Potassium hydroxide and urea combined pretreatment method for improving composting efficiency and application

Abstract

The invention discloses a potassium hydroxide and urea combined pretreatment method for improving composting efficiency and application. The method comprises the following steps: mixing the agricultural waste with a mixed aqueous solution containing potassium hydroxide and urea at the same time, and treating under a heating condition to destroy the lignocellulose structure of the agricultural waste. According to the method, through the synergistic effect of potassium hydroxide and urea, lignin can be selectively and efficiently removed, and meanwhile cellulose is reserved to the maximum extent. The pretreated material is composted, so that the composting temperature rise can be obviously accelerated, the decomposition period is shortened, and the high-quality organic fertilizer which is high in decomposition degree and rich in potassium and nitrogen nutrients is produced. In addition, nutrient-rich filtrate generated in the pretreatment process can be recycled as a liquid fertilizer, so that full-chain resource utilization of agricultural wastes is realized.

Description

A combined pretreatment method of potassium hydroxide and urea for improving composting efficiency and its application Technical Field

[0001] This invention relates to the technical field of agricultural waste resource utilization and fertilizer preparation, specifically to a method and application of combined pretreatment with potassium hydroxide and urea to improve composting efficiency. Background Technology

[0002] The resource utilization of agricultural waste (such as various crop straws) is a key link in achieving sustainable agricultural development and a circular economy. This type of waste is mainly composed of lignocellulose, in which cellulose and hemicellulose are tightly bound by a complex three-dimensional network formed by lignin, constituting a natural biological barrier against degradation. This stubborn structure is the fundamental reason why its natural decomposition or traditional composting process is lengthy, has low maturity, and produces inconsistent product quality.

[0003] To overcome this barrier, various pretreatment methods have been extensively studied to disrupt the structure of lignocellulose. Chemical methods, especially alkali treatment, are widely used because they can effectively break the bonds between lignin and carbohydrates. However, while pursuing efficient lignin removal, existing technologies often face a dilemma: for example, strong alkali treatment (such as high-concentration KOH or NaOH) can powerfully destroy lignin, but inevitably leads to a significant hydrolysis loss of the target product—cellulose, reducing the overall retention rate of the solid matrix and the potential for subsequent resource utilization. Simultaneously, the strong alkaline environment is highly corrosive to equipment, requiring large amounts of water for neutralization and washing, resulting in costly high-salt wastewater treatment and creating a new environmental burden.

[0004] While ammoniation (such as the thermal decomposition of ammonia by urea) has a relatively mild mechanism and causes less damage to the cellulose structure, its delignification efficiency is limited and it does not completely break down the dense lignocellulose structure. Therefore, it is difficult to achieve a leapfrog improvement in the bioavailability of materials on its own, and the pretreatment effect is unstable.

[0005] More importantly, existing pretreatment studies mostly focus on serving a single downstream conversion pathway (such as enzymatic saccharification or anaerobic digestion). Their optimization objectives (such as maximizing accessible surface area or fermentable sugar yield) are systematically mismatched with the actual needs of the complex biological process of aerobic composting. The composting process not only requires the material to be degradable, but also requires it to have a suitable physical structure for microbial colonization (porosity, water retention), a balanced initial nutrient element (C / N ratio, potassium content), and low biotoxicity. Existing pretreatment technologies suffer from three main interconnected limitations: First, in terms of design objectives, they are often disconnected from the actual needs of aerobic composting processes, lacking a synergistic consideration of the evolution of material properties throughout the entire "pretreatment-composting" chain; second, in terms of treatment results, it is often difficult to balance the removal of lignin and the retention of the fiber skeleton, which can easily lead to damage to the pore structure of the compost pile, imbalance of key nutrient ratios, or the generation of microbial inhibitors; finally, in terms of resource management, pretreatment hydrolysate rich in potassium and nitrogen is generally regarded as "wastewater" to be treated, failing to integrate it as a liquid nutrient resource for reuse in agricultural systems, which wastes resources and reduces the overall environmental benefits of the process.

