Effect of weathered coal on spectral changes of dissolved organic matter during sheep manure composting

Effect of weathered coal on spectral changes of dissolved organic matter during sheep manure composting | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effect of weathered coal on spectral changes of dissolved organic matter during sheep manure composting Yongjian Liu, Jun Li, Limin Yuan, Zhao Yang, Litong Ma This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6995195/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 20 Dec, 2025 Read the published version in Waste and Biomass Valorization → Version 1 posted 5 You are reading this latest preprint version Abstract The effects of weathered coal on the maturity of sheep manure compost were investigated by studying the spectral changes in dissolved organic matter (DOM) in sheep manure compost. Sheep manure was used as the raw material for compost fermentation, with 10% and 15% weathered coal added. Total organic carbon analysis, ultraviolet-visible absorption spectroscopy, Fourier transform infrared spectroscopy, fluorescence spectroscopy, and three-dimensional excitation emission matrix fluorescence spectroscopy were used to study the spectral changes in DOM in sheep manure compost after the addition of different proportions of weathered coal. Weathered coal had a significant effect on DOM during sheep manure composting. The non-humic organic matter with the same DOM concentration continued to condense to produce humus, increasing the benzene ring structure of the organic matter and enhancing the humification degree of the compost, indicating that the degree of compost maturation increased. Additionally, a portion of humic acid was converted to fulvic acid during composting, and the addition of 15% weathered coal accelerated the composting process. The addition of weathered coal facilitated the synthesis of humic acid in DOM and reduced the soluble salt content in sheep manure. The findings provide a theoretical basis for the collaborative and comprehensive utilization of aquaculture waste and weathered coal resources. Compost Dissolved organic matter Sheep manure Spectral changes Weathered coal Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction In recent years, with the rapid development of sheep farming, the discharge of large amounts of sheep manure has caused serious environmental pollution (Cai et al., 2023). Aerobic composting is the primary method used to manage sheep manure (Li et al., 2024 ). Sheep manure is transformed into high-quality organic fertilizer through composting, reducing the pollution caused by sheep manure accumulation in the surrounding environment (Cai et al., 2024), improving its utilization rate, and increasing soil fertility. During aerobic composting of sheep manure, it is usually necessary to add high-carbon materials to adjust the carbon-to-nitrogen ratio and porosity of the organic fertilizer, which can promote the degradation of organic matter and improve the quality of the compost (Liu et al., 2024 ). In recent years, dissolved organic matter (DOM) in sheep manure composting has been characterized to investigate the structural evolution and degree of humification of organic matter. DOM is a macromolecular organic mixture with a complex structure produced after the humification of organic matter in sheep manure. It is a variable component of organic matter in organic fertilizers, and its structural characteristics change as the compost stabilizes (Wang et al., 2024 ). Yang et al. (2024) used three-dimensional fluorescence spectroscopy to demonstrate that the DOM treatment of low-concentration mature chicken manure compost reduced the bioavailability and migration risk of lead in soil, while increasing microbial abundance and diversity. These changes were more conducive to protecting the normal ecological function of soil. Song et al. (2023) used ultraviolet-visible absorption spectroscopy (UV-Vis) and three-dimensional fluorescence spectroscopy to demonstrate that biochar and montmorillonite can promote humification in chicken manure compost, improving both humification efficiency and carbon fixation during the composting process. Kong et al. (2023) used X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) to detect DOM evolution in the composting process of chicken and pig manure. The study revealed that struvite, calcite, and other crystal structure substances, cellulose, protein, carbohydrates, and microbial byproducts gradually decomposed, while humic acid content gradually increased during the process. The evolution of DOM is related to changes in the physical and chemical environments of compost. The maturity of compost can be observed through the content of humic acid, protein, carbohydrate, degree of aromatization in DOM, and crystal structure of the compost solid phase. Ma et al. (2024) added shell powder to cow manure for composting. The powder reduced CH 4 and CO emissions, and increased carbon fixation during composting, and significantly improved compost quality. Weathering coal refers to a type of mineral resource formed by the long-term weathering of lignite, bituminous coal, and anthracite, either exposed to the surface or located in the shallow layers of the surface (Ma et al., 2024). The chemical composition and physical and chemical properties of weathered coal are different from those of raw coal. For example, its carbon and hydrogen content is low, while it contains more oxygen-containing acidic functional groups. The organic matter content in weathered coal can reach 40–80%, most of which is recycled humic acid (Wang et al., 2024 ). The humic acid in weathered coal has a larger cation exchange capacity, a more porous structure, and more active functional groups (Zhang et al., 2023 ). These characteristics enable weathered coal to exchange, chelate, and absorb nutrients in soil and fertilizer, allowing it to be more easily degraded by soil microorganisms (Zhang et al., 2017). In this study, sheep manure was used as the raw material, with the addition of weathered coal. The changes in DOM during the composting process were measured using UV-Vis spectroscopy, fluorescence spectroscopy, FTIR, 3D-EEM, pH, and conductivity analysis. The study examined the influence of weathered coal on the composting process of sheep manure and analyzed the structural evolution of organic matter and the degree of humification in organic fertilizers. This study aimed to provide a theoretical basis for the comprehensive collaborative utilization of aquaculture waste and low-quality coal resources. 