A modified biochar and a preparation method and application thereof

Abstract

The application discloses modified biochar as well as a preparation method and application thereof, and belongs to the technical field of aerobic compost additives, and the preparation method of the modified biochar comprises the following steps: corn straw biochar is added into a Na2HPO4 solution according to a solid-liquid ratio of 1g:5-10mL by using an impregnation method, an alkaline solution is used to adjust the pH of the mixed system to 10.8-11.2, then magnetic stirring reaction is carried out, after the reaction is completed, centrifugal separation, washing and drying are carried out, and the modified biochar is obtained. The modified biochar prepared in the application can significantly reduce greenhouse gas emission, improve nitrogen retention and compost nutrient content, promote compost maturity and reduce phytotoxicity, and directionally regulate microbial community structure when the modified biochar is used as an aerobic compost additive. That is, the application enhances the functionality of the biochar through chemical modification, realizes the synergism of 'pollution reduction, efficiency increase, carbon fixation and compost promotion', and provides an effective technical path for realizing low-carbon, high-efficiency and sustainable organic waste resource utilization.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aerobic composting additives, and particularly relates to modified biochar as well as a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of animal husbandry, the scale of livestock and poultry breeding is expanding, and the amount of organic waste, especially manure, is increasing dramatically. Aerobic composting, as an effective technology for converting livestock and poultry manure into stable, harmless, and nutrient-rich organic fertilizer, has been widely used in the resource utilization of agricultural waste. However, traditional composting processes still face many challenges, especially in terms of composting efficiency, product quality, and environmental impact.

[0003] Firstly, incomplete or low maturity compost releases a large amount of low molecular weight organic acids (such as acetic acid, propionic acid, etc.) during microbial degradation, which are plant toxic and can inhibit seed germination and crop growth, severely affecting the agricultural value of the compost product. In addition, nitrogen loss is serious during the composting process, mainly in the form of ammonia (NH3) volatilization and nitrous oxide (N2O) emission, reducing the nutrient content of the fertilizer. CH4 and N2O, as strong greenhouse gases, have a much higher global warming potential (GWP) than CO2, with CH4 contributing up to 80% of the GWP 100 in composting, and N2O accounting for 50-90% of the GWP in nitrogen-rich waste composting. Therefore, while achieving resource utilization, traditional composting processes also become a source of greenhouse gas emissions that cannot be ignored, restricting their sustainable development.

[0004] To address the above problems, researchers have attempted to optimize the composting process by adding exogenous regulators in recent years. Among them, biochar is widely used as a compost additive due to its high specific surface area, rich pore structure, and oxygen-containing functional groups. It can reduce nitrogen loss by adsorbing NH3, NH4 + , and NO x , etc., and at the same time provide a habitat for microorganisms to promote organic matter degradation. Diatomite, as a natural porous siliceous material, also has high porosity, large specific surface area, and good water retention and air permeability, which can improve the structure of the compost and enhance microbial activity, and is also considered as a potential compost improver. However, although biochar and diatomite improve the quality of composting and reduce gas emissions to some extent, their mechanisms are still mainly dependent on physical adsorption and structural improvement, and their ability to direct regulate microbial communities is limited, and there are bottlenecks in long-term stability, nitrogen retention efficiency, and greenhouse gas emission reduction effect.

[0005] Furthermore, the existing researches mainly focus on the single application of raw biochar or diatomite, and lack of systematic research on different types of additives, especially the chemically modified biochar. In addition, the succession rules of the core microbial community in compost (such as Proteobacteria, Bacteroidetes, Actinobacteria, etc.) and the coupling relationship between the additives and CH4 and N2O emissions are still lack of in-depth molecular ecological analysis. This lack seriously limits the scientific selection and precise regulation of compost additives, and hinders the popularization and application of efficient, low-carbon and sustainable composting technology. SUMMARY

[0006] In view of the above technical problems, the present application provides a modified biochar and a preparation method and application thereof.

[0007] To achieve the above object, the present application provides the following technical scheme:

[0008] A preparation method of a modified biochar, comprising the following steps:

[0009] The corn straw biochar is added into a Na2HPO4 solution according to a solid-liquid ratio of 1g:5-10mL by using the impregnation method, an alkali solution is used to adjust the pH of the mixed system to 10.8-11.2, then magnetic stirring reaction is carried out, after the reaction is completed, centrifugal separation, washing and drying are carried out, and the modified biochar is obtained.

[0010] Optionally, the particle size of the corn straw biochar is 0.1-0.2mm; preferably 0.15mm.

[0011] Further, the preparation process of the corn straw biochar is as follows:

[0012] The corn straw powder is heated to 425-475℃ at a heating rate of 10℃ / min, and kept at this temperature for 2h to obtain the corn straw biochar.

[0013] Further, the particle size of the corn straw powder is 50-100mm.

[0014] Optionally, the solid-liquid ratio is 1g:10mL.

[0015] Optionally, the concentration of the Na2HPO4 solution is 0.56mol / L.

[0016] Optionally, the alkali solution is a sodium hydroxide solution with a concentration of 0.1mol / L.

[0017] Optionally, the pH of the mixed system is 11.