[0006] Therefore, developing a pretreatment and subsequent utilization technology that can synergistically overcome the lignin barrier, selectively retain the cellulose skeleton, simultaneously optimize the compostability of materials, and achieve closed-loop recovery of nutrients from process waste liquid is a pressing technical challenge in the field of high-value resource treatment of agricultural waste. Summary of the Invention

[0007] The main objective of this invention is to overcome the above-mentioned defects of the prior art and provide a method and application of combined pretreatment with potassium hydroxide and urea to improve composting efficiency. Through the synergistic effect of potassium hydroxide and urea, lignin can be selectively and efficiently removed while retaining cellulose to the maximum extent.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A method for combined pretreatment of potassium hydroxide and urea to improve composting efficiency includes the following steps: mixing the agricultural waste with a pretreatment solution and subjecting it to heat treatment; wherein the pretreatment solution is a mixed aqueous solution containing both potassium hydroxide and urea.

[0010] In this invention, the agricultural waste is sugarcane leaves, and the pretreatment solution contains potassium hydroxide at a mass concentration of 1.5%-4.0%, urea at a mass concentration of 1.0%-3.0%, a heating temperature of 60-95℃, and a treatment time of 0.5-4 hours.

[0011] In this invention, the pretreatment solution has a potassium hydroxide mass concentration of 2.5%, a urea mass concentration of 1.5%, a heating temperature of 80°C, and a treatment time of 2 hours.

[0012] The present invention also proposes a method for preparing decomposed organic fertilizer, comprising the following steps: S1: treating sugarcane leaves using the pretreatment method described above to obtain pretreatment residue; S2: mixing the pretreatment residue with livestock and poultry manure, adjusting the initial carbon-nitrogen ratio to 20-30:1, and carrying out aerobic composting.

[0013] In this invention, the livestock and poultry manure is cow manure, the initial carbon-nitrogen ratio is 25:1, and the initial moisture content of the compost material is 60%-70%.

[0014] The present invention also proposes an organic fertilizer prepared by the method described above.

[0015] The present invention also proposes the application of a composition of potassium hydroxide and urea as a pretreatment agent for sugarcane leaf composting. The pretreatment is achieved by reacting a mixed aqueous solution containing the composition with sugarcane leaves under heating conditions.

[0016] In summary, due to the adoption of the above technical solutions, the present invention has at least the following beneficial effects:

[0017] 1. This invention utilizes the synergistic effect of potassium hydroxide and urea under heating conditions. The strongly alkaline environment is responsible for saponifying the key bonds between lignin and carbohydrates, while the ammonia released from urea decomposition further penetrates and destroys the lignin structure. Under this synergistic effect, sugarcane leaves treated under optimal conditions (2.5% KOH + 1.5% urea, 80℃, 2h) showed a significant reduction in lignin content from 17.09% to 4.67% (removal rate approximately 84.12%), while maintaining a high cellulose retention rate of 88.92% (see Table 1). This demonstrates that the method of this invention achieves an excellent balance between efficiently breaking down biodegradation barriers and effectively retaining the core carbon source.

[0018] 2. Furthermore, because pretreatment fundamentally improves the biodegradability of materials (i.e., microorganisms can more easily access and utilize the materials), the composting process is comprehensively optimized. Specifically, the compost pile heats up faster and the high-temperature period lasts longer. The pretreated group (KU) enters the high-temperature period much earlier than the untreated control group (CK), and the peak temperature is higher (Figure 3a). At the same time, the maturation speed is significantly accelerated. The pretreated group only needs about 10 days of composting for the seed germination index (GI) to exceed the 80% maturation safety threshold. Its maturation cycle is shortened by about 50% compared with the control group (about 20 days) (Figure 4b), and the overall composting efficiency is greatly improved.

[0019] 3. This method not only accelerates the composting process as mentioned above, but also fundamentally optimizes the intrinsic quality of the final product. On the one hand, the product is more thoroughly decomposed, with a seed germination index (GI) as high as 107.5% (Figure 4b), completely eliminating phytotoxicity. On the other hand, the product's nutrient content is efficiently enriched: the total potassium (TK) content reaches 44.72 g / kg, an increase of approximately 63.7% compared to the control group; the total nitrogen (TN) content is also significantly higher (Figure 5b, d). This is due to the fact that the pretreatment, while directly introducing potassium, effectively reduces nitrogen loss by promoting the transformation of organic matter into more stable humus (with a continuously lower E4 / E6 ratio, Figure 4c), thus achieving a dual nutrient gain through potassium addition and nitrogen retention.