2. Experimental methods 2.1 Sheep manure compost and DOM preparation The weathered coal was obtained from Xinjiang Qinghua Energy Group Co. Ltd. and sheep manure from a farm in Machi Town, Baotou City, Inner Mongolia. Fermentation of organic fertilizer was conducted in a vegetable greenhouse in Machi Town, Baotou City, Inner Mongolia. Different proportions of weathered coal and sheep manure were evenly mixed for composting and fermentation: 0% weathered coal with 100% sheep manure, 10% weathered coal with 90% sheep manure, and 15% weathered coal with 85% sheep manure. The compost made from pure sheep manure (0% weathered coal) served as the control group. The fermentation process lasted for 15 days, with the compost pile turned every 3 days. Fertilizer samples of sheep manure compost were collected as the raw material for DOM extraction. 2.2. Extraction of DOM Freshly acquired samples of sheep manure compost were weighed according to the dry matter weight of organic fertilizer; the volume of double steaming water is 1:10 (W (g)/V(mL)). The mixture was oscillated in a culture oscillation chamber at 200 r·min − 1 at 27 ℃ for 16 h, followed by centrifugation at 8000 rpm at 4 ℃ for 30 min. The supernatant was collected and filtered through a 0.45 µm filter membrane to obtain the DOM as filtrate. The total organic carbon (TOC) content of the DOM in the fertilizer sample was determined using TOC-L CPH. The sample concentration was adjusted to 100 mg(C)·L − 1 with double distilled water. Double-distilled water was used as blank. 2.3. Spectral analyses For UV-Vis spectral analysis, the DOM concentration of the fertilizer sample was adjusted to 100 mg(C)·L − 1 . A UV-Vis spectrophotometer was used to measure the absorbance of the compost sample daily over a scanning wavelength range of 200–700 nm. For fluorescence spectral analysis, both emission and excitation monochromators were set to a scanning speed of 1200 nm·min − 1 , with a slit width of 5 nm. The fluorescence emission spectrum had a scanning range of 370–600 nm and a fixed excitation wavelength of 350 nm. The excitation spectrum used a fixed emission wavelength of 560 nm and the excitation spectral scanning range was 300–550 nm. Synchronous scanning excitation spectra ranged from 300–600 nm, with a photomultiplier spectral width (Δλ) of 18 nm and voltage of 700 V. The instrument used was an F-2700 molecular fluorescence spectrometer (HITACHI, Tokyo, Japan). The concentration of DOM in the fertilizer sample was 100 mg(C)·L − 1 . For FTIR analysis, 1 mg of freeze-dried DOM and 100 mg of chromatographically pure potassium bromide were finely ground, mixed, and pressed into thin slices. The infrared spectrum of the sample was measured and recorded using a FTIR spectrometer. 3D-EEM fluorescence spectroscopy characteristics of DOM (100 mg(C)·L − 1 ) of compost samples were determined using a fluorescence spectrophotometer. The sample was placed in a 10 mm quartz colorimetric dish, with ultrapure water as the blank. The excitation wavelength (Ex) was scanned from 200–600 nm in 10 nm intervals, and the emission wavelength (Em) was scanned from 220–600 nm in 5 nm intervals, with a scanning speed of 48000 nm·min − 1 . The photomultiplier tube gain was set to 650 V, and the response time was automatically matched. Finally, pH and conductivity were determined for the initial DOM that had not been adjusted by concentration using a pH meter and a conductivity meter. 3. Results and discussion 3.1. UV-Vis spectrum analysis of DOM in sheep manure composting with weathering coal The specific ultraviolet absorbance at 254 nm (SUVA 254 ) was defined as a ratio of 100 times the absorbance of the DOM in organic fertilizer at 254 nm to the TOC of the DOM solution. Yang et al. (2024) suggested that the UV absorption of organic matter at 254 nm mainly represents compounds with unsaturated carbon-carbon bonds, such as aromatic compounds. At 254 nm, the increase in the light absorption value indicates the conversion of non-humic organic matter to humus with the same DOM concentration (Liu et al., 2023), further indicating an increased degree of decomposition of compost. The UV absorption intensity of DOM in sheep manure compost at 254 nm in the absence and presence of 10% or 15% weathered coal are presented in Fig. 1 . In the absence of weathered coal a decrease in absorbance from 0.173 to 0.101 was followed by an increase to 0.162. In the presence of 10% weathered coal, the absorbance decreased from 0.210 at the beginning of composting to 0.138 and finally increased to 0.177. In the presence of 15% weathered coal, the absorbance increased from 0.177 at the beginning of composting and finally increased to 0.734. The results showed that macromolecular substances, such as humic acid, cellulose, hemicellulose, lignin, and proteins, contained in the DOM during the early fermentation stage were gradually degraded by the microorganisms. At 254 nm, the absorbance of DOM increased and the amino acid and lignin degradation products continued to condense to form humic acids. The humus of sheep manure organic fertilizer continued to increase, and the degree of humification increased with the fermentation of the fertilizer (Zhang et al., 2024 ). The absorbance value at 254 nm of 0.734 in the presence of 15% weathered coal manure compost was higher than that of 0.177 in the presence of 10% weathered coal and 0.162 in the absence of weathered coal. The increased absorbance values indicated that organic non-humus with the same DOM concentration continuously condensed into humus and increased compost maturation (Danil et al., 2024 ). The findings indicate that the addition of weathered coal promoted an increase in humic acid in the sheep manure compost, and the addition of 15% weathered coal compost promoted the humification of sheep manure compost. 3.2. E 4 /E 6 analysis of DOM in sheep manure composting by weathering coal UV-Vis light absorbances at 465 and 665 nm were defined as E 4 and E 6 (Lan et al., 2022 ), respectively. E 4 /E 6 is the ratio of the absorbance of DOM at 465 and 665 nm. This ratio is often used to characterize the stability of organic matter in the composting process. The smaller the value of E 4 /E 6 , the greater the complexity of macromolecular organic matter (Zhou et al., 2023), that is, the greater the degree of polymerization of organic matter. Figure 2 shows the E 4 /E 6 of the UV-Vis spectrum of DOM in sheep manure compost with 10% or 15% weathered coal. The E 4 /E 6 value of the sheep manure compost with the addition of weathered coal gradually increased to its highest value at the beginning of composting, indicating that the DOM of the compost sample decreased convertible organic matter, such as lignin and cellulose, in the sheep manure during the fermentation process. The macromolecular matter decomposed, the degree of polymerization of organic matter decreased, and then the E 4 /E 6 value decreased at the end of the organic fertilizer fermentation. After decomposition, pyruvate, amino acids, and