[0018] The application constructs a systematic and synergistically optimized modified biochar preparation system. First, the application adopts a specific temperature control pyrolysis process, i.e. pyrolyzing corn straw powder to 425-475℃ at a heating rate of 10℃ / min and keeping constant temperature for 2 hours, which effectively regulates the carbonization degree and pore structure development of biochar, and lays a good physical and chemical foundation for subsequent chemical modification. On this basis, surface chemical modification is carried out by using sodium hydrogen phosphate solution immersion method, and by accurately controlling the key parameters such as solid-liquid ratio (1g:10mL), Na2HPO4 concentration (0.56 mol / L) and system pH value (11.0), the modified biochar which can effectively reduce the cumulative emission of CH4, N2O and CO2 is successfully prepared. That is, the above series of parameters defined in the application are not selected independently, but are an optimized combination based on the systematic understanding of the physicochemical properties of biochar, surface chemical behavior and compost function requirements, and a high-efficiency, low-carbon and sustainable organic waste resourceization technical path is constructed.

[0019] Optionally, the magnetic stirring conditions are: magnetic stirring in a 50℃ constant temperature water bath for 6h.

[0020] A modified biochar prepared by the above preparation method.

[0021] A compost additive comprising the above modified biochar.

[0022] Application of the above modified biochar in the field of aerobic composting, wherein the addition amount of the modified biochar is 5wt.% of the fertilizer.

[0023] Compared with the prior art, the application has the following advantages and technical effects:

[0024] 1. Significant reduction of greenhouse gas emissions: compared with the control group and the original biochar and diatomite, the modified biochar prepared by the application can effectively reduce the cumulative emission of CH4, N2O and CO2, and has excellent greenhouse gas emission reduction capacity.

[0025] 2. Improvement of nitrogen retention and compost nutrient content: the modified biochar prepared by the application can significantly improve the total nitrogen (TN) and total organic carbon (TOC) in the compost product, which helps to reduce nitrogen loss and improve the value of the fertilizer.

[0026] 3. Promotion of compost maturity and reduction of phytotoxicity: the modified biochar prepared by the application can significantly improve the seed germination index (GI) by 27.4%, indicating that the compost maturity is high, the phytotoxicity is low, the product is safer and more suitable for agricultural use.

[0027] 4. Optimization of compost physicochemical properties: the modified biochar prepared by the application can increase the pH of the compost, reduce the electrical conductivity (EC), enhance the stability of the compost, and improve the quality of the final product.

[0028] 5. Directional regulation of microbial community structure: The modified biochar prepared by the present application can significantly enrich key functional flora with nitrogen fixation, organic matter degradation and environmental adaptation functions, such as Devosia (37%) and Mesorhizobium (8%), to promote beneficial microbial activities and strengthen the biological conversion process of compost.

[0029] 6. Improve the overall quality and sustainability of compost: The present application enhances the functionality of biochar through chemical modification, realizes the synergistic effect of "pollution reduction, efficiency increase, carbon fixation and decomposition promotion", and provides an effective technical path for realizing low-carbon, efficient and sustainable utilization of organic waste resources.

[0030] In summary, the Na2HPO4 modified biochar prepared by the present application is not only a high-efficiency compost additive, but also has important application value in promoting the development of green agriculture and circular economy. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application, and are incorporated in and constitute a part of this application. The illustrations, together with the description, serve to explain the application offered by the present application. In the drawings:

[0032] Figure 1 is a structure diagram of the aerobic composting system;

[0033] Figure 2 is the effect of different additives on key physicochemical and biological parameters in the composting process of cow dung; wherein A is temperature, B is pH value, C is electrical conductivity (EC), and D is germination index;

[0034] Figure 3 is a curve graph of the change of total organic carbon (TOC) (A) and total nitrogen (TN) (B) in the composting process under different treatments;

[0035] Figure 4 is a dynamic diagram of greenhouse gas emissions in the composting process under different treatments, wherein A and B are CH4 emission rate and cumulative CH4 emission, respectively; C and D are CO2 emission rate and cumulative CO2 emission, respectively; E and F are N2O emission rate and cumulative N2O emission rate, respectively;

[0036] Figure 5 is a graph of the composition of microbial community and principal component analysis under different composting treatments; wherein A is door, B is genus, C is the relative abundance of dominant taxa at the species level; D-F is a heat map of microbial changes under different composting treatments, and G is a PCA bivariate plot at the door level; H is a principal component analysis bivariate plot at the genus level;

[0037] Figure 6The images show the material characterization of different compost samples, where A is the XRD spectrum, B is the FTIR spectrum, and C is the SEM image.

[0038] Figure 7 This diagram illustrates the multivariate interactions between compost physicochemical parameters, greenhouse gas (GHG) emissions, and microbial community dynamics under different composting treatments. In this diagram, A represents the principal component analysis of greenhouse gas emissions with different treatment conditions, B represents the principal component analysis of greenhouse gas emissions with composting time, and C represents the correlation analysis of compost physicochemical parameters (indicators), greenhouse gases, and microorganisms. Detailed Implementation

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0040] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0041] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0042] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0043] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0044] Unless otherwise specified, the term "parts" in this invention refers to parts by weight.