[0020] 4. The process of this invention creatively selects potassium hydroxide as the alkali source, enabling it to directly integrate essential potassium nutrients for plants into the product while performing pretreatment, thus avoiding the potential soil risks associated with using sodium hydroxide. Furthermore, the nitrogen- and potassium-rich filtrate produced during pretreatment can be reused as liquid fertilizer, forming a closed-loop nutrient cycle model of "pretreatment - solid fertilizer composting - liquid fertilizer recovery." This not only improves resource utilization efficiency but also reduces waste emissions, significantly enhancing the environmental and economic sustainability of the technology.

[0021] In summary, this invention reveals and utilizes the synergistic mechanism between potassium hydroxide and urea to develop a highly efficient and selective pretreatment method. This approach not only systematically overcomes the technical bottlenecks of slow degradation, long cycle, and low fertilizer efficiency in sugarcane leaf compost, but also achieves the green transformation from agricultural waste to high-quality agricultural products through in-situ nutrient addition and process resource recycling, providing an innovative resource utilization path that combines efficiency, value, and environmental benefits. Attached Figure Description

[0022] Figure 1 is a schematic diagram of the effect of pretreatment on the main components of sugarcane leaves. Figure 1a is a comparison of the contents of the main components (cellulose, hemicellulose, lignin) before and after pretreatment, and Figure 1b is a comparison of the degradation rate / retention rate of the corresponding components.

[0023] Figure 2 shows a comparison of the structural characterization and biodegradability of sugarcane leaves before and after pretreatment, where:

[0024] Figures 2a-2c show scanning electron microscope (SEM) images of untreated sugarcane leaves at different magnifications;

[0025] Figures 2d-2f are SEM images of sugarcane leaves after pretreatment with potassium hydroxide-urea according to the present invention at different magnifications.

[0026] Figure 2g is a comparison of the Fourier transform infrared (FTIR) spectra of sugarcane leaves before and after pretreatment;

[0027] Figure 2h shows a comparison of the X-ray diffraction (XRD) spectra of sugarcane leaves before and after pretreatment;

[0028] Figure 2i is a comparison of the degradation rate of sugarcane leaves before and after pretreatment during solid-state fermentation over time.

[0029] Figure 3 shows the curves of key physical parameters during the composting process, where Figure 3a shows the temperature change curve of the compost pile, Figure 3b shows the moisture content change curve of the material, and Figure 3c shows the pH value change curve of the material.

[0030] Figure 4 shows the curves of key indicators for evaluating compost maturity and stability. Figure 4a shows the curve of electrical conductivity (EC) of compost extract, Figure 4b shows the curve of seed germination index (GI), and Figure 4c shows the curve of E4 / E6 ratio of extract.

[0031] Figure 5 shows the nutrient content change curves of the materials during the composting process. Figure 5a shows the total organic carbon (TOC) content change curve, Figure 5b shows the total nitrogen (TN) content change curve, Figure 5c shows the carbon-nitrogen ratio (C / N) change curve, and Figure 5d shows the total potassium (TK) content change curve. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are specific implementations of a part of this invention, but not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0033] I. Materials and Methods

[0034] Unless otherwise stated, the experimental methods used in the embodiments of the present invention are all conventional methods, and the reagents and instruments used are all commercially available.

[0035] 1. Experimental materials:

[0036] (1) Agricultural waste: Sugarcane leaves, taken from Wuwei Sugar Factory in Nanning City, Guangxi Zhuang Autonomous Region. The raw material is air-dried and yellow in color. After being crushed by a multi-functional pulverizer and passed through a 40-60 mesh sieve, it is dried and sealed for later use. Its main dry basis components are: cellulose 36.29%, hemicellulose 25.59%, lignin 17.09%, carbon content 44.23%, and nitrogen content 1.06%.

[0037] (2) Auxiliary material: cow dung, taken from Zhuangniu Company, Chaoyang Street, Xingning District, Guangxi Zhuang Autonomous Region. Its carbon content is 40.95% and nitrogen content is 2.13%.

[0038] (3) Chemical reagents: Potassium hydroxide (KOH, analytical grade), purchased from Tianjin Damao Chemical Reagent Factory; urea (urea, analytical grade), purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0039] (4) Microbial inoculants: purchased from Xingyeyuan Microbial Co., Ltd., the main components of which are Bacillus subtilis, yeast and Bacillus licheniformis, used for solid-state fermentation experiments.

[0040] 2. Main Analytical Methods

[0041] (1) Component analysis: The cellulose, hemicellulose and lignin content of sugarcane leaves were determined according to the standard method of the National Renewable Energy Laboratory (NREL) of the United States.

