and pre-stirred at 25°C and 300 rpm for 0.5 hours. Then it was transferred into an ultrasonic reactor, and treated at 300 W, 30 kHz, and 50°C for 60 minutes to obtain a slurry;

[0037] (3) The slurry was pumped into a three-stage countercurrent extraction tank, and fresh 65°C, 60% ethanol aqueous solution was used as the extractant in each stage. The solid-liquid ratio was controlled at 1:6, and the extraction time in each stage was 60 minutes;

[0038] (4) After the extraction was completed, solid-liquid separation was performed using a plate and frame filter press, and the extract was collected. About 58 L of extract was obtained, and about 875 g of solid residue (dry basis, weighed after drying at 105°C to constant weight) was obtained;

[0039] (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 (moisture content 3.9%), with a yield of 10.2%.

[0040] It was detected that the protein content in the powder was 5.8%, the fat content was 2.8%, and the soluble carbohydrate content (calculated as glucose) was 63.5%.

[0041] The entire reaction cycle from feeding to discharging was completed in ≤24 hours; the only reagent involved was 60% ethanol by volume, without the need for any acid, base or salt aids; the residual solid residue (cellulose, hemicellulose, etc.) in step (4) could be further utilized, ensuring that no secondary waste was generated. The process has an in-built ethanol recovery system, which can achieve a solvent recovery rate of more than 95%, significantly reducing operating costs and environmental load, and reducing the comprehensive treatment cost per ton of discarded corn stalks. This process route is simple and low in cost, and simultaneously achieves efficient and high-value recovery of discarded corn stalks.

[0042] Example 2 Extraction of components from discarded corn stalks

[0043] (1) The discarded corn stalks were washed, dried, cut into 1-2 cm pieces with a hay cutter, and then ground and passed through a 100 mesh sieve using a super micro grinder to obtain straw powder;

[0044] (2) 1 kg of the straw powder was mixed with 10 L of deionized water and stirred at 25 °C and 300 rpm for 0.5 h. Then, the mixture was transferred into an ultrasonic reactor and treated at 400 W, 40 kHz and 60 °C for 90 min to obtain a slurry;

[0045] (3) The slurry was pumped into a three-stage countercurrent extraction tank, and fresh 70 °C, 60% ethanol aqueous solution was used as the extractant in each stage. The solid-liquid ratio was controlled at 1:8, and the extraction time was 60 min in each stage;

[0046] (4) After the extraction, solid-liquid separation was performed by using a plate-and-frame filter press to collect the extract. About 72 L of the extract was obtained, and the solid residue was about 862 g (dry basis, weighed after drying at 105 °C to constant weight).

[0047] (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 (moisture content 4.2%), with a yield of 12.6%.

[0048] It was detected that the protein content in the powder was 5.3%, the fat content was 2.2%, and the soluble carbohydrate content (calculated as glucose) was 59.2%.

[0049] Example 3 Extraction of components from discarded corn straw

[0050] (1) The discarded corn straw was washed and dried, cut into 1-2 cm pieces by a grass cutter, and then crushed by a super micro grinder and passed through a 100-mesh sieve to obtain straw powder;

[0051] (2) 1 kg of the straw powder was mixed with 10 L of deionized water and stirred at 25 °C and 300 rpm for 0.5 h. Then, the mixture was transferred into an ultrasonic reactor and treated at 500 W, 40 kHz and 60 °C for 90 min to obtain a slurry;

[0052] (3) The slurry was pumped into a three-stage countercurrent extraction tank, and fresh 70 °C, 60% ethanol aqueous solution was used as the extractant in each stage. The solid-liquid ratio was controlled at 1:8, and the extraction time was 60 min in each stage;

[0053] (4) After the extraction, solid-liquid separation was performed by using a plate-and-frame filter press to collect the extract. About 72 L of the extract was obtained, and the solid residue was about 862 g (dry basis, weighed after drying at 105 °C to constant weight).

