Modified biochar as well as preparation method and application thereof

Abstract

The invention discloses modified biochar as well as a preparation method and application thereof, and belongs to the technical field of aerobic composting additives, the preparation method of the modified biochar comprises the following steps: adding corn straw biochar into a Na2HPO4 solution according to a solid-to-liquid ratio of 1g: (5-10) mL by adopting an impregnation method, adjusting the pH value of a mixed system to 10.8-11.2 by adopting an alkali liquor, and stirring to obtain a mixed solution; then carrying out magnetic stirring reaction, and after the reaction is finished, carrying out centrifugal separation, washing and drying to obtain the modified biochar. The prepared modified biochar is used as an aerobic composting additive, so that greenhouse gas emission can be remarkably reduced, nitrogen retention and compost nutrient content are improved, compost maturity is promoted, plant toxicity is reduced, and a microbial community structure is directionally regulated and controlled. According to the invention, the functionality of the biochar is enhanced through chemical modification, the synergism of pollution reduction, synergism, carbon sequestration and decay promotion is realized, and an effective technical path is provided for realizing low-carbon, efficient and sustainable organic waste resource utilization.

Description

Technical Field

[0001] The invention belongs to the technical field of aerobic composting additives, and in particular relates to modified biochar and a preparation method and application thereof. Background Art

[0002] With the rapid development of animal husbandry and the continuous expansion of livestock and poultry farming, the amount of organic waste, especially manure, generated has increased dramatically. Aerobic composting, as an effective technology for converting livestock and poultry manure into a 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] First, incomplete or low-maturity compost releases a large amount of low-molecular-weight organic acids (such as acetic acid and propionic acid) during microbial degradation. These substances are phytotoxic and can inhibit seed germination and crop growth, seriously affecting the agricultural value of compost products. In addition, nitrogen loss is serious during the composting process, mainly in the form of ammonia (NH3) volatilization and nitrous oxide (N2O) emissions, which reduces the nutrient content of the fertilizer. CH4 and N2O are potent greenhouse gases with a global warming potential (GWP) much higher than CO2. CH4 in compost can contribute up to 80% of the GWP. 100 , and N2O accounts for 50–90% of nitrogen-rich waste compost. Therefore, while traditional composting processes achieve resource utilization, they also become a significant source of greenhouse gas emissions, restricting their sustainable development.

[0004] In order to deal with the above problems, researchers have tried 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 absorb NH3, NH4 + and NO x Gases such as biochar and diatomaceous earth reduce nitrogen loss, while providing a habitat for microorganisms and promoting the degradation of organic matter. Diatomaceous earth, as a natural porous siliceous material, also has high porosity, large specific surface area and good water retention and air permeability. It can improve the structure of the pile and enhance microbial activity. It is also regarded as a potential compost improver. However, although biochar and diatomaceous earth have improved the quality of compost and reduced gas emissions to a certain extent, their mechanism of action still mainly relies on physical adsorption and structural improvement. Their ability to directionally regulate microbial communities is limited, and there are bottlenecks in long-term stability, nitrogen retention efficiency and greenhouse gas emission reduction effects.

[0005] Furthermore, existing research has largely focused on the use of raw biochar or diatomaceous earth alone, lacking systematic investigations of different types of additives, particularly chemically modified biochar. Furthermore, in-depth molecular ecological insights into how these additives influence the succession patterns of core compost microbial communities (such as Proteobacteria, Bacteroidetes, and Actinobacteria), and their coupling with CH4 and N2O emissions, remain lacking. This lack severely limits the scientific selection and precise regulation of compost additives, hindering the widespread application of efficient, low-carbon, and sustainable composting technologies. Summary of the Invention

[0006] In response to the above technical problems, the present invention proposes a modified biochar and a preparation method and application thereof.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing modified biochar comprises the following steps:

[0009] The corn straw biochar is added to a Na2HPO4 solution at a solid-liquid ratio of 1 g: 5-10 mL by an impregnation method, and the pH of the mixed system is adjusted to 10.8-11.2 by an alkaline solution. The mixture is then subjected to magnetic stirring for reaction. After the reaction is completed, the mixture is centrifuged, washed, and dried to obtain the modified biochar.