[0042] (2) Structural characterization:

[0043] A. Fourier Transform Infrared Spectroscopy (FTIR): A Shimadzu IRTracer-100 spectrometer was used. The sample was mixed with potassium bromide at a mass ratio of 1:100 and compressed into a pellet. The spectroscopy was performed at 4000-500 cm⁻¹. -1 Scan within the range.

[0044] BX-ray diffraction (XRD): A Rigaku SmartLab diffractometer was used, with a scanning range of 2θ of 5°–60° and a scanning speed of 2° / min. Crystallinity (CrI) was calculated using the following formula:

[0045] (1)

[0046] Among them, I 002 I represents the diffraction peak intensity of the cellulose (002) crystal plane at 2θ = 22.4°. am The intensity of the diffraction peak in the amorphous region at 2θ = 18.2° is given.

[0047] (3) Solid-state fermentation degradation rate: Calculated using the following formula to evaluate the pretreatment effect:

[0048] (2)

[0049] (4) Analysis of compost properties

[0050] Mix the compost sample with deionized water at a ratio of 1:10, place it in a shaker at 200 r / min for 1 hour, and centrifuge the resulting liquid at 10000 rpm for 10 min. The resulting supernatant is the compost extract.

[0051] The pH and electrical conductivity (EC) of the compost extract were measured using a digital pH meter (FE28, Mettler, China) and an electrical conductivity meter (FE38, Mettler, China), respectively. The germination index (GI), a key indicator for assessing compost maturity and phytotoxicity, was determined according to the method described in the Chinese agricultural industry standard NY / T 525-2021.

[0052] The degree of humification was characterized by the E4 / E6 ratio, which was calculated by measuring the absorbance of the extract at 465 nm and 665 nm using a UV-Vis spectrophotometer (8453 series, Agilent, USA). The nutrient content in the compost powder samples included total organic carbon (TOC), total nitrogen (TN), and total potassium (TK), all determined according to the corresponding Chinese standards: TOC was analyzed according to NY / T 4606-2025, total nitrogen was determined according to NY / T 2542-2014, and total potassium was determined according to NY / T2540-2014.

[0053] II. Implementation Examples

[0054] Example 1:

[0055] This embodiment discloses a combined pretreatment method of potassium hydroxide and urea for improving composting efficiency, demonstrating the complete implementation process and effects of the technical solution of the present invention under optimal conditions. It includes the following steps:

[0056] (1) Raw material pretreatment: Prepare 200 mL of pretreatment solution, in which the mass concentration of KOH is 2.5% and the mass concentration of urea is 1.5%. Mix 20 g of sugarcane leaves that have passed through a 40-mesh sieve with the pretreatment solution and heat in an oil bath at 80℃ for 2 hours. After the reaction is complete, filter with a 150-mesh filter bag, wash the solid residue with deionized water until neutral, and dry at 105℃ to obtain pretreated sugarcane leaves for relevant pretreatment characterization.

[0057] (2) Characterization of pretreatment effect:

[0058] 1) Component changes: NREL analysis showed that the lignin content of sugarcane leaves decreased significantly from 17.09% to 4.67% after pretreatment, while the cellulose content increased from 36.29% to 55.49% (see Figures 1a and 1b).

[0059] 2) Structural changes: SEM images (Fig. 2a-f) show that the surface of sugarcane leaves changed from smooth and dense to rough and porous after pretreatment, with a large number of cracks.

[0060] 3) Functional groups and crystallinity: Characteristic peaks representing lignin in the FTIR spectrum (Figure 2g) (e.g., 1743 cm⁻¹) -1 1510cm-1 The intensity was significantly reduced. XRD analysis (Figure 2h) showed that the cellulose type I crystal structure was retained, but the relative crystallinity decreased from 50.06% to 37.38%, indicating that amorphous elements were preferentially removed.

[0061] (3) Solid-state fermentation verification: The pretreated sugarcane leaves were subjected to solid-state fermentation (sterilized at 121℃ for 20 minutes, inoculated with 2×10 6 (A composite bacterial culture of CFU / mL was incubated at 37℃). As shown in Figure 2i, after 15 days of fermentation, the degradation rate of the pretreated group reached 18.64%, which was much higher than the 7.02% of the untreated group.