[0054] (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 (moisture content 4.2%), with a yield of 12.6%. Figure 1 ​

[0055] The protein content in the powder was 5.0%, the fat content was 2.1%, and the soluble carbohydrate content was 57.8% (calculated as glucose). As shown in Table 1, it was confirmed that the extracted nutrient powder was a complex mixture containing the three macronutrients of protein, lipid, and carbohydrate. Figure 2

[0056] Example 4 Reuse of Whole-component Nutrients

[0057] 900 g of the nutrient powder prepared by 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 were weighed. The mixture was mixed in a mixer for 20 minutes. Then, 200 ml of deionized water was added, and the mixture was homogenized at high speed for 4 minutes. The wet material after homogenization was filled into a mold and pressed to form a uniform specification of seedling nutrient substrate block under a pressure of 10 MPa.

[0058] Comparative Example 1 Extraction of components from discarded corn stalks

[0059] This comparative example uses oil bath heating instead of ultrasonic treatment, and the remaining steps are the same as Example 1.

[0060] 1 kg of corn stalk powder from the same batch was mixed with 10 L of water and heated in an oil bath at 90°C for 90 minutes, and the subsequent steps were the same as Example 1. Finally, 65 g of nutrient powder was obtained, with a yield of 6.5%, of which the protein content was 1.8%, the fat content was 0.7%, and the soluble carbohydrate content was 58.0% (calculated as glucose). High temperature can cause degradation of heat-sensitive nutrients, so the protein content and fat content are significantly reduced.

[0061] Comparative Example 2 Extraction of components from discarded corn stalks

[0062] This comparative example does not use ultrasonic treatment, and the remaining steps are the same as Example 1.

[0063] 1 kg of corn stalk powder from the same batch was mixed with 10 L of water and stirred at 25°C for 3 hours (without ultrasonic treatment). The subsequent extraction, solid-liquid separation, concentration, and drying conditions were exactly the same as in Example 1. Finally, 68 g of nutrient powder (dry basis, weighed after drying to constant weight at 105°C) was obtained, with a yield of 6.8%, of which the protein content was 2.1%, the fat content was 0.9%, and the soluble carbohydrate content was 52.5% (calculated as glucose).

[0064] This comparative example shows that omitting the ultrasonic pretreatment step, even if the subsequent extraction process is exactly the same, the extraction efficiency of nutrients will be greatly reduced, proving that ultrasonic pretreatment is an indispensable key step in this method.

[0065] ​Example 5 Extraction of abandoned corn straw components

[0066] The ultrasonic reaction time was set to 15, 40 or 65 minutes.

[0067] (1) After the abandoned corn straw was washed and dried, it was cut into 1-2 cm pieces using a hay cutter, then pulverized using a super micro pulverizer and passed through a 100 mesh sieve to obtain straw powder;

[0068] (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 hours. Then it was transferred into an ultrasonic reactor, treated at 500 W, 40 kHz, 60°C for 15, 40 or 65 minutes to obtain a slurry;

[0069] (3) The slurry was pumped into a three-stage countercurrent extraction tank, and fresh 70°C, 60% ethanol aqueous solution was used as the extractant in each stage, with a solid-liquid ratio of 1:8 and an extraction time of 60 minutes in each stage;

[0070] (4) After the extraction was completed, solid-liquid separation was performed using a plate and frame filter press, and the extract was collected.

[0071] (5) The extract was concentrated under reduced pressure, then dried in a vacuum drying oven (-0.09 MPa, 65°C) to obtain a brown nutrient powder.

[0072] The results showed that ultrasonic treatment for 15 minutes yielded 31 g of brown nutrient powder (with a water content of 3.4%), with a yield of 3.1%. The powder was detected to have a protein content of 4.3%, a fat content of 1.1%, and a soluble carbohydrate content of 43.5% (calculated as glucose).

[0073] Ultrasonic treatment for 40 minutes yielded 69 g of brown nutrient powder (with a water content of 3.6%), with a yield of 6.9%. The powder was detected to have a protein content of 4.9%, a fat content of 1.8%, and a soluble carbohydrate content of 57.4% (calculated as glucose).

[0074] Ultrasonic treatment for 65 minutes yielded 116 g of brown nutrient powder (with a water content of 3.3%), with a yield of 11.6%. The powder was detected to have a protein content of 5.2%, a fat content of 2.0%, and a soluble carbohydrate content of 58.9% (calculated as glucose).