[0045] All raw materials used in this invention were purchased from the market. The cow dung raw material came from Luxiang, Shuangyang District, Changchun City. After removing stones and other impurities, it was air-dried for later use. The diatomaceous earth used in the experiment was grade II diatomaceous earth powder, purchased from Diatomaceous Earth Functional Materials Co., Ltd. The corn stalks came from a farm in Changchun, China.

[0046] The technical solution of the present invention will be further illustrated by the following embodiments.

[0047] Example 1

[0048] A method for preparing modified biochar as a composting additive

[0049] Step 1: Preparation of Biochar

[0050] Corn stalks were crushed to a particle size of 50–100 mm and placed in a biogasifier (model: AT / SQ-2000) for pyrolysis. The heating rate was 10℃ / min, and the temperature was raised to 450±25℃ and kept at this temperature for 2 hours. After pyrolysis, the mixture was naturally cooled to room temperature to obtain corn stalk biochar. The obtained corn stalk biochar was ground and sieved to collect biochar particles with a particle size of 0.15 mm for later use.

[0051] Step 2: Modification by impregnation with disodium hydrogen phosphate (Na2HPO4) solution

[0052] Weigh 50 g of the corn stalk biochar and add it to 500 mL of 0.56 mol / L Na2HPO4 solution to fully submerge the biochar. Then, slowly adjust the pH of the mixture to 11.0 using 0.1 mol / L NaOH solution. Place the mixture in a 50℃ constant temperature water bath and react for 6 hours under magnetic stirring.

[0053] Step 3: Washing and Drying

[0054] After the reaction was completed, the modified biochar was centrifuged to collect the solid product; then it was washed repeatedly with distilled water 5 times and dried to constant weight to obtain Na2HPO4 modified corn straw biochar.

[0055] Example 2

[0056] The difference from Example 1 is that the solid-liquid ratio of corn straw biochar and Na2HPO4 solution is 1g:5mL, that is, 50g of corn straw biochar and 250mL of Na2HPO4 solution.

[0057] Example 3

[0058] The difference from Example 1 is that the solid-liquid ratio of corn straw biochar and Na2HPO4 solution is 1g:7mL, that is, 50g of corn straw biochar and 350mL of Na2HPO4 solution.

[0059] Example 4

[0060] The difference from Example 1 is that the pH of the mixture was slowly adjusted to 10.8 using a 0.1 mol / L NaOH solution.

[0061] Example 5

[0062] The difference from Example 1 is that the pH of the mixture was slowly adjusted to 11.2 using a 0.1 mol / L NaOH solution.

[0063] Comparative Example 1

[0064] Diatomaceous earth is used as a composting additive.

[0065] Comparative Example 2

[0066] The corn straw biochar prepared in Example 1 was used as a composting additive.

[0067] Effect verification

[0068] An aerobic composting experiment was conducted for 45 days by adding 5% diatomaceous earth (Comparative Example 1), 5% corn straw biochar (Comparative Example 2), and 5% Na2HPO4 modified biochar (Example 1, based on dry weight) to cow manure compost. Four treatment groups were set up: control (CK), 5% diatomaceous earth (T1), 5% biochar (T2), and 5% Na2HPO4 modified biochar (T3).

[0069] like Figure 1 As shown, the aerobic composting system includes a compost mixer, an insulation layer, an air pump for forced aeration, a sieve plate to ensure airflow distribution, and a thermometer to monitor the internal temperature; compost leachate is collected at the base through a drain outlet, and gas is discharged through an exhaust outlet.

[0070] The specific composting process is as follows:

[0071] The mixture (cow manure + additives) was homogenized and composted in a 60 L reactor with an aeration rate of 0.6 L / min and an aeration cycle of 5 min on / 45 min off. Samples were collected at 13 time points over 45 days of composting, stored at -20˚C for basic analysis and at -80˚C for microbial identification.

[0072] 1. Methods for analyzing compost characteristics

[0073] After extraction with distilled water, the pH and EC of the compost were determined using an MP521 analyzer (Shanghai, China). Total nitrogen (TN) and total organic carbon (TOC) were determined by sulfuric acid-hydrogen peroxide digestion and potassium dichromate oxidation, respectively. Greenhouse gases (CH4, CO2, and N2O) were analyzed periodically using chromatography. Surface morphology was characterized using a Hitachi S-4100 scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The samples were coated with 50 nm chromium (LEICA ACE 660) and imaged under high vacuum (15-20 kV, 100 pA) using BSE and SE modes to distinguish composition and topographic features. Elemental composition was determined using energy dispersive spectroscopy (EDS) with a 30 mm aperture. 2 Bruker detector and Quantax Esprit 1.9 software. Analysis of 600–4000 cm⁻¹ spectra was performed using ATR-FTIR spectroscopy (PerkinElmer Spotlight 100). -1 Functional groups within the range, with a resolution of 4 cm. -1 On average, each sample was scanned four times. Data were processed using Spectrum V6 software. XRD (RIGAKU D / MAX 2550 / PC, Cu KR radiation, 40kV / 40mA) was used, with a scan range of 10 and a scanning range of I (20, 0.026I step size), in accordance with JCPDS PDF-22004 standard.