other small molecules of organic matter begin to polymerize, and the continuous synthesis of humic acid substances increases the degree of organic matter polymerization (Dong et al., 2024). As shown in Fig. 2 , the E 4 /E 6 value of sheep manure compost without weathered coal increased from 6.222 at the beginning of composting to 6.647 at the end. The DOM of the sheep manure organic fertilizer with 10% weathered coal increased the degree of product polymerization from the beginning to the end of composting. The value of E 4 /E 6 decreased from 5.444 at the beginning to 5.121 at the end of the composting process, indicating that large molecules, such as cellulose, lignin, and protein, first decomposed to form smaller organic compounds that included pyruvate and amino acids. As composting progressed, humic acids were synthesized, which increased the degree of polymerization of organic matter. The DOM of sheep manure organic fertilizer amended with 15% weathered coal showed a decrease in the degree of polymerization from the beginning to the end of composting, similar to that of sheep manure compost without weathered coal. The E 4 /E 6 value increased from 4.322 at the beginning to 4.608 at the end of composting. However, the E 4 /E 6 value was the lowest at the beginning of composting. The results showed that sheep manure organic fertilizer with 15% weathered coal initially contained more macromolecular organic matter, and during the composting process, the macromolecular organic matter decomposed first to form small molecular organic matter. As composting progressed, humic acid substances began to be synthesized, and the degree of polymerization of the organic matter increased. The addition of weathered coal increased the degree of organic matter polymerization and humification in the sheep manure compost. At the end of composting, the E 4 /E 6 value of 4.608 for sheep manure organic fertilizer with 15% weathered coal was lower than 5.121 of the organic fertilizer with 10% weathered coal, indicating that the organic matter of sheep manure organic fertilizer with 15% weathered coal had a greater degree of polymerization and compost humification, further indicating that the degree of compost decomposition increased. 3.3. Fluorescence spectrum characteristics of DOM in sheep manure composting in the presence of weathering coal Figure 3 a shows the synchronous scanning fluorescence spectrum for 0% weathered coal, whereas Fig. 3 b and c display the spectra for 10% and 15% weathered coal added to sheep manure compost, respectively. The spectra indicate that different DOM components have different absorption intensities at different wavelengths, and this method is commonly used to characterize the degree of humification in compost (Marta et al., 2024). In the spectra of sheep manure compost with weathered coal (Fig. 3 b and c), the DOM of the compost showed distinct fluorescence peaks at 360–390, 430–450, and 460–490 nm. However, in the spectrum of compost without weathered coal (Fig. 3 a), the DOM showed fluorescence peaks at 360–390 and 430–450 nm, closely aligning with the characteristic peaks of soil fulvic acid (330–360, 390–430, and 460–490 nm) (Zhao et al., 2023). This suggests that the humic substances in DOM were mainly fulvic acids. As the proportion of aromatic structures in the humic substances increases, a redshift in the spectrum peak occurs (Wu et al., 2023). According to Fig. 3 b and c, the maximum peaks of the three humic peaks (380, 430, and 475 nm) in the fluorescence spectra of the sheep manure compost DOM with the addition of weathered coal moved in the long wave direction and the peaks shifted to the right at 383, 432, and 478 nm, respectively, from the beginning of day 0 to the end of day 15. The fluorescence peak of sheep manure compost DOM in the absence of weathered coal also showed a similar shift. The shift was more pronounced in compost with added weathered coal than in the compost without weathered coal, indicating the presence of thick cyclic aromatic hydrocarbons in the DOM of compost with added weathered coal, resulting in a shift in the maximum fluorescence peak position. This shows that the addition of weathered coal can increase the benzene ring structure of organic matter during composting, increase the degree of conjugation, and improve the stability of the final product (Wang et al., 2021). The DOM synchronous scanning fluorescence spectra, as shown in Fig. 4 , reveal two regions: Region A (330–360, 390–430, and 460–490 nm) represented the fulvic acid fluorescent region (FLR) associated with dense aromatic hydrocarbons with 3–4 benzene rings in fulvic acids. Region B (490–595 nm) is the humic acid fluorescent region (HLR) related to polycyclic aromatic structures of dense aromatic hydrocarbons with 5–7 benzene rings in humic acids (Dong et al., 2019). The fluorescence regions of A FLR and A HLR correspond to the proportion of the fluorescence integral area to the total area in the range of 300–460 and 460–600 nm, respectively. As shown in Fig. 4 , the A FLR values decreased, while the A HLR values increased. The contents of fulvic acids decreased and humic acids increased in DOM components during composting. Because the different components of DOM change during composting, the spectrum moves in the direction of the long wave. The ratio of the A HLR area to the A FLR area (A HLR /A FLR ) was used to reveal the conversion of DOM during composting (Li et al., 2023). As shown in Fig. 4 , A HLR /A FLR continued to increase overall. The A HLR /A FLR ratio of the DOM of composting sheep manure increased from 0.1404 at the beginning to 0.1465 at the end of composting. The A HLR /A FLR of DOM of composting sheep manure in the presence of 10% weathered coal increased from 0.4156 at the beginning to 0.4366 at the end of composting. A HLR /A FLR increased from 0.4732 at the beginning of composting to 0.6299 at the end of composting, indicating that the aromatic structure of humic increased over time, with the final product of composting tending to be stable. The addition of weathered coal was helpful for the decomposition of the sheep manure compost, and the addition of 15% weathered coal was better at promoting the humification of composting sheep manure. As shown in Fig. 4 , the A HLR /A FLR ratio changed, generally in an upward trend. Sheep manure devoid of and amended with 10% weathered coal showed a maximum peak value on day 12; at that time more humic acid was produced by the fermentation reaction than fulvic acid. The A HLR /A FLR ratio was reduced, but still greater than that at the beginning of composting, indicating that a part of the humic acid was converted to fulvic acid during the composting process. The peak of sheep manure with 15% weathered coal appeared earlier than the peak in the other two groups, indicating that 15% weathered coal could accelerate the composting process. 