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

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

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

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

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

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

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

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

[0018] This invention establishes a systematic and synergistically optimized system for preparing modified biochar. First, a specific temperature-controlled pyrolysis process—pyrolyzing corn straw powder to 425-475°C at a heating rate of 10°C / min and maintaining the temperature for 2 hours—effectively regulates the carbonization degree and pore structure development of the biochar, laying a good physicochemical foundation for subsequent chemical modification. Furthermore, surface chemical modification is achieved by impregnation with a sodium hydrogen phosphate solution. By precisely controlling key parameters such as the solid-to-liquid ratio (1 g:10 mL), the Na₂HPO₄ concentration (0.56 mol / L), and the system pH (11.0), modified biochar is successfully prepared that effectively reduces cumulative emissions of CH₄, N₂O, and CO₂. The parameters defined in this invention are not selected in isolation, but rather are optimized combinations based on a systematic understanding of the biochar's physical and chemical properties, surface chemical behavior, and compostability requirements. This creates a highly efficient, low-carbon, and sustainable technology pathway for the resource utilization of organic waste.

[0019] Optionally, the magnetic stirring condition is: magnetic stirring in a constant temperature water bath at 50° C. for 6 h.

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

[0021] A compost additive comprises the modified biochar.

[0022] The modified biochar is used in the field of aerobic composting. During the aerobic composting process, the modified biochar is added in an amount of 5 wt.% of the fertilizer.

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

[0024] 1. Significantly reduce greenhouse gas emissions: Compared with the control group and original biochar and diatomaceous earth, the modified biochar prepared by the present invention can effectively reduce the cumulative emissions of CH4, N2O and CO2, and has excellent greenhouse gas emission reduction capabilities.

[0025] 2. Improve nitrogen retention and compost nutrient content: The modified biochar prepared by the present invention can significantly increase the total nitrogen (TN) and total organic carbon (TOC) in the compost product, helping to reduce nitrogen loss and increase fertilizer value.

[0026] 3. Promote compost maturity and reduce phytotoxicity: The modified biochar prepared by the present invention can significantly increase the seed germination index (GI) by 27.4%, indicating that the compost is highly mature and has low phytotoxicity, making the product safer and more suitable for agricultural use.

[0027] 4. Optimizing the physical and chemical properties of compost: The modified biochar prepared by the present invention 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. Targeted regulation of microbial community structure: The modified biochar prepared by the present invention can significantly enrich key functional bacteria with nitrogen fixation, organic matter degradation and environmental adaptation functions, such as Devosia (37%) and Mesorhizobium (8%), promote the activity of beneficial microorganisms, and enhance the compost bioconversion process.

[0029] 6. Improve the overall quality and sustainability of compost: This invention enhances the functionality of biochar through chemical modification, achieving the synergy of "pollution reduction, efficiency improvement, carbon fixation, and decomposition promotion", and provides an effective technical path for achieving low-carbon, efficient, and sustainable resource utilization of organic waste.

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

[0031] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0032] Figure 1 This is the structural diagram of the aerobic composting system;

[0033] Figure 2 The effects of different additives on key physical, chemical and biological parameters during cow dung composting; A is temperature, B is pH value, C is electrical conductivity (EC), and D is germination index;

[0034] Figure 3 The graphs show the changes of total organic carbon (TOC) (A) and total nitrogen (TN) (B) during the composting process under different treatments;

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

[0036] Figure 5 Figure 2 is the composition and principal component analysis of microbial communities under different composting treatments; A is the phylum, B is the genus, and C is the relative abundance of dominant taxa at the species level; DF is the heat map of microbial changes under different composting treatments, G is the PCA biplot at the phylum level; H is the principal component analysis biplot at the genus level;

[0037] Figure 6Material characterization diagrams of different compost samples, where A is the XRD spectrum, B is the FTIR analysis diagram, and C is the SEM diagram;

[0038] Figure 7 Figure 3 is a multivariate interaction diagram between compost physicochemical parameters, greenhouse gas (GHG) emissions, and microbial community dynamics under different composting treatments, where A is the principal component analysis of GHG emissions and different treatment conditions, B is the principal component analysis of GHG emissions and composting time, and C is the correlation analysis of compost physicochemical parameters (indicators), GHGs, and microorganisms. DETAILED DESCRIPTION

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting 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 terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0041] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0042] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

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

[0044] The "parts" described in the present invention, unless otherwise specified, refer to parts by mass.