[0074] 2. Microbial community analysis

[0075] Genomic DNA was extracted using the OMEGA DNA Kit (M5635-02) and stored at -20˚C. DNA quantity and quality were assessed by NanoDropNC2000 and agarose gel electrophoresis. The V3-V4 region of the bacterial 16S rRNA gene was amplified using primers 338F and 806R, followed by sample-specific 7bp barcoding. PCR was performed using Fast Pfu DNA Polymerase at 25 cycles of denaturation (98˚C, 30s), annealing (53˚C, 30s), and extension (72˚C, 45s). Amplicons were purified using Vazyme DNA Clean Beads, quantified using the Quan-it PicoGreen dsDNA Assay Kit, and summarized and sequenced on the Illumina MiSeq platform (MiSeq Reagent Kit v3) at Shanghai Personal Biotechnology Co., Ltd.

[0076] 3. Seed germination experiment

[0077] The compost sample was mixed with deionized water at a solid-liquid ratio (mass / volume) of 1 g:10 ml and shaken at 150 rpm for 1 hour in a temperature-controlled shaker. After centrifugation at 5000 rpm for 10 minutes, the supernatant was filtered through a qualitative filter. Subsequently, 5 mL of the filtrate was added to qualitative paper in a petri dish, and 15 corn seeds were evenly distributed on the paper. The petri dish was incubated at 25°C and 50% humidity for 48 hours.

[0078]

[0079] 4. Statistical Analysis

[0080] Statistical analysis was performed using StatisticX 8.1 software. One-way ANOVA with a p < 0.05 significance level was used to process and separate the large dataset. Graphs were created using OriginLab 2024b. Sequence data were processed in QIIME2, and ASV richness was estimated based on the ASV table. Microbial community structure was visualized using OriginLab and generated using GenesCloud V1.1 (Shanghai Personal Biotechnology Co., Ltd, China).

[0081] Results and Discussion

[0082] 1. Changes in physicochemical properties during composting

[0083] Figure 2 The effects of different additives on key physicochemical and biological parameters during cow manure composting are shown in Figure 1. A represents temperature distribution, B represents pH dynamics, C represents electrical conductivity (EC), and D represents the germination index (%). All results represent the mean ± standard deviation of three independent replicates.

[0084] Temperature is a key indicator of composting efficiency, reflecting the progress of microbial activity and processes. Composting typically involves four stages: aerobic, thermophilic, cooling, and maturation. Figure 2As shown in Figure A, all treatments, including diatomaceous earth (T1), raw biochar (T2), modified biochar (T3), and the control (CK), entered the thermophilic phase within the first 10 days. T2 (highest temperature 66.2°C, day 5) had the highest temperature, followed by T3 (highest temperature 65.2°C, day 6), T1 (highest temperature 62.5°C, day 8), and CK (highest temperature 60.2°C, day 9). Compared to the control, the temperatures of treatments T2, T3, and T1 increased by 11.7%, 7.4%, and 5.6%, respectively. All treatments maintained high-temperature conditions (>55°C) for more than 5 days, meeting the standards for harmless manure (GB7959) and ensuring pathogen inactivation. The temperature increase was closely related to the increase in microbial biomass and metabolic activity. Biochar significantly promoted this effect by enhancing aeration, reducing compost density, and through its porous structure and stable carbon content. Furthermore, the biochar-immobilized microbial community further accelerated the degradation of organic matter, enhanced thermophilic conditions, and promoted compost maturation. After 45 days, the temperature of all treatments dropped to ambient temperature, indicating that the compost had stabilized and matured.

[0085] pH value is an important indicator for measuring compost maturity and the biodegradation of organic matter. For example... Figure 2 As shown in Figure B, due to the alkalinity of diatomaceous earth and biochar, the pH of all improved treatment groups showed an upward trend in the early stages of composting, gradually exceeding that of the control (CK). After day 10, the pH decreased, likely driven by organic acids produced during microbial nitrification and decomposition. Subsequently, the pH rose until day 25, reflecting the degradation of organic acids, ammonification, and the conversion of organic nitrogen to ammonium. The peak pH values ​​during the stabilization period (40 days) were 8.5 (CK and T1), 8.6 (T2), and 8.5 (T3), mainly due to the accumulation of ammonia and the decomposition of organic acids. By day 45, the pH of all treatments stabilized between 8.0 and 8.6, meeting the requirements for mature compost in the organic fertilizer standard (NY / T 525-2012).

[0086] Electrical conductivity (EC) significantly affects the salinity, maturity, phytotoxicity, and plant growth of compost. Figure 2 The final EC values ​​shown by the C-cell curve were 3.21 (CK), 2.84 (T1), 2.69 (T2), and 2.86 mS / cm. -1 (T3). Initially, EC increased rapidly due to the concentration effect caused by the release of inorganic matter during organic decomposition and the reduction in compost volume. The subsequent decrease in EC was driven by NH3 volatilization and inorganic salt precipitation. Biochar modification significantly reduced compost EC by adsorbing ions and decreasing soluble salt concentration. All final EC values ​​were below 4.0 mS cm⁻¹. -1 The results meet the required standards, indicating that the plant is suitable for growth.