3.4. Influence of weathered coal on three-dimensional fluorescence spectrum characteristics of DOM during sheep manure composting Humic acid in DOM, produced during the composting process, contains benzene ring structures that absorb the excitation light of certain energies. Therefore, a three-dimensional fluorescence spectrum can be used to analyze the evolution of DOM during the composting process (Wei et al., 2022). The three-dimensional fluorescence spectra of water-soluble organic compounds were analyzed using the region integral method. The spectra were divided into five regions. Region I (Ex: 220–250 nm, Em: 290–330 nm) and Region II (Ex: 220–250 nm, Em: 330–380 nm) correspond to protein fluorescence in the aromatic compounds. Region III (Ex: 220–250 nm, Em: 380–500 nm) represents the fulvic acid-like fluorescence region. Region IV (Ex: 250–400 nm, Em: 290–380 nm) defines the dissolved microbial byproduct fluorescence. Region V (Ex: 250–400 nm, Em: 380–500 nm) is associated with humic acid fluorescence (Lu et al., 2024 ). The absorption intensities of different water-soluble organic compounds in the DOM of sheep manure amended with weathered coal differed at different excitation and emission wavelengths. Figures 5 show the three-dimensional fluorescence spectra of DOM during composting with 0% (a-f), 10% (h-m), and 15% (n-s) weathered coal, respectively. Panels a–f in these figures represent the spectra of DOM at 0, 3, 6, 9, 12, and 15 days of composting, respectively. During composting, the fluorescence peak of DOM was approximately Ex/Em = 400 nm/450 nm (Lu et al., 2024 ). Liu et al. (2023) reported that the main source of this fluorescence peak was fulvic acid, which is a water-soluble humic acid. As composting time increased, the intensity of the fluorescence peak first decreased from day 0 to day 3, followed by gradual increases. The fluorescence peaks shifted towards larger emission and excitation wavelengths. As shown in Figs. 5 , the three-dimensional fluorescence spectra of DOM in sheep manure composting, with added weathered coal, and the main peak area of DOM in the sheep manure composting process with the addition of 0% weathered coal was in Region V, indicating that the content of humic acids mainly changed in the composting process (Zhao et al., 2024). The fluorescence peaks of DOM with different proportions of weathered coal showed the same trend: first decreasing and then increasing as composting progressed, with reaching a peak on day 15. This was due to the formation of humic acids under the action of microorganisms. As easily degradable organic matter (hemicellulose, cellulose, and protein) in the compost was consumed, microorganisms began degrading the refractory organic matter, such as lignin. Simultaneously, the previously generated humic acids further transformed into high molecular weight and more stable humic substances, resulting in a continuous increase in humic content and the degree of humification in the compost. Moreover, the observed redshift in the fluorescence peak in the DOM three-dimensional fluorescence spectrum may have been related to the increase in carbonyl, hydroxyl, alkoxy, amino, and carboxylic groups, indicating that the molecular weight, aromatics, and hydrophobicity of DOM increased with the deepening of humification in the compost (Wang et al., 2024 ). In the early stages of composting, the high fluorescence peak was due to the high humic acid content in the weathered coal. Subsequently, decomposition occurred under the action of microorganisms, which reduced the content of humic acid. As the composting days increased, the composition of DOM changed, and its structure transformed into more complex humic acids. Thus, in the composting process, the structure of simple small subclasses of substances continues to decrease, and the structure of complex macromolecular substances continues to increase. At the end of composting, the peak fluorescence of sheep manure organic fertilizer amended with 15% weathered coal was 357.8. This value was higher than the value of 303.7 for sheep manure organic fertilizer amended with 10% weathered coal. Both values exceeded the peak of 287.2 observed in the absence of weathered coal. The results indicate that more humic acids were present in sheep manure organic fertilizer amended with 15% weathered coal, indicating a greater degree of humification. The addition of weathered coal promotes the maturation of sheep manure compost. 3.5. Influence of weathered coal on the infrared spectral characteristics of DOM during sheep manure composting Figure 6 a displays the infrared spectrum of DOM of sheep manure compost in the absence of weathered coal. Figure 8 b and c show the infrared spectra of the DOM of sheep manure compost in the presence of 10% and 15% weathered coal, respectively. In panels b and c, four prominent absorption peaks are present at approximately 3420, 1630, 1385, and 1100 cm − 1 in the infrared spectrum of the DOM. In the control group (spectrum a), similar infrared absorption peaks were present but with low intensity. In addition, several smaller absorption peaks in the range of 500–750 cm − 1 were evident. The absorption peaks in the 3500–3000 cm − 1 range correspond to the stretching vibrations of -OH in -COOH, alcohol, and phenol. The peaks at 1660–1600 cm − 1 may reflect the stretching vibrations of olefin-C = C-, carbonyl (-C = O) groups in carboxylic acid, or -C = O in the associated amides (Wang et al., 2024 ). The peaks at 1420–1300 cm − 1 may be part of the characteristic spectrum of humic materials, reflecting symmetric stretching vibrations of -COO-, -C-O-H curved band, or bonded aromatic ring class. The peaks at 830–820 and 671 cm − 1 are the characteristics of aromatic rings. The 603 cm − 1 peak is the N-H bending band of an amino compound (Yang et al., 2020). The absorption peaks in the ranges 3500–3000 and 1660–1600 cm − 1 indicate that the DOM contains a benzene ring and phenolic functional groups. The presence of absorption peaks at 3500–3000, 1660–1600, and 1420–1300 cm − 1 indicates the presence of -COOH in the compost sample. The absorption spectra displayed in Fig. 6 indicate that while the same functional groups are present in the compost DOM, the contents of some functional groups are different. The increase in the relative intensity of the absorption peak (i.e., the peak value) indicates an increased content of the functional group corresponding to the absorption peak (Guo et al., 2019 ). As compost fermentation progressed, the relative intensity (i.e., peak value) of the DOM absorption peak in the 3500–3000 cm − 1 range generally decreased from day 0 to day 15, indicating that cellulose, hemicellulose, and