[0062] (4) Composting Experiment and Evaluation: Pretreated sugarcane leaves and cow manure were mixed by dry weight, and the initial C / N ratio was adjusted to 25:1 with a moisture content of 65%. Aerobic composting was carried out in a 45L polystyrene container, with regular turning. During the composting process, the pretreated group (KU) heated up faster and had a higher peak temperature (Fig. 3a), and the moisture content decreased more rapidly (Fig. 3b). Finally, the germination index (GI) of the KU compost product reached 107.5% (Fig. 4b), and the E4 / E6 ratio was lower (Fig. 4c). At the same time, the TOC content of the KU group was consistently lower than that of the CK group during the composting process (Fig. 5a), indicating that the organic matter degradation was more thorough; its total nitrogen (TN) and total potassium (TK) content were significantly higher than those of the CK group (Fig. 5b, d), and the carbon-nitrogen ratio (C / N) decreased to a lower level (Fig. 5c). The above results indicate that the pretreated material has higher maturity and better fertilizer efficiency.

[0063] Example 2:

[0064] This embodiment verifies the feasibility of the lower limit of the parameter range in the claims (1.5% KOH, 1.0% urea, 60℃, 0.5 hours). Except for the change in pretreatment conditions, the remaining steps are the same as in Example 1. Under these mild conditions, the pretreatment still has a significant destructive effect on the lignocellulose structure of sugarcane leaves. The treated material, when composted (with the initial C / N ratio adjusted to 20:1), showed a slightly slower rate of temperature rise and a significantly higher peak temperature compared to Example 1, but was still significantly better than the untreated control group (Control Example 1). It also completed composting within a reasonable period, and the final product had a seed germination index (GI) greater than 80%, meeting the standards for safe application. These results indicate that this parameter combination represents the minimum feasible condition for the effectiveness of the technical solution of this invention.

[0065] Example 3:

[0066] This embodiment verifies the feasibility of the upper limit of the parameter range in the claims (4.0% KOH, 3.0% urea, 95℃, 4 hours). Except for the change in pretreatment conditions, the remaining steps are the same as in Example 1. Under these conditions, the pretreatment removes lignin more thoroughly, and due to the higher alkali concentration, more potassium is introduced. The treated material was used for composting (adjusting the initial C / N ratio to 30:1), and the composting process exhibited characteristics of vigorous initial reaction and rapid organic matter degradation. The total potassium content of the final compost product was significantly higher than that of Example 1, making it particularly suitable for preparing high-potassium organic fertilizers or soil conditioners with specific potassium requirements. This parameter combination demonstrates the flexibility of this invention in adapting to different product positioning needs by adjusting the pretreatment intensity.

[0067] III. Comparison Example

[0068] To illustrate the effectiveness of this application, the applicant conducted a comparative experiment:

[0069] CK group: Untreated control group.

[0070] This comparative example aims to demonstrate the inherent defects of sugarcane leaf compost without pretreatment.

[0071] Method: Sugarcane leaves were directly mixed with cow manure at an initial C / N ratio of 25:1 and a moisture content of 65% without any chemical pretreatment, and then composted aerobically. This group was designated as the CK group.

[0072] Results and Analysis: Composting process monitoring showed (see Figure 3a) that the CK group compost pile heated up slowly, reaching a significantly lower maximum temperature than the pretreated group (KU group), and the high-temperature period was shorter. This indicates that the dense lignocellulose structure of untreated sugarcane leaves severely limited the initial activity and degradation efficiency of microorganisms. Ultimately (day 31), the seed germination index (GI) of the CK group compost product was 93.65% (see Figure 4b), and the total nitrogen (TN) and total potassium (TK) contents were also significantly lower than those of the KU group (see Figures 5b, 5d). These results directly confirm the necessity of pretreatment technology.

[0073] Next, to further explore the differences in the core effects of different pretreatment methods, the applicant also focused on examining the impact of each method on the lignin removal efficiency of sugarcane leaves, grouped as follows:

[0074] Comparative Example 1: Only 2.5% KOH treatment was performed, and other treatment steps were the same as in Example 1.

[0075] Comparative Example 2: Only 1.5% urea was used for treatment, and other treatment steps were the same as in Example 1.

[0076] Comparative Example 3: 2.5% NaOH + 1.5% urea, with other treatment steps the same as in Example 1.

[0077] Comparative Example 4: 5.0% KOH + 0.5% urea (high alkalinity, low nitrogen), with other treatment steps the same as in Example 1.