[0087] The germination index (GI) is used to evaluate the maturity and phytotoxicity of compost. For example... Figure 2 As shown in Figure D, the GI value gradually increased from day 0 to day 42, reaching 36.09% (CK), 102.60% (T1), 109.46% (T2), and 122.48% (T3), respectively, indicating that all improvement treatments had matured. GI was positively correlated with compost detoxification and quality. Biochar and diatomaceous earth effectively adsorbed toxic compounds, enhancing the detoxification and humification effects of compost, thus significantly increasing the GI. The GI values ​​of all treatment groups exceeded the compost maturity threshold (>70%, NY / T 525-2021), proving that they are non-toxic and suitable for agricultural use.

[0088] Figure 3 The graph shows the changes in total organic carbon (TOC) (A) and total nitrogen (TN) (B) during composting under different treatments.

[0089] like Figure 3 As shown in Figure A, the total organic carbon (TOC) gradually decreased until it stabilized, reflecting the rapid degradation of carbon by microbial activity. The final TOC values ​​were 44.38% (CK), 43.14% (T1), 42.10% (T2), and 43.29% (T3), respectively. The decrease in TOC observed during the thermophilic phase was mainly due to the microorganisms metabolizing carbon-rich materials into CO2. The addition of diatomaceous earth (T1) and biochar (T2) enhanced the porosity and aeration of the compost, significantly accelerating TOC degradation, consistent with changes in temperature and pH. Initially, T2 exhibited the highest TOC (56.89%) due to the inherently high carbon content of biochar.

[0090] The quality and agronomic value of compost depend largely on nitrogen concentration. Figure 3 As shown in Figure B, treatment T2 significantly increased the total nitrogen (TN) content at maturity (18.56%), compared to CK (16.72%), T1 (17.41%), and T3 (17.95%) (p < 0.05). Under high temperature and alkaline conditions, due to NH4+... + Due to the volatilization of NH3 and the rapid degradation of organic matter, total nitrogen (TN) initially decreased within the first nine days. The subsequent increase in TN was primarily due to the extensive decomposition of organic matter, which reduced compost quality and nitrogen concentration through a "concentration effect." The addition of diatomaceous earth and biochar (both primary and modified) with their high porosity and large surface area enhanced nitrogen retention by promoting the growth of nitrifying bacteria. The structure and active functional groups of biochar also limited organic nitrogen mineralization and promoted NH4+ evaporation. + The polymerization and nitrification processes enhance the nutritional value of compost. Modified biochar, due to its enhanced buffering capacity, further improves nitrogen retention, supporting the efficient conversion of organic nitrogen into NH4.+ .

[0091] 2. Greenhouse gas emission dynamics during aerobic composting

[0092] Figure 4 Greenhouse gas emission dynamics during composting under different treatments: A and B represent CH4 emission rates and cumulative CH4 emissions, respectively; C and D represent CO2 emission rates and cumulative CO2 emissions, respectively; E and F represent N2O emission rates and cumulative N2O emission rates, respectively. Compared with the control (CK), all modified treatments (T1-T3) significantly reduced CH4, CO2, and N2O emissions, with T3 (modified biochar) showing the most significant mitigation effect.

[0093] from Figure 4 As can be seen from Figure A, CH4 emissions peaked in the first week of composting, with the highest level observed in the control group (CK) (7.60 mg / kg). -1 ), followed by T1 (5.89 mg kg) -1 T2 (5.81 mg kg) -1 T3 (5.69 mg kg) -1 Emissions subsequently decreased over time due to reduced temperature and degradable carbon content. Compared to the control, CH4 emissions were cumulatively reduced by 40.18% (T3), 38.06% (T2), and 18.07% (T1). Modified biochar mitigated CH4 emissions by improving aeration, reducing bulk density, and enhancing the activity of methane-oxidizing bacteria. Corn straw biochar, with a lower activated carbon content than manure and diatomaceous earth additions, may be more effective as a composting bulking agent, as activated carbon can increase CH4 emissions. Biochar reduces CH4 emissions by adsorbing activated carbon and CH4 during composting. Corn straw biochar reduced activated carbon utilization, inhibited methane formation, enhanced methane oxidation, and resulted in lower CH4 emissions compared to diatomaceous earth addition and the control treatment. After approximately 15 days, reduced oxygen use slowed organic matter decomposition, promoted compost stabilization, and significantly reduced CH4 emissions. Figure 4 As can be seen from Figure C, CO2 emissions initially increased rapidly, followed by a second increase and then a decrease in all treatments. The peak emissions in the early stages of composting for T1, T2, and T3 were 16.37, 18.94, and 15.89 g kg, respectively. -1 VS d -1 The CK value was 19.29 g / kg. -1 VS d -1CO2 emissions are closely related to microbial activity and temperature. Modified biochar, due to its high porosity and surface area, enhances microbial metabolism by improving oxygen diffusion. Na2HPO4 modified biochar (T3) significantly reduced CO2 emissions by introducing alkali-active sites that enhance chemisorption. Overall, compared to the control, cumulative CO2 emissions were reduced by 17.07% (T1), 10.68% (T2), and 18.52% (T3). Figure 4 (As shown in D). These reductions are attributed to the improved pore structure, diatomaceous earth retaining moisture and supporting microbial activity, and biochar enhancing carbon dioxide adsorption and organic matter stabilization.