protein decomposition in the compost raw materials reduced hydroxyl and methyl groups. However, fluctuations were observed during the composting process, with the relative intensity of the absorption peak of all compost DOM at 1300 cm − 1 increasing from day 0 to day 15, indicating an increase in humic substances. Moreover, the intensity of the infrared absorption peak of DOM in sheep manure compost with 15% weathered coal was higher than that of DOM in sheep manure compost with 10% weathered coal, indicating a greater degree of humification in the compost with 15% weathered coal. This suggests that the addition of weathered coal positively affected the fermentation process of sheep manure compost. At the absorption peak in the 600–800 cm − 1 range, the absorption intensity of sheep manure compost with weathered coal was significantly higher than that of compost without weathered coal, indicating that the addition of weathered coal promoted the formation of more stable humic acid aromatic compounds during the composting process. 3.6. Influence of weathered coal on the conductivity of DOM during sheep manure composting The conductivity of DOM during composting reflects the content of soluble salts (both organic and inorganic) present. The high salt content can be detrimental to plant growth, leading to land salinization, water loss in plants, and reduced survival rates. Conversely, too low a salt content indicates insufficient nutrients, which can also affect plant growth (Xiao et al., 2022). Figure 7 shows the change in DOM conductivity during the composting process with the addition of weathered coal. On day 0 of composting, the conductivity was low due to the presence of more macromolecular organic materials in the raw composting materials. As composting progressed, these macromolecular substances—such as humic acid, cellulose, hemicellulose, lignin, and proteins—were decomposed into smaller molecular substances, including water-soluble humic acid, pyruvate, amino acids, and some soluble salts. With the progress of composting, soluble salts were utilized by microorganisms, and some soluble substances were transformed into relatively stable macromolecular organic compounds such as humic acid. Consequently, the electrical conductivity gradually decreased and stabilized (Sun et al., 2023). This trend indicates a reduction in the content of soluble salts (Na + , K + , Ca 2+ , and Cl − ), an increase in humic acids, and an overall increase in the degree of humification during the composting process (Wang et al., 2024 ). The average conductivity of sheep manure organic fertilizer with 15% weathered coal was lower than that of the fertilizer with 10% weathered coal, indicating that the addition of 15% weathered coal facilitated the synthesis of humic acids and reduced soluble salt content, thereby improving the fermentation effect of compost compared with the 10% weathered coal treatment. The conductivity of the DOM in sheep manure compost in the absence of weathered coal was lower than that in the presence of weathered coal, further indicating that the addition of weathered coal promoted the synthesis of humic acid and reduced soluble salt content in sheep manure. 3.7. Influence of weathered coal on the pH of DOM during sheep manure composting During composting, the life activities of microorganisms essentially depend on the appropriate pH, as both excessively high and low values can hinder microbial reproduction and the degradation of organic matter in the compost material. Figure 8 shows how the pH value of DOM in sheep manure compost changes over time with different proportions of weathered coal. The pH of the DOM in the presence of weathered coal generally increased initially and then decreased; however, the presence of easily decomposable ammoniated nitrogen-containing organic matter caused fluctuations in pH. During the early stages of composting, pH first increased to 7.73 and 7.55, respectively, before decreasing to 7.42 and 7.38 by the end of the composting period, remaining within the weakly alkaline range. The initial increase in pH value can be attributed to the production of ammonia from nitrogen-containing compounds in the pile during ammonification, which could not be released into the air in time and remained in the pile. Subsequently, ammonia reacted with water in the compost, generating a trace amount of ammonia, which was transferred to the DOM of the compost, resulting in an increased pH of the DOM (Balasubramani et al., 2022). The pH decreased slightly after day 6 due to the accumulation of organic acids, such as water-soluble humic acid, propionic acid, pyruvic acid, and other carboxylic acids, which resulted from organic degradation, and did not decompose over time. As the compost continued to decompose, humic acids and other substances accumulated in the heap, causing the pH of the compost DOM to become weakly alkaline. Compared with the compost with 10% and 0% weathered coal, the pH value of the DOM in sheep manure compost with 15% weathered coal was consistently lower, not exceeding 7.40. This was lower than the pH values of 7.42 and 7.60 for the DOM in sheep manure compost with 10% and 0% weathered coal, respectively, indicating that more acidic humic acids were generated in the DOM. 4. Conclusions The addition of weathered coal significantly affected the DOM during sheep manure composting, and the degree of humification of the compost increased, indicating an increase in the degree of decomposition of the compost. UV-Vis spectrogram analysis revealed that when 15% of weathered coal was added, the absorbance value at 254 nm increased to 0.734, which is higher than the absorbance values of 0.177 for the compost with 10% weathered coal and 0.162 for the compost without weathered coal. The increase in the absorbance value indicated that non-humic organic matter with the same DOM concentration was continuously condensed into humus, showing increased compost maturation. The addition of weathered coal promoted an increase in humic acid in sheep manure compost, with the 15% weathered coal promoting humification. At the end of composting, the E 4 /E 6 ratio for sheep manure organic fertilizer with 15% weathered coal was 4.608, lower than the 5.121 for fertilizer with 10% weathered coal, indicating that the organic matter in sheep manure organic fertilizer with 15% weathered coal exhibited a greater degree of polymerization and humification in the compost, suggesting an increase in the degree of decomposition of the compost. Fluorescence spectra analysis showed that the addition of weathered coal increased the humus in sheep manure compost, the benzene ring structure of organic matter, conjugation degree, maturity, and stability of the compost fertilizer. Additionally, a portion of humic acid was converted into