[0078] The key data for each group are compared in the table below.

[0079] Table 1. Comparison of the effects of different pretreatment methods on the lignin content of sugarcane leaves

[0080]

[0081] In the table, lignin removal rate (%) = [(raw material lignin content - treated lignin content) / raw material lignin content] × 100%; cellulose retention rate (%) = (treated cellulose content / raw material cellulose content) × 100%. A retention rate exceeding 100% indicates that cellulose is relatively enriched due to the removal of components such as lignin.

[0082] As shown in Table 1, the synergistic pretreatment scheme of the present invention (Example 1) achieves an excellent balance in selectively breaking down the lignocellulose structure. Its lignin removal rate reaches 84.12%, while the cellulose retention rate remains at 88.92%, indicating that this scheme can efficiently destroy the main barrier to microbial degradation (lignin) and maintain the carbon source framework and physical structure (cellulose) of the compost material to the greatest extent possible.

[0083] Through system comparison, the advantages of this invention are specifically manifested in the following aspects:

[0084] (1) Compared with single-component treatment: Although Control Example 1 (KOH only) has considerable delignification ability (80.23%) and cellulose retention rate (90.7%), it lacks urea synergy, and its mechanism of action is singular, which may not be sufficient to destroy stubborn bonds (such as phenyl ether bonds) in lignin; Control Example 2 (urea only) has a mild effect and limited pretreatment effect (removal rate of only 24.52%). This proves that the combination of KOH and urea is necessary to achieve efficient pretreatment, and neither can be omitted.

[0085] (2) Compared with different alkali sources: Control Example 3 (NaOH substitution) achieved a slightly higher delignification rate (85.56%), but its cellulose retention rate (82.48%) was significantly lower than that of the present invention (88.92%). This indicates that the use of KOH instead of NaOH is one of the key factors that enables the present invention to achieve efficient delignification while retaining cellulose to a higher degree. In addition, KOH also introduces potassium nutrients that are essential for plants.

[0086] (3) Compared with extreme process parameters: Comparative Example 4 (high alkali and low nitrogen) achieved an extremely high delignination rate (94.69%) by doubling the alkali content, but this came at the cost of severe cellulose loss (the retention rate dropped sharply to 59.73%), resulting in poor economic efficiency and sustainability. This, in turn, confirms the scientific nature and optimization value of the specific ratio (2.5% KOH + 1.5% urea) of this invention.

[0087] Comprehensive comparative analysis shows that the synergistic pretreatment scheme of this invention is not a simple improvement on existing technologies. It achieves an optimal balance between the often contradictory goals of efficient lignin removal and high cellulose retention. This balance is significantly better than single-reagent treatments and alternative solutions that change the alkali source or alter the ratio, fully demonstrating the unique synergistic advantages of potassium hydroxide and urea under the specific ratio and process of this invention.

[0088] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for combined pretreatment with potassium hydroxide and urea to improve composting efficiency, characterized in that, Includes the following steps: The agricultural waste is mixed with a pretreatment solution and then heated; wherein the pretreatment solution is a mixed aqueous solution containing both potassium hydroxide and urea.

2. The method according to claim 1, characterized in that, The agricultural waste is sugarcane leaves. In the pretreatment solution, the mass concentration of potassium hydroxide is 1.5%-4.0%, the mass concentration of urea is 1.0%-3.0%, the heating temperature is 60-95℃, and the treatment time is 0.5-4 hours.

3. The method according to claim 1, characterized in that, The pretreatment solution contains 2.5% potassium hydroxide and 1.5% urea by mass, and the heating temperature is 80°C for 2 hours.

4. A method for preparing well-rotted organic fertilizer, characterized in that, Includes the following steps: S1: Sugarcane leaves are treated using the pretreatment method described in any one of claims 1-3 to obtain pretreatment residue; S2: Mix the pretreated residue with livestock and poultry manure, adjust the initial carbon-nitrogen ratio to 20-30:1, and carry out aerobic composting.

5. The method according to claim 4, characterized in that, The livestock and poultry manure is cow manure, the initial carbon-to-nitrogen ratio is 25:1, and the initial moisture content of the compost material is 60%-70%.

6. An organic fertilizer, characterized in that, Prepared by the method described in any one of claims 4-5.

7. Application of the combination of potassium hydroxide and urea as a pretreatment agent for sugarcane leaf composting.

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