[0094] from Figure 4 As can be seen from E, N2O emissions showed a trend of first increasing and then decreasing in all treatments, compared with CK (2.43 mg kg). -1 Compared to treatment T3 (1.27 mg kg), -1 T2 (1.89 mg kg) -1 ) and T1 (2.30 mg kg) -1 The treatment significantly reduced peak emissions. Cumulative N2O emissions were reduced by 52.12% (T3), 44.28% (T2), and 35.46% (T1) compared to the control. The increase / decrease in emissions from biochar and diatomaceous earth treatments are attributed to their high porosity and surface area, which promoted aeration and slowed down nitrification and denitrification processes. Peak N2O release at 7–11 days was compared with NO3. - The increased N₂O concentration correlated with active nitrification and denitrification, although typical thermophilic conditions are considered unfavorable for these microorganisms. Modified biochar (T3) exhibited the highest N₂O reduction rate (71.28%), followed by diatomaceous earth (T1, 68.36%) and virgin biochar (T2, 65.36%). Modified biochar enhanced the microbial reduction process and adsorbed NH₃ / NH₄⁺. + Limiting nitrogen substrate availability and increasing oxygen availability inhibits denitrifying enzymes, thereby promoting N2O mitigation. Furthermore, the aromatization and alkalinity of biochar further reduce N2O emissions by increasing compost pH and inhibiting microbial N2O production.

[0095] 3. Microbial community structure

[0096] Figure 5 The microbial community composition and principal component analysis under different composting treatments are shown. Among them, A represents the phylum, B represents the genus, and C represents the relative abundance of dominant taxa at the species level. DF is a heatmap of microbial changes in different treatments (CK, T1, T2, T3), G is a PCA biplot at the phylum level, and H is a principal component analysis biplot at the genus level.

[0097] Phylum-level bacterial community analysis (e.g.) Figure 5 In study A), Proteobacteria (27-28%), Bacteroidota (19-23%), Acidobacteriota (10-12%), Chloroflexi (8-10%), and plananctomycetota (3-4%) were found to be the dominant groups, consistent with their roles in cellulose decomposition and nitrogen cycling. Proteobacterial abundance remained stable throughout the treatment, which was associated with reduced N2O emissions and enhanced nitrogen retention. Biochar (T2) significantly increased Bacteroidetes (17%) and promoted organic nitrogen mineralization, while diatomite (T1) enriched Firmicutes (62.68%) and Chlorofluorobacteria (19.86%), promoting aerobic decomposition and inhibiting pathogens by improving compost porosity. Compared to the control, Plananctomycetota abundance was significantly reduced in T1 (32.68%), T2 (26.38%), and T3 (17.86%). In treatment T3, desulfurizing bacteria and nitrosospirochetes were significantly reduced by 28.97% and 33.10%, respectively. The abundance of verrucomicrobiota also decreased by 15.93% (T1) and 11.70% (T2), respectively. Actinomycetes are important for degrading recalcitrant organic matter and promoting humification; compared with CK and T2, actinomycetes significantly increased in T1 (19.08%) and T3 (13.61%), likely driven by increased composting temperature and their ability to form stress-resistant spores. Biochar (T2) significantly increased the abundance of cyanobacteria (38.82%) and slime molds (44.89%), thereby promoting nutrient cycling, suppressing pathogens, and slowing CO2 release. Similarly, the enrichment of Verrucomicrobiota in T3 (33.60%) supported carbon turnover and compost stability. Biochar in T2 increased the abundance of desulfurizing bacteria (25.92%), while diatomaceous earth (T1) increased the abundance of nitrosospirochetes (21.37%). Both affected the nitrogen cycle and indirectly regulated CO2 emissions.

[0098] At the genus level (e.g.) Figure 5As shown in Figure B), the relative abundance of *Altererythrobacter* (12-17%) significantly increased in all treatments at T2. Compared to the control, *Devosia* (26-37%) was significantly enriched at T3, while its abundance decreased at T1 and T2. *Luteimonas* (9-15%) significantly increased at T2, while *Lysobacter* (4-6%) showed no significant difference between treatments. Compared to the control, the abundance of *Mesorhizobium* (5-8%) remained essentially unchanged, but increased slightly at T3 (8%). Conversely, compared to the control, *Hygrophytes* (6-11%) significantly decreased in all treatments. *Pseudomonas* (3-5%) and *Coleoptile* (4-5%) showed no significant change between treatments. *Streptomyces* significantly enriched at T2 (4-11%), while *Woeseia* (7-11%) was significantly less abundant than the control. Functionally, *Lactobacillus* plays multiple roles in nitric oxide reduction, denitrification, and carbon oxidation, particularly in mature compost. *Altererythrobacter*, *Devosia*, and *Streptomyces* become abundant during the composting maturation stage, promoting the turnover of refractory carbon compounds and playing a crucial role in nitrite ammoniation. Furthermore, *Mesrhizobium* and *Pseudomonas* are dominant genera involved in aerobic ammoniation, denitrification, and dissimilatory and assimilatory nitrate reduction processes, highlighting their key role in the nitrogen cycle during composting.