fulvic acid during composting, and the addition of 15% weathered coal accelerated this process. Analysis of three-dimensional fluorescence spectra demonstrated that at the end of composting, the fluorescence peak of sheep manure organic fertilizer with 15% weathered coal reached 357.8, higher than 303.7 for the fertilizer with 10% weathered coal, and both were larger than 287.2 for the 100% sheep manure organic fertilizer. This indicates more humic acids were present in the fertilizer with 15% weathered coal, suggesting greater humification of the compost. Therefore, the addition of weathered coal promotes the maturation of sheep manure. According to the infrared spectrum analysis, the degree of humification in sheep manure compost with 15% weathered coal was high, indicating that weathered coal facilitated the fermentation process. At the absorption peak of 600–800 cm − 1 , the intensity for compost with weathered coal was significantly higher than that of the control group, indicating that the addition of weathered coal promoted the formation of more stable humic acid aromatic compounds in sheep manure compost during composting. Analyses of pH and conductivity showed that the addition of weathered coal was conducive to the synthesis of humic acid in DOM and reduced the soluble salt content in sheep manure. Declarations CRediT authorship contribution statement Data curation, and Writing-original draft, Yongjian Liu; Formal analysis, Jun Li; Data testing, Yang Zhao; Language polishing, Limin Yuan; Funding acquisition, Methodology, Litong Ma. Funding This work is financially supported by the Inner Mongolia Autonomous Region Science and Technology Plan Project (2025KYPT0175). Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References Mukesh, B.R.N.K., Soon, K.A., Selvi, W.C.P.K., Nur, R.B.S.C.: Ganesh. M. Valorization of food waste and poultry manure through co-composting amending saw dust, biochar and mineral salts for value-added compost production. Bioresour. Technol. 346 , 126442 (2022). https://doi.org/10.1016/j.biortech.2021.126442 Cao, C.R.C.X., Jiang, X., Xu, X.W.R.: Crushing combined with high-frequency turning can promote material degradation of sheep manure compost on the Qinghai-Tibet Plateau by improving the microbial metabolic function. J. Environ. Chem. Eng. 11 (2), 109535 (2023). https://doi.org/10.1016/j.jece.2023.109535 Xu, C.R.L.R.C.X.: Available sulfur and phosphorus transformation mechanism and functional microorganisms during sheep manure composting on Qinghai-Tibet Plateau under two moisture contents. Bioresour. Technol. 394 , 130191 (2024). https://doi.org/10.1016/j.biortech.2023.130191 Danil, G., Kurashev, R.M., Manasypov, T.V., Raudina, I.V., Krickov, A.G., Lim, Oleg, S.: Pokrovsky. Dissolved organic matter quality in thermokarst lake water and sediments across a permafrost gradient. Western Siberia Environ. Res. 252 , 119115 (2024). https://doi.org/10.1016/j.envres.2024.119115 Wei, D.S.L.R.Z.K., Chen, Y.L.J.C.M.: Hu. X. Response of humification process to fungal inoculant in corn straw composting with two different kinds of nitrogen sources. Sci. Total Environ. 946 , 174461 (2024). https://doi.org/10.1016/j.scitotenv.2024.174461 Wang, D.L., Ma, X.: Effect of lignite addition on the characteristics of spectral changes of water-soluble organic matter during sheep manure organic fertilizer fermentation [J]. Spectrosc. Spectr. Anal. 39 (11), 3579–3584 (2019). https://doi.org/10.3964/j.issn.1000-0593(2019)11-3579-06 Guo, X., He, X., Li, C., Li, N.: The binding properties of copper and lead onto compost-derived DOM using Fourier-transform infrared, UV-Vis and fluorescence spectra combined with two-dimensional correlation analysis. J. Hazard. Mater. 365 , 457–466 (2019). https://doi.org/10.1016/j.jhazmat.2018.11.035 Kong, X., Yan, L.G.: Xie. G. Dissolved organic matter evolution can reflect the maturity of compost: Insight into common composting technology and material composition. J. Environ. Manage. 326 (B), 116747 (2023). https://doi.org/10.1016/j.jenvman.2022.116747 Li, Y., Liu, T.Q., Ding, S., Min, W.: Yuan. C. Effects of the combined compost of grape branches and sheep manure on a soil-microorganism-chardonnay (Vitis vinifera L.) plant ecosystem. Sci. Hort. 336 , 113430 (2024). https://doi.org/10.1016/j.scienta.2024.113430 Liu, H., Mukesh, K.A., Asad, Z.Z.: Ali. H.B. Evaluation of gases emission and enzyme dynamics in sheep manure compost occupying with peach shell biochar. Environ. Pollut. 351 , 124065 (2024). https://doi.org/10.1016/j.envpol.2024.124065 Bai, L.C., Zhao, X.: Effects of spring maize straw returning methods on soil DOM spectral characteristics in Cold and arid regions [J]. J. Ecol. Environ. 32 (08), 1419–1432 (2023). https://doi.org/10.16258/j.cnki.1674-5906.2023.08.007 Lan, J., Liu, L., Wang, X., et al.: DOM tracking and prediction of rural domestic sewage with UV–vis and EEM in the Yangtze River Delta, China. 29 , 74579–74590. (2022). https://doi.org/10.1007/s11356-022-20979-4 Li, H., Garrett., M.: Fluorescence Quenching of Humic Substances and Natural Organic Matter by Nitroxide Free Radicals. Environ. Sci. Technol. 57 (1), 719–729 (2023). https://doi.org/10.1021/acs.est.2c02220 Lu, M., Hao, L.B.Z.Y., Li, Y., Huang, K., Li, Z.: Ji. Insight into the molecular transformation pathways of humic acid in the co-composting of bagasse and cow manure after adding compound microorganisms. Process Biochem. 143 , 23–33 (2024). https://doi.org/10.1016/j.procbio.2024.04.029 Wang, L.J., Bao, N.M.F., Hao, Z.W.J.: Wei. Y. Insights into the roles of DOM in humification during sludge composting: Comprehensive chemoinformatic analysis using FT-ICR mass spectrometry. Chem. Eng. J. 475 , 146024 (2023). https://doi.org/10.1016/j.cej.2023.146024 Li, M.L.: A new strategy to increase compost carbon fixation: Shell powder reduced gaseous pollutant emissions in co-composting of cow manure and sawdust. J. Environ. Chem. Eng. 12 (3), 112916 (2024). https://doi.org/10.1016/j.jece.2024.112916 Li, M.L., Liu, L.: Chem. Biol. Eng. 41 (02), 7–12 (2024). https://doi.org/10.3969/j.issn.1672-5425.2024.02.002 Y. Research progress on extraction and application of humic acid from weathered coal [J] Marta, P.R., Llorent-Martínez, A.D.E.J.: María José Ayora-Cañada. Monitoring organic matter transformation of olive oil production residues in a full-scale composting plant by fluorescence spectroscopy. Environ. Technol. Innov. 35 , 103695 (2024). https://doi.org/10.1016/j.eti.2024.103695 Gao, S.C., Sun, Y., Zhao, Q., Qi, Y., Wang, H.C.Z.L.J.: Wei. Z. Insight into the pathways of biochar/smectite-induced humification during chicken manure composting. Sci. Total Environ. 905 , 167298 (2023). https://doi.org/10.1016/j.scitotenv.2023.167298 Zhu, S.H.C.S., Xie, N.P.J.W.J.: Feng. Ya. Hydrothermal carbonization aqueous phase promotes nutrient retention and humic substance formation during aerobic composting of chicken manure. Bioresour. Technol. 