[0045] All raw materials used in this invention were commercially available. Cow dung was sourced from Luxiang, Shuangyang District, Changchun City, after being cleaned of stones and other impurities and then air-dried. The diatomaceous earth used in the experiment was secondary diatomaceous earth powder purchased from Diatomaceous Earth Functional Materials Co., Ltd. Corn stalks were sourced from a farm in Changchun, China.

[0046] The technical solution of the present invention is further illustrated by the following examples.

[0047] Example 1

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

[0049] Step 1: Preparation of biochar

[0050] The corn straw raw material was crushed to a particle size of 50–100 mm and placed in a biogasifier (model: AT / SQ-2000) for pyrolysis treatment. The temperature was raised to 450±25°C at a heating rate of 10°C / min and pyrolyzed at this temperature for 2 hours. After the pyrolysis was completed, the raw material was naturally cooled to room temperature to obtain corn straw biochar. The obtained corn straw biochar was ground and sieved, and biochar particles with a particle size of 0.15 mm were collected and set aside.

[0051] Step 2: Sodium hydrogen phosphate (Na2HPO4) solution impregnation modification

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

[0053] Step 3: Wash and dry

[0054] After the reaction, the modified biochar was centrifuged to collect the solid product; it was then washed repeatedly with distilled water for 5 times and dried to a 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 1 g:5 mL, that is, 50 g corn straw biochar and 250 mL 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 1 g:7 mL, that is, 50 g corn straw biochar and 350 mL Na2HPO4 solution.

[0059] Example 4

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

[0061] Example 5

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

[0063] Comparative Example 1

[0064] Use diatomaceous earth as a compost additive.

[0065] Comparative Example 2

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

[0067] Effect verification

[0068] A 45-day aerobic composting experiment was conducted by adding 5% diatomaceous earth (Comparative Example 1), 5% corn straw biochar (Comparative Example 2), and 5% Na₂HPO₄-modified biochar (Example 1, dry weight basis) to cow dung compost. Four treatments were defined: a 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 agitator, an insulation layer, an air pump for forced aeration, a screen plate to ensure air flow distribution, and a thermometer to monitor the internal temperature; the compost leachate is collected at the base through the drain port, and the gas is discharged through the exhaust port.

[0070] The specific composting process is:

[0071] The mixture (cow manure plus 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 minutes on / 45 minutes off. Samples were collected at 13 time points over 45 days of composting and stored at -20°C for basic analysis and at -80°C for microbial identification.

[0072] 1. Analytical methods for compost characteristics

[0073] The pH and EC of the compost were determined using an MP521 analyzer (Shanghai, China) after extraction with distilled water. Total (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 regularly by chromatography. The surface morphology was characterized using a Hitachi S-4100 scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The samples were coated with 50 nm of chromium (LEICA ACE 660) and imaged using BSE and SE modes under high vacuum (15-20 kV, 100 pA) to distinguish between composition and topographic features. The elemental composition was determined using an energy dispersive spectrometer (EDS) using a 30 mm 2 A Bruker detector and Quantax Esprit 1.9 software were used. ATR-FTIR spectroscopy (PerkinElmer Spotlight 100) was used for analysis in the range of 600–4000 cm -1 Functional groups within the range with a resolution of 4 cm -1 4 scans per sample. Data were processed using Spectrum V6 software. XRD was performed using a RIGAKU D / MAX 2550 / PC, Cu KR radiation, 40 kV / 40 mA, with a scan range of 10 (20, 0.026 I step size) according to JCPDS PDF-2004.

[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 NanoDrop NC2000 and agarose gel electrophoresis. Primers 338F and 806R were used to amplify the V3-V4 region of the bacterial 16S rRNA gene, along with a sample-specific 7-bp barcode. PCR was performed using Fast Pfu DNA Polymerase with 25 cycles of denaturation (98°C, 30 seconds), annealing (53°C, 30 seconds), and extension (72°C, 45 seconds). Amplicons were purified using VazymeDNA Clean Beads, quantified using the Quan-it PicoGreen dsDNA Assay Kit, and pooled and sequenced on the Illumina MiSeq platform (MiSeq Reagent Kit v3) at Shanghai Personal Biotechnology Co., Ltd.