[0099] Figure 5 Heatmaps D, E, and F illustrate the changes in microbial community composition at the phylum, genus, and species levels across different composting treatments (CK, T1, T2, and T3). At the phylum level, Proteobacteria showed the most significant enrichment in T2, reflecting a high responsiveness to biochar, while *Plantomycetota* showed dominant abundance in the control (CK). At the genus level, *Rhizobium* was significantly enriched in T3, indicating enhanced ammonification activity, while *Pseudomonas* was enriched in T2, consistent with its known role in nitrate reduction. Species-level analysis showed that denitrifying *Pseudomonas* dominated in treatments T2 and T1, suggesting their involvement in the denitrification pathway. Furthermore, methanogenic species, such as *Methylcoccus marineensis* and methyl microbes, were consistently identified in all treatments, highlighting their roles in methane oxidation, heat tolerance, and improved biofiltration efficiency. In conclusion, the addition of additives during composting significantly remodels the structure and function of the microbial community, promoting a significant enrichment of microbial taxa involved in nitrogen transformation and methane oxidation.

[0100] Principal component analysis (PCA) clearly demonstrated the impact of compost additives on the microbial community composition. At the phylum level (e.g., ... Figure 5As shown in G), each modification produces a specific microbial assemblage: diatomaceous earth (T1) significantly enriches Firmicutes and Chlorophyta, while biochar (T2) favors Cyanobacteria and Desulfurizing Bacteria. The modified biochar treatment (T3) has the most significant effect, significantly enhancing Actinobacteria and Proteobacteria, which are crucial for nitrogen cycling. At the genus level (e.g., Figure 5 The modified biochar (T3) significantly increased the relative abundance of Devossia and Mesorhizobium, which is beneficial for nitrogen fixation and compost maturation. Biochar (T2) strongly enriched Streptomyces and Xanthomonas, both genera recognized for their role in degrading organic matter. Overall, these microbial changes support improved compost maturity and quality, as well as a significant reduction in greenhouse gas emissions achieved through treatment.

[0101] Figure 6 In the diagram, A represents the XRD patterns of compost samples CK, T1, T2, and T3; B represents the FTIR analysis; and C represents the SEM image.

[0102] from Figure 6 As can be seen in Figure A, the peaks at 26.5°, 28.2°, 29.3°, and 39.3° in the control group (CK) correspond to quartz, calcite, and potential phosphate or potassium salt phases, typically associated with raw cow manure compost. The enhanced peak observed at 26.5° in T1 confirms the incorporation of silicon-rich diatomite, attributed to its crystalline SiO2 structure. Conversely, the decreased peak intensities at 26.5°, 28.2°, and 29.3° in treatment groups T2 and T3 indicate increased amorphous content due to biochar. Furthermore, the novel peaks at 23.62° (T1), 27.72° (T2), and 23.49° (T3) may represent surface modification and the formation of new mineral phases, such as hydrated silicates, carbonates, or sodium phosphate compounds, resulting from the interaction of the modifier with the compost. However, the fundamental structural characteristics of the cow manure compost remained consistent across all treatments.

[0103] FTIR analysis (e.g.) Figure 6 Figure B shows the main functional groups responsible for chemical transformation in compost samples CK, T1, T2, and T3. 3400 cm -1 The nearby broadband corresponds to the OH stretching vibrations of hydroxyl groups, alcohols, phenols, and organic acids. 2920 ~ 2850 cm⁻¹ -1 and 2350 cm -1 The peaks at these locations represent the aliphatic C-H and O=C=O stretching vibrations of CO2, respectively. (1640~1651 cm⁻¹) -1 The wavelength range is caused by the skeletal vibrations of aromatic C=C, amides (amide I), quinones, or C=O stretching of H-bonded conjugated ketones. 1540–1410 cm⁻¹ -1The band reflects the asymmetric stretching of carbon and oxygen, the deformation of the carboxyl group (OH), and the NH bending vibration of the amide group. 1356 cm⁻¹ -1 and 1076 cm -1 The additional bands indicate S=O stretching vibrations, which are characteristic of sulfonamides and sulfoxide-like compounds.

[0104] The surface morphology of the compost material was characterized using SEM (e.g., ...). Figure 6 The study revealed significant differences between the treatments. The control (CK) exhibited a dense amorphous structure with limited porosity. In contrast, T1 maintained the typical porous structure of diatomaceous earth, while T2 and T3 displayed a distinct honeycomb morphology with surface stratification, significant etching, and increased pore complexity. These changes indicate substantial physicochemical transformations during composting, enhancing microbial colonization potential. The observed morphological changes highlight the important role of modified biochar in enhancing aeration, stimulating microbial activity, and improving overall compost quality. Furthermore, the biochar-related mineral structures detected by scanning electron microscopy suggest improved nutrient availability and compost maturity, which may be related to increased pH.

[0105] 4. Principal component analysis (PCA) and correlation analysis revealed the key drivers of composting performance.