385 , 129418 (2023). https://doi.org/10.1016/j.biortech.2023.129418 Wang, W., Zhu, Y., Qu, J.: Effect of DOM derived from composting on the changes of Pb bioactivity in black soil. J. Environ. Chem. Eng. 12 (2), 112232 (2024). https://doi.org/10.1016/j.jece.2024.112232 Wang, K., Yang, Z.X.Z.J.Z.W.: Wang. X. Amended soils with weathered coal exhibited greater resistance to aggregate breakdown than those with biochar: From the viewpoint of soil internal forces. Soil Tillage. Res. 244 , 106244 (2024). https://doi.org/10.1016/j.still.2024.106244 Wu, S., Sun, D.T.: Impact of compost methods on humification and heavy metal passivation during chicken manure composting. J. Environ. Manage. 325 (B), 116573 (2023). https://doi.org/10.1016/j.jenvman.2022.116573 Ren, W.Q., Sun, X., Zhao, Y., Mukesh, J.: Zhang. Z. Improvement of the composition and humification of different animal manures by black soldier fly bioconversion. J. Clean. Prod. 278 , 123397 (2021). https://doi.org/10.1016/j.jclepro.2020.123397 Shen, W.J.S.H., Mi, C., Liu, H.: Zhou. S. Deciphering the structural characteristics and molecular transformation of dissolved organic matter during the electrolytic oxygen aerobic composting process. Sci. Total Environ. 845 , 157174 (2022). https://doi.org/10.1016/j.scitotenv.2022.157174 Wang, W., Zhu, Y., Qu, J.: Effect of DOM derived from composting on the changes of Pb bioactivity in black soil. J. Environ. Chem. Eng. 12 (2), 112232 (2024). https://doi.org/10.1016/j.jece.2024.112232 Wang, H., Li, G.X., Heyong, S., Huang: Insight into the binding characteristics of dissolved organic matter (DOM) and Fe(Ⅱ)/Mn(Ⅱ): Based on the spectroscopic and dialysis equilibrium analysis. Chemosphere. 362 , 142672 (2024). https://doi.org/10.1016/j.chemosphere.2024.142672 Wang, S., Cui, L.P.W.M., Tuo, Y., Zhao, Y.: Wang. N. Evaluation of chemical properties and humification process during co-composting of spent mushroom substrate (Pleurotus ostreatus) and pig manure under different mass ratios. Int. Biodeterior. Biodegrad. 193 , 105858 (2024). https://doi.org/10.1016/j.ibiod.2024.105858 Liu, X.J.W.G., Dai, H.: Application of composted lipstatin fermentation residue as organic fertilizer: Temporal changes in soil characteristics and bacterial community. Chemosphere. 306 , 13563 (2022). https://doi.org/10.1016/j.chemosphere.2022.135637 Zhu, Y.W., Jiang, Y., Jin, Y.Z.J.W.W., Liu, Y.: Qu. J. Dissolve organic matter of mature chicken compost contributes to the protection of microorganisms from the stress of heavy metals. J. Environ. Chem. Eng. 12 (5), 113590 (2024). https://doi.org/10.1016/j.jece.2024.113590 Cui, Y.Y.D.W., Zhao, Z., Lv, T.W.X.: Spectroscopic characteristics of dissolved organic matter during pig manure composting with bean dregs and biochar amendments. Microchem. J. 158 , 105226 (2020). https://doi.org/10.1016/j.microc.2020.105226 Zhang, X., Wang, Z.J.W.K., Xie, X.Z.Z.: Cai. J. Greater mineral and aggregate protection for organic carbon in the soil amended by weathered coal than by biochar: Based on a 3-year field experiment. Geoderma. 438 , 116639 (2023). https://doi.org/10.1016/j.geoderma.2023.116639 Li, Z.S.Y.L., Lin, W., Li, Z., Hu, Y.: Zhao. B. Characterization of pH-fractionated humic acids derived from Chinese weathered coal. Chemosphere. 166 , 334–342 (2017). https://doi.org/10.1016/j.chemosphere.2016.09.095 Zhang, X., Zhu, C.F.Y.D., Zhang, Y.Z.Y.: Effects of wet-dry alternation on organic phosphorus dynamics and sediment characteristics in the intertidal zone of Nansi Lake. Ecotoxicol. Environ. Saf. 281 , 116668 (2024). https://doi.org/10.1016/j.ecoenv.2024.116668 Zhou, X., Sun, L.J.: Study on spectral characteristics of dissolved organic matter (DOM) from biochar [J]. J. Ecol. Rural Environ. 39 (06), 819–826 (2023). https://doi.org/10.19741/j.issn.1673-4831.2021.0775 Wang, Z.Q.C.D.: Difference analysis of material structure evolution time series of dissolved organic matter and humic acid during composting of different materials [J]. J. Environ. Eng. Technol. 13 (04), 1514–1524 (2023). https://doi.org/10.12153/j.issn.1674-991X.20221230 Wang, Z.M.L.Z., Liao, Y., Zhou, H.Y.Z.: Phage lysate can regulate the humification process of composting. Waste Manage. 178 , 221–230 (2024). https://doi.org/10.1016/j.wasman.2024.02.039 Cite Share Download PDF Status: Published Journal Publication published 20 Dec, 2025 Read the published version in Waste and Biomass Valorization → Version 1 posted Reviewers agreed at journal 11 Aug, 2025 Reviewers invited by journal 27 Jul, 2025 Editor invited by journal 19 Jul, 2025 Editor assigned by journal 01 Jul, 2025 First submitted to journal 27 Jun, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6995195","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":491528129,"identity":"67c48f77-04e9-40dd-8aaf-60aa3a1da576","order_by":0,"name":"Yongjian Liu","email":"","orcid":"","institution":"Inner Mongolia University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Yongjian","middleName":"","lastName":"Liu","suffix":""},{"id":491528130,"identity":"22b86744-8ca1-493b-a1fa-e97821b3c747","order_by":1,"name":"Jun Li","email":"","orcid":"","institution":"Inner Mongolia University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Jun","middleName":"","lastName":"Li","suffix":""},{"id":491528131,"identity":"66c39dde-1473-40fe-8c84-72888830c0b1","order_by":2,"name":"Limin Yuan","email":"","orcid":"","institution":"Inner Mongolia Academy of Forestry","correspondingAuthor":false,"prefix":"","firstName":"Limin","middleName":"","lastName":"Yuan","suffix":""},{"id":491528132,"identity":"db45a4ee-43ee-489a-a72a-0bc10754b57b","order_by":3,"name":"Zhao Yang","email":"","orcid":"","institution":"Inner Mongolia Academy of Forestry","correspondingAuthor":false,"prefix":"","firstName":"Zhao","middleName":"","lastName":"Yang","suffix":""},{"id":491528133,"identity":"eac48619-02de-417d-a226-756c29e71f8b","order_by":4,"name":"Litong Ma","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAtElEQVRIiWNgGAWjYDACdgaGAx8MbOTY2JsPEKmFmZnx4YyCNGM+nmMJRGthNub5cChxnkSOAnE6dJv5j0nzGBxIb2PIYWD4UbGNsBazw8xsknMM7uS2MZw9wNhz5jZxWiTeGDzLbWPsS2BmbCNWC4/B4XQ2Zh4DorUwGwK1JLCxkaDF8OEMgzTDNh62hIPE+eV444MDH/7YyMvPf3zwwY8KIrSggAMkqh8Fo2AUjIJRgAsAAAuFOl51xkyQAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-9850-2601","institution":"Inner Mongolia University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Litong","middleName":"","lastName":"Ma","suffix":""}],"badges":[],"createdAt":"2025-06-28 03:30:57","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6995195/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6995195/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12649-025-03452-4","type":"published","date":"2025-12-20T15:57:58+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":88090744,"identity":"d058b3a7-09dc-456a-a974-8d6ddc126c3a","added_by":"auto","created_at":"2025-08-01 