[0076] 3. Seed germination test

[0077] Compost samples were mixed with deionized water at a solid-to-liquid ratio (mass / volume) of 1 g:10 ml and shaken in a thermostatic shaker at 150 rpm for 1 hour. 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. 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, with one-way analysis of variance at a significance level of p < 0.05, to separate treatment means for large data sets. Figures 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 physical and chemical indicators during composting

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

[0084] Temperature is a key indicator of composting efficiency, reflecting the activity of microorganisms and the progress of the process. Composting generally goes through four stages: aerobic, thermophilic, cooling and maturation. Figure 2As shown in center A, all treatments, including diatomaceous earth (T1), raw biochar (T2), modified biochar (T3), and the control (CK), entered a thermophilic phase within the first 10 days. T2 (maximum temperature, 66.2°C, day 5) was the highest, followed by T3 (maximum temperature, 65.2°C, day 6), T1 (maximum temperature, 62.5°C, day 8), and CK (maximum temperature, 60.2°C, day 9). Compared to the control, temperatures in treatments T2, T3, and T1 increased by 11.7%, 7.4%, and 5.6%, respectively. All treatments maintained high temperatures (>55°C) for at least 5 days, meeting the standard for harmless manure (GB7959) and ensuring pathogen inactivation. Increased temperatures were closely associated with increases in microbial biomass and metabolic activity. Biochar significantly promoted this effect by enhancing aeration, reducing compost bulk density, and stabilizing carbon content through its porous structure. Furthermore, the biochar-immobilized microbial community further accelerated organic matter degradation, enhancing thermophilic conditions, and promoting compost maturation. After 45 days, the temperatures 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 organic matter biodegradation. Figure 2 As shown in Figure B, due to the alkalinity of diatomaceous earth and biochar, the pH of all treatments increased during the initial composting period and gradually became higher than that of the control (CK). After day 10, the pH decreased, likely driven by organic acid production from microbial nitrification and decomposition. Subsequently, the pH increased until day 25, reflecting organic acid degradation, ammoniation, and the conversion of organic nitrogen to ammonium. Peak pH values ​​during the stabilization period (40 days) were 8.5 (CK and T1), 8.6 (T2), and 8.5 (T3), respectively, primarily due to ammonia accumulation and organic acid decomposition. By day 45, the pH of all treatments stabilized between 8.0 and 8.6, meeting the requirements for mature compost according to the Organic Fertilizer Standard (NY / T 525-2012).

[0086] Electrical conductivity (EC) significantly affects compost salinity, maturity, phytotoxicity, and plant growth. Figure 2 Center C shows the final EC values ​​of 3.21 (CK), 2.84 (T1), 2.69 (T2), and 2.86 mS cm -1 (T3). Initially, EC increased rapidly due to the release of inorganic matter during organic matter decomposition and the concentration effect caused by 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 reducing soluble salt concentrations. All final EC values ​​were below 4.0 mS cm -1 , meets the required standards, indicating that it is suitable for plant growth.

[0087] The germination index (GI) is used to evaluate the maturity and phytotoxicity of compost. Figure 2 As shown in Figure D, the GI values ​​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 treatments had reached maturity. GI was positively correlated with compost detoxification and quality. Biochar and diatomaceous earth effectively adsorbed toxic compounds, enhancing the detoxification and humification of compost, thereby significantly increasing GI. GI values ​​for all treatments exceeded the compost maturity threshold (>70%, NY / T 525-2021), demonstrating compost non-toxicity and suitability for agricultural use.

[0088] Figure 3 These are the changing curves of total organic carbon (TOC) (A) and total nitrogen (TN) (B) during the composting process under different treatments.