[0106] Figure 7 This diagram illustrates the multivariate interactions between compost physicochemical parameters, greenhouse gas (GHG) emissions, and microbial community dynamics under different composting treatments. A represents principal component analysis (PCA) of greenhouse gas emissions versus different treatment conditions; B represents PCA of greenhouse gas emissions versus composting time; and C represents correlation analysis of compost physicochemical indicators, greenhouse gases, and microorganisms. CK (control group), T1 (diatomaceous earth compost), T2 (biochar compost), and T3 (modified biochar compost), with W1-W8 representing weeks 1 to 8, respectively. The first two principal components (PC1: 51.1%; PC2: 24.1%) together account for 75.2% of the total variance, demonstrating strong explanatory power. PCA of different treatment conditions and greenhouse gas emissions (e.g., ...) Figure 7 The analysis (shown in Figure A) illustrates the significant differences between different composting treatments. The control (CK) was closely correlated with CH4, CO2, and N2O carriers, indicating increased emissions and that compost maturity was not ideal. Conversely, the Na2HPO4 modified biochar treatment (T3) was positively correlated with total nitrogen (TN), germination index (GI), and higher pH, directly counteracting greenhouse gas carriers and highlighting its effectiveness in reducing emissions and improving compost quality. Diatomaceous earth (T1) and original biochar (T2) treatments were in the middle, indicating moderate improvement. Principal component analysis of composting time and greenhouse gas emissions (e.g., Figure 7Figure B further differentiated compost dynamics, identifying early clusters (1–3 weeks) associated with higher TOC, EC, and GHG emissions, transitioning to later clusters (7–8 weeks) characterized by increased GI and TN, reflecting compost stability. These temporal variations were closely correlated with observed microbial succession patterns, particularly the enrichment of nitrogen-transforming taxa such as Devosia and Mesorhizobium under T3 conditions. Overall, the PCA results highlight that Na2HPO4-modified biochar modifiers can reconstruct the physicochemical conditions and microbial communities of compost, promoting compost maturation and reducing environmental impact.

[0107] To further explore the relationship between physicochemical properties, greenhouse gas (GHG) emissions, and microbial communities, correlation analyses were conducted on various physicochemical indicators, greenhouse gases, and microbial communities (e.g., Figure 7 (As shown in C). Statistically significant correlations highlight the complex microbial-chemical interactions that drive compost conversion. Maturity indicators—germination index (GI), total nitrogen (TN), and pH—are strongly positively correlated with beneficial bacterial phyla such as Proteobacteria, Actinobacteria, and Chlorophytes, which contribute to nitrogen retention, organic matter decomposition, and aerobic compost stabilization. These groups are particularly abundant in modified biochar treatment (T3) and are closely associated with improved compost quality. Conversely, cumulative CH4, N2O, and CO2 emissions are positively correlated with Firmicutes, Cyanobacteria, and Desulfurizers, which are typically involved in anaerobic metabolism, fermentation, and incomplete nitrogen cycling. Electrical conductivity (EC), an indicator of compost salinity and phytotoxicity, is positively correlated with these emission-related phyla and negatively correlated with GI and TN, suggesting an antagonistic effect on compost quality. Verrucomicrobiota, Nitrospirota, and Planctomycetota are also negatively correlated with GI and TN, suggesting that their continued abundance may delay compost maturation. Overall, the correlation analysis validated the ecological interactions inferred from principal component analysis and microbial sequencing data. In particular, Na2HPO4-modified biochar fostered microbial communities, enhanced nutrient conservation, promoted compost maturation, and effectively reduced greenhouse gas emissions. Therefore, this integrated approach provides a comprehensive strategy for optimizing compost performance and environmental sustainability.

[0108] In summary, this invention systematically investigated the effects of diatomaceous earth, raw biochar, and Na2HPO4-modified biochar on cow manure co-composting, focusing on compost quality, nitrogen retention, greenhouse gas (GHG) emissions, and microbial community dynamics. The results showed that, compared to the control, all modifiers improved compost maturity, reduced CH4 and N2O emissions, and improved nitrogen retention. Notably, Na2HPO4-modified biochar exhibited superior performance, primarily due to its enhanced surface chemistry and ability to cultivate nitrogen-converting microbial communities. High-throughput sequencing and multivariate analysis revealed strong correlations between microbial migration, improved physicochemical conditions, and reduced greenhouse gas emissions. These findings highlight the synergistic effect of structural and microbial mechanisms in influencing compost performance. Therefore, this invention provides a scientific basis for the selection and engineering design of compost additives to improve environmental sustainability and nutrient recycling.

[0109] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing modified biochar, characterized in that, Includes the following steps: The modified biochar was obtained by impregnation method, adding corn straw biochar to Na2HPO4 solution at a solid-liquid ratio of 1g:10mL, adjusting the pH of the mixture to 11 with alkali solution, and then performing magnetic stirring reaction. After the reaction was completed, the modified biochar was obtained by centrifugation, washing and drying. The concentration of the Na2HPO4 solution is 0.56 mol / L.

2. The method for preparing modified biochar according to claim 1, characterized in that, The particle size of the corn stalk biochar is 0.1-0.2 mm.

3. The method for preparing modified biochar according to claim 1, characterized in that, The preparation process of the corn straw biochar is as follows: The corn stalk powder was heated to 425-475℃ at a heating rate of 10℃ / min, and deheated at this temperature for 2 hours to obtain the corn stalk biochar.

4. The method for preparing modified biochar according to claim 1, characterized in that, The magnetic stirring conditions are as follows: magnetic stirring in a constant temperature water bath at 50℃ for 6 hours.

5. The application of the modified biochar prepared by the preparation method according to any one of claims 1-4 in the field of aerobic composting, characterized in that, In the aerobic composting process, the amount of modified biochar added is 5 wt.% of the fertilizer.

Images