[0075] Example 6 Practical use of the seedling raising nutrient substrate block

[0076] The rice seeds after germination were sowed in the seedling raising nutrient substrate blocks prepared in Example 4. The same amount of common conventional peat substrate (Pin peat) on the market was used as a control group, and 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 were mixed in each 1 kg of the conventional peat substrate (Pin peat).

[0077] Cultivation under the same environment and management conditions: the two groups of seedling trays were placed in the same greenhouse, and were cultivated under the same light cycle (12 h light / 12 h darkness), temperature (day temperature 28±2℃, night temperature 22±2℃), and humidity (50%±5%) conditions, and were irrigated once a day, and were detected after 18 days of cultivation.

[0078] Table 1

[0079] Plant height (cm) Root length (cm) Stem base width (cm) Survival rate Nutrient medium experimental group 15.8 8.7 2.8 99% Peat medium control group 12.3 6.4 2.1 92%

[0080] As can be seen from the results in Table 1, the seedling quality (plant height, root length, and stem base width) and survival rate of the nutrient substrate blocks of the present application are significantly better than those of the peat substrate. After transplanting, the substrate blocks of the present application begin to degrade in the soil after about 40 days, and are completely degraded after 60 days. It is detected that the degradation products are harmless to the environment, and can improve soil fertility.

[0081] The above description is only an embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent transformation or direct or indirect application in the related technical field using the content of the present application is also included in the patent protection scope of the present application.

Claims

1. A slow-release nutrient substrate for rice seedling cultivation, characterized in that, The nutrient powder is extracted from waste corn stalks; The nutrient slow-release substrate comprises the following components by weight percentage: 88-92% of the nutrient powder, 2-4% of potassium sulfate, 2-3% of ammonium dihydrogen phosphate, 1-2% of calcium superphosphate, 2-4% of urea, 0.5-1% of sodium carboxymethyl cellulose, and 0.3-0.8% of polylactic acid; The soluble carbohydrate content in the nutrient powder is greater than or equal to 57.8%, the protein content is greater than or equal to 5.0%, and the fat content is greater than or equal to 2.1%. The preparation method of the nutrient powder comprises the following steps: S1. Pretreatment: washing and drying the waste corn stalks, cutting them into small pieces, crushing, sieving, and controlling the powder particle size of the stalk powder to be 80-120 mesh; S2. Ultrasonic pretreatment: mixing the stalk powder of S1 with water, stirring, and performing ultrasonic treatment at 300-500 W, 25-40 kHz, and 30-60 ℃ for 30-90 min to obtain a pretreated slurry; S3. Multistage countercurrent extraction: pumping the pretreated slurry of S2 into a multistage countercurrent extraction system, using a 50-70% volume concentration of ethanol aqueous solution as an extractant to perform N-stage countercurrent extraction, each stage for 30-60 min, N≥3, to obtain an extraction mixture; S4. Nutrient powder extraction: performing solid-liquid separation on the extraction mixture of S3, collecting the liquid, concentrating, and drying to obtain the nutrient powder; In step S2, the stalk powder is mixed with water at a mass-to-volume ratio of 1:(5-15) and stirred for at least 0.5 h.

2. The nutrient slow-release substrate for rice seedling raising according to claim 1, characterized in that, In S3, the extraction is performed at 60-70 ℃; In S3, the solid-to-liquid ratio is controlled to be 1:(4-8).

3. The nutrient slow-release substrate for rice seedling raising according to claim 1, characterized in that, In step S4, the collected liquid is concentrated to 1 / 4-1 / 5 of the original volume.

4. The nutrient slow-release substrate for rice seedling raising according to claim 1, characterized in that, In step S4, the nutrient powder with a water content of less than 5% is obtained by drying at a vacuum degree of -0.08 to -0.10 MPa and a temperature of 60-70 ℃.

5. The nutrient slow-release substrate for rice seedling raising according to claim 1, characterized in that, In step S1, the water content of the washed and dried corn stalks is less than 10%; and the waste corn stalks are cut into small pieces of 1-3 cm.

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