[0089] like Figure 3 As shown in Figure 1, total organic carbon (TOC) gradually decreased before reaching a plateau, reflecting rapid carbon degradation by microbial activity. Final TOC values ​​were 44.38% (CK), 43.14% (T1), 42.10% (T2), and 43.29% (T3). The observed decrease in TOC during the thermophilic phase was primarily due to microbial metabolism of carbon-rich materials into CO₂. The addition of diatomaceous earth (T1) and biochar (T2) enhanced the compost's porosity and aeration, 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] Compost quality and agronomic value depend largely on nitrogen concentration. Figure 3 As shown in Figure B, the T2 treatment significantly increased the total nitrogen (TN) content at maturity (18.56%), CK (16.72%), T1 (17.41%), and T3 (17.95%) (p < 0.05). Under high temperature and alkaline conditions, due to the NH4 + The initial decrease in TN occurred in the first 9 days due to the volatilization of NH3 and the rapid degradation of organic matter. The subsequent increase in total nitrogen was mainly due to the extensive decomposition of organic matter, which reduced the compost quality and nitrogen concentration level through the "concentration effect". The addition of diatomaceous earth and biochar (original and modified) has the characteristics of high porosity and large surface area, which enhances nitrogen retention by promoting the growth of nitrifying bacteria. The structure and active functional groups of biochar also limit the mineralization of organic nitrogen and promote the NH4 + The modified biochar further improves nitrogen retention due to its enhanced buffering capacity, supporting the efficient conversion of organic nitrogen into NH4+ .

[0091] 2. Dynamics of greenhouse gas emissions during aerobic composting

[0092] Figure 4 Greenhouse gas emissions from the composting process under different treatments are shown: A and B represent the CH4 emission rate and cumulative CH4 emissions, respectively; C and D represent the CO2 emission rate and cumulative CO2 emissions, respectively; E and F represent the N2O emission rate and cumulative N2O emission rate, 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 in Figure A, CH4 emissions peaked in the first week of composting, with CK being the highest (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 declined over time due to decreases in temperature and degradable carbon content. Cumulative reductions in CH4 emissions were 40.18% (T3), 38.06% (T2), and 18.07% (T1) compared to the control. Modified biochar mitigated CH4 emissions by improving aeration, reducing bulk density, and enhancing the activity of methane-oxidizing bacteria. Corn straw biochar has a lower activated carbon content than manure and diatomaceous earth additions and may be more effective as a compost bulking agent because activated carbon can increase CH4 emissions. Biochar reduces CH4 emissions by adsorbing activated carbon and CH4 during the composting process. Corn straw biochar reduced activated carbon utilization, inhibited methane production, and enhanced methane oxidation, resulting in lower CH4 emissions compared to diatomaceous earth addition and control treatments. After approximately 15 days, reduced oxygen utilization slowed the decomposition of organic matter, promoted compost stabilization, and significantly reduced CH4 emissions. From Figure 4 As can be seen in Figure C, CO2 emissions initially increased rapidly, followed by a secondary rise and subsequent decline 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 , while CK was 19.29 g kg -1 VS d -1. CO2 emissions are closely related to microbial activity and temperature. Biochar modifications enhance microbial metabolism by improving oxygen diffusion due to their high porosity and surface area. Na2HPO4-modified biochar (T3) significantly reduced CO2 emissions by introducing alkaline active sites that enhance chemical adsorption. Overall, the cumulative CO2 emissions decreased by 17.07% (T1), 10.68% (T2), and 18.52% (T3) compared to the control (e.g. Figure 4 These reductions are attributed to the improved pore structure of diatomaceous earth, which retains water and supports microbial activity, and the enhanced CO 2 adsorption and organic matter stabilization of biochar.

[0094] from Figure 4 As can be seen in Figure E, N2O emissions in all treatments showed a trend of first increasing and then decreasing, which was different from 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 ) significantly reduced peak emissions. Cumulative N2O emissions decreased by 52.12% (T3), 44.28% (T2), and 35.46% (T1) compared to the control. The increases and decreases in emissions from biochar and diatomaceous earth treatments are attributed to their high porosity and surface area, which promote aeration and slow down nitrification and denitrification processes. Peak N2O release on days 7-11 was similar to that of NO3 - The increase in -N concentration was associated with an increase in the concentration of nitrification and denitrification, indicating active nitrification and denitrification, despite the typical thermophilic conditions that are considered unfavorable for these microorganisms. The modified biochar (T3) had the highest N2O reduction rate (71.28%), followed by diatomaceous earth (T1, 68.36%) and original biochar (T2, 65.36%). The modified biochar enhances the microbial reduction process and adsorbs NH3 / NH4 + , limiting the availability of nitrogen substrates and increasing the availability of oxygen to inhibit denitrifying enzymes, thereby promoting the mitigation of N2O. In addition, the aromatization and alkalinity of biochar further reduced N2O emissions by increasing the pH of the compost and inhibiting microbial N2O production.

[0095] 3. Microbial community structure

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

[0097] Bacterial community analysis at the phylum level (e.g. Figure 5 Middle (A) showed that Proteobacteria (27-28%), Bacteroidota (19-23%), Acidobacteriota (10-12%), Chloroflexi (8-10%), and Planctomycetota (3-4%) were the dominant groups, consistent with their roles in cellulolysis and nitrogen cycling. The abundance of Proteobacteria remained stable across treatments, which is associated with reduced N₂O emissions and enhanced nitrogen retention. Biochar (T2) significantly increased Bacteroidetes (17%), promoting organic nitrogen mineralization. Diatomaceous earth (T1) enriched Firmicutes (62.68%) and Chloroflexi (19.86%), promoting aerobic decomposition and suppressing pathogens by improving compost porosity. Compared to the control, the abundance of Planctomycetota was significantly reduced in T1 (32.68%), T2 (26.38%), and T3 (17.86%). In the T3 treatment, the abundance of desulfurizing bacteria and nitrosospira decreased significantly by 28.97% and 33.10%, respectively. The abundance of Verrucomicrobia also decreased by 15.93% (T1) and 11.70% (T2), respectively. Actinomycetes, which are important for degrading recalcitrant organic matter and promoting humification, increased significantly in T1 (19.08%) and T3 (13.61%) compared to CK and T2, 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, inhibiting pathogens, and slowing CO2 release. Similarly, the enrichment of Verrucomicrobiota (33.60%) in T3 supported carbon turnover and compost stability. Biochar promoted the abundance of desulfurizing bacteria in T2 (25.92%), while diatomaceous earth (T1) increased the abundance of nitrosospira (21.37%), both of which affected the nitrogen cycle and indirectly regulated CO2 emissions.

[0098] At the genus level (e.g. Figure 5(As shown in Figure B), the relative abundance of Altererythrobacter (12-17%) increased significantly in all treatments at T2. Devosia (26-37%) was significantly enriched in T3 compared to the control, but decreased in T1 and T2. Luteimonas (9-15%) increased significantly in T2, while Lysobacter (4-6%) did not differ significantly among treatments. Mesorhizobium abundance (5-8%) remained largely unchanged compared to the control, but increased slightly (8%) in T3. Conversely, Oleobacteria (6-11%) decreased significantly in all treatments compared to the control. Pseudomonas (3-5%) and Sphingomyelia (4-5%) did not change significantly among treatments. Streptomyces was significantly enriched in T2 (4-11%), while Woeseia (7-11%) was significantly less abundant than in the control. Functionally, Luteomonas exhibited diverse roles in nitric oxide reduction, denitrification, and carbon oxidation, particularly in mature composts. Altererythrobacter, Devosia, and Streptomyces became abundant during the mature stage of composting, promoting the turnover of recalcitrant carbon compounds and playing an important role in nitrite ammonification. Furthermore, Mesorhizobium and Pseudomonas were dominant genera involved in aerobic ammonification, denitrification, and both dissimilatory and assimilatory nitrate reduction, highlighting their key roles in nitrogen cycling during composting.

[0099] Figure 5 Heatmaps shown in Figures D, E, and F illustrate changes in microbial community composition at the phylum, genus, and species levels across the 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 was predominant in the control (CK). At the genus level, Mesorhizobium 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 revealed that denitrifying Pseudomonas predominated in both T2 and T1 treatments, suggesting its involvement in the denitrification pathway. Furthermore, methanotrophic species, such as Methylococcus marineus and Methylomicrobes, were consistently identified across all treatments, highlighting their roles in methane oxidation, heat tolerance, and enhanced biofiltration efficiency. In summary, the addition of additives during composting significantly reshaped the structure and function of the microbial community, promoting the significant enrichment of microbial taxa involved in nitrogen transformation and methane oxidation.

[0100] Principal component analysis (PCA) clearly illustrated the effects of compost additives on microbial community composition. Figure 5Each amendment produced a specific microbial assemblage: diatomaceous earth (T1) significantly enriched Firmicutes and Chlorophytes, while biochar (T2) favored Cyanobacteria and Desulfurobacteria. The modified biochar treatment (T3) had the most significant effect, with significant increases in both Actinobacteria and Proteobacteria, which are essential for nitrogen cycling. Figure 5 In the H-phase, modified biochar (T3) significantly increased the relative abundance of Devosia and Mesorhizobium, which favor nitrogen fixation and compost maturation. Biochar (T2) strongly enriched Streptomyces and Luteomonas, two genera recognized for their roles in organic matter degradation. Overall, these microbial changes support the improved compost maturity and quality, as well as the substantial reduction in greenhouse gas emissions achieved through the treatment.

[0101] Figure 6 A is the XRD spectrum of compost samples CK, T1, T2, and T3, B is the FTIR analysis diagram, and C is the SEM diagram.

[0102] from Figure 6 As can be seen in Figure A, in CK, peaks at 26.5, 28.2, 29.3, and 39.3 degrees correspond to quartz, calcite, and potentially phosphate or potash phases, commonly associated with raw cattle manure compost. The intensified peak observed at 26.5 degrees in T1 confirms the incorporation of silicon-rich diatomaceous earth, attributed to its crystalline SiO2 structure. In contrast, the peaks at 26.5, 28.2, and 29.3 degrees decreased in intensity in treatments T2 and T3, indicating an increase in amorphous content due to biochar. Furthermore, new peaks at 23.62 degrees (T1), 27.72 degrees (T2), and 23.49 degrees (T3) may represent surface modifications 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 cattle manure compost remained consistent across all treatments.

[0103] FTIR analysis (such as Figure 6 (B) The main functional groups responsible for chemical transformation in compost samples CK, T1, T2, and T3 were identified. 3400 cm -1 The broad band nearby corresponds to the OH stretching vibration of hydroxyl groups, alcohols, phenols, and organic acids. 2920 ~ 2850 cm -1 and 2350 cm -1 The peaks at 1640~1651cm represent the aliphatic C-H and O=C=O stretching vibrations of CO2. -1 The bands are caused by the skeletal vibration of aromatic C=C, C=O stretching of amides (amide I), quinones or H-bonded conjugated ketones. 1540~ 1410 cm -1The band reflects the asymmetric stretching of carbon and oxygen, deformation of carboxyl OH and bending vibration of amide NH. -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 composted materials was characterized using SEM (e.g. Figure 6 Figure 3 (C), reveals significant differences between treatments. The control (CK) exhibited a dense, amorphous structure with limited porosity. In contrast, T1 maintained the porous structure typical of diatomite, while T2 and T3 displayed a distinct honeycomb morphology with surface stratification, significant etching, and increased pore complexity. These changes indicate substantial physicochemical transformations and enhanced microbial colonization potential during composting. The observed morphological changes emphasize the important role of modified biochar in enhancing aeration, stimulating microbial activity, and improving the overall quality of the compost. Furthermore, the mineral structure associated with the biochar, detected by scanning electron microscopy, indicated improved nutrient availability and compost maturity, which may be related to the increased pH.

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

[0106] Figure 7 The figure shows the multivariate interaction diagram between compost physicochemical parameters, greenhouse gas (GHG) emissions and microbial community dynamics under different composting treatments, where A is the principal component analysis of greenhouse gas emissions and different treatment conditions, B is the principal component analysis of greenhouse gas emissions and composting time, and C is the correlation analysis of compost physicochemical indicators, greenhouse gases and microorganisms. Among them, CK (control group), T1 (diatomaceous earth compost), T2 (biochar compost) and T3 (modified biochar compost), W1-W8 represent weeks 1 to 8, respectively. The first two principal components (PC1: 51.1%; PC2: 24.1%) accounted for 75.2% of the total variance, showing a strong explanatory power. PCA of different treatment conditions and greenhouse gas emissions (such as Figure 7 The analysis (shown in Figure 5A) illustrates the clear differences between the different compost treatments. The control (CK) was strongly associated with CH4, CO2, and N2O carriers, indicating increased emissions and suboptimal compost maturity. In contrast, the Na2HPO4 modified biochar treatment (T3) was positively correlated with total nitrogen (TN), germination index (GI), and a higher pH, directly antagonizing greenhouse gas carriers, emphasizing its effectiveness in reducing emissions and improving compost quality. The diatomaceous earth (T1) and original biochar (T2) treatments were in the middle, indicating moderate improvements. Figure 7(B) further differentiated compost dynamics, identifying an early cluster (weeks 1-3) associated with higher TOC, EC, and GHG emissions, transitioning to a late cluster (weeks 7-8) characterized by increased GI and TN, reflecting compost stability. These temporal shifts correlated closely 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 the ability of Na2HPO4-modified biochar amendment to reshape compost physicochemical conditions and microbial communities, promoting compost maturation and reducing environmental impacts.

[0107] To further explore the relationships among physicochemical properties, greenhouse gas (GHG) emissions, and microbial communities, correlation analyses were performed on various physicochemical indicators, GHGs, and microbial communities (e.g. Figure 7 (C). Statistically significant correlations highlight the complex microbial-chemical interactions driving compost transformation. Maturity indicators—germination index (GI), total nitrogen (TN), and pH—were strongly positively correlated with beneficial bacterial phyla (such as Proteobacteria, Actinobacteria, and Chlorobacteria), which contribute to nitrogen retention, organic matter decomposition, and aerobic compost stability. These taxa were particularly abundant in the modified biochar treatment (T3) and were strongly associated with improved compost quality. Conversely, cumulative CH₄, N₂O, and CO₂ emissions were positively correlated with Firmicutes, Cyanobacteria, and Desulfurobacteria—bacteria often associated with anaerobic metabolism, fermentation, and incomplete nitrogen cycling. Electrical conductivity (EC), an indicator of compost salinity and phytotoxicity, was positively correlated with phyla associated with these emissions and negatively correlated with GI and TN, suggesting antagonistic effects on compost quality. Verrucomicrobiota, Nitrospirota, and Planctomycetota were also negatively correlated with GI and TN, suggesting that their continued abundance may delay compost maturity. Overall, correlation analyses validated the ecological interactions inferred from principal component analysis and microbial sequencing data, particularly that 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 composting performance and environmental sustainability.

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

[0109] The above are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing modified biochar, characterized in that: The following steps are involved: The corn straw biochar is added to a Na2HPO4 solution at a solid-liquid ratio of 1 g: 5-10 mL by an impregnation method, and the pH of the mixed system is adjusted to 10.8-11.2 using an alkaline solution. The mixture is then subjected to magnetic stirring for reaction. After the reaction is completed, the mixture is centrifuged, washed, and dried to obtain the modified biochar.

2. The method for preparing modified biochar according to claim 1, wherein: The particle size of the corn straw biochar is 0.1-0.2 mm.

3. The method for preparing modified biochar according to claim 1, wherein: The preparation process of the corn straw biochar is as follows: The corn straw powder is heated to 425-475° C. at a heating rate of 10° C. / min, and depyrogenated at this temperature for 2 hours to obtain the corn straw biochar.

4. The method for preparing modified biochar according to claim 1, wherein: The solid-liquid ratio is 1 g:10 mL.

5. The method for preparing modified biochar according to claim 1, wherein: The concentration of the Na2HPO4 solution is 0.56 mol / L.

6. The method for preparing modified biochar according to claim 1, wherein: The pH of the mixed system is 11.

7. The method for preparing modified biochar according to claim 1, wherein: The magnetic stirring conditions are: magnetic stirring in a constant temperature water bath at 50° C. for 6 h.

8. Application of the modified biochar prepared by the preparation method according to any one of claims 1 to 7 in the field of aerobic composting, characterized in that: During the aerobic composting process, the modified biochar is added in an amount of 5 wt.% of the fertilizer.

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