10:14:51","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":252445,"visible":true,"origin":"","legend":"\u003cp\u003eUV-Visible spectrum SUVA\u003csub\u003e254\u003c/sub\u003e of DOM compost of sheep manure added to weathered coal in different proportions\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6995195/v1/bde9624aa8fd1a7c4d9e14c6.png"},{"id":88090739,"identity":"f7d9c835-bd24-4fa7-893b-42278993cada","added_by":"auto","created_at":"2025-08-01 10:14:50","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":266335,"visible":true,"origin":"","legend":"\u003cp\u003eUV-Visible spectrum E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e of DOM compost of sheep manure added to weathered coal in different proportions\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6995195/v1/86f7c08fc54e6005cfbb5f8f.png"},{"id":88093416,"identity":"1c8a33de-b32a-4a3c-8595-8d54cfceae3a","added_by":"auto","created_at":"2025-08-01 10:38:51","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":143930,"visible":true,"origin":"","legend":"\u003cp\u003eSynchronous scanning fluorescence spectra of sheep manure compost DOM in different proportions of weathered coal\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6995195/v1/1593fac8b8252df8eb4494b7.png"},{"id":88090740,"identity":"118ca6d5-1504-4466-91d0-7c3d6e6d4c50","added_by":"auto","created_at":"2025-08-01 10:14:51","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":225823,"visible":true,"origin":"","legend":"\u003cp\u003eA\u003csub\u003eHLR\u003c/sub\u003e/A\u003csub\u003eFLR \u003c/sub\u003eparameters of fluorescence spectra of sheep manure compost with DOM scanning in different proportions of weathered coal\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6995195/v1/a53b1e1fd10bc9a691d92305.png"},{"id":88092186,"identity":"4a2434cc-550f-402e-b584-42e195c00554","added_by":"auto","created_at":"2025-08-01 10:30:51","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":971338,"visible":true,"origin":"","legend":"\u003cp\u003eThree-dimensional fluorescence spectra of different proportions of weathered coal and sheep manure compost DOM\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6995195/v1/abde334408fac0f275fa90bb.png"},{"id":88090748,"identity":"d13778fe-d1d6-4954-a71a-02fae6a3941c","added_by":"auto","created_at":"2025-08-01 10:14:51","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":299380,"visible":true,"origin":"","legend":"\u003cp\u003eInfrared spectra of different proportions of weathered coal and sheep manure compost DOM\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-6995195/v1/8887dca74c3b5aa93702f635.png"},{"id":88091127,"identity":"e9887f19-7c21-49ea-bee8-ad4ffa7833ca","added_by":"auto","created_at":"2025-08-01 10:22:51","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":242964,"visible":true,"origin":"","legend":"\u003cp\u003eChanges of conductivity of DOM composted with sheep manure in different proportions of weathered coal\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-6995195/v1/4c1d11e7e8f8b71b2ab02e22.png"},{"id":88092188,"identity":"0eb164d8-1a9e-47f8-b5be-e99c417ee598","added_by":"auto","created_at":"2025-08-01 10:30:51","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":246065,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in pH value of DOM composted with sheep manure added from different proportions of weathered coal\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-6995195/v1/b9efffdbed899a669ae4b2e8.png"},{"id":98814114,"identity":"fa733f6f-638d-407b-9863-b1aaa195d22f","added_by":"auto","created_at":"2025-12-22 16:11:12","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3567848,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6995195/v1/484be63b-ef5b-490d-9639-13739db88c1c.pdf"}],"financialInterests":"","formattedTitle":"Effect of weathered coal on spectral changes of dissolved organic matter during sheep manure composting","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eIn recent years, with the rapid development of sheep farming, the discharge of large amounts of sheep manure has caused serious environmental pollution (Cai et al., 2023). Aerobic composting is the primary method used to manage sheep manure (Li et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Sheep manure is transformed into high-quality organic fertilizer through composting, reducing the pollution caused by sheep manure accumulation in the surrounding environment (Cai et al., 2024), improving its utilization rate, and increasing soil fertility. During aerobic composting of sheep manure, it is usually necessary to add high-carbon materials to adjust the carbon-to-nitrogen ratio and porosity of the organic fertilizer, which can promote the degradation of organic matter and improve the quality of the compost (Liu et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In recent years, dissolved organic matter (DOM) in sheep manure composting has been characterized to investigate the structural evolution and degree of humification of organic matter. DOM is a macromolecular organic mixture with a complex structure produced after the humification of organic matter in sheep manure. It is a variable component of organic matter in organic fertilizers, and its structural characteristics change as the compost stabilizes (Wang et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Yang et al. (2024) used three-dimensional fluorescence spectroscopy to demonstrate that the DOM treatment of low-concentration mature chicken manure compost reduced the bioavailability and migration risk of lead in soil, while increasing microbial abundance and diversity. These changes were more conducive to protecting the normal ecological function of soil. Song et al. (2023) used ultraviolet-visible absorption spectroscopy (UV-Vis) and three-dimensional fluorescence spectroscopy to demonstrate that biochar and montmorillonite can promote humification in chicken manure compost, improving both humification efficiency and carbon fixation during the composting process. Kong et al. (2023) used X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) to detect DOM evolution in the composting process of chicken and pig manure. The study revealed that struvite, calcite, and other crystal structure substances, cellulose, protein, carbohydrates, and microbial byproducts gradually decomposed, while humic acid content gradually increased during the process. The evolution of DOM is related to changes in the physical and chemical environments of compost. The maturity of compost can be observed through the content of humic acid, protein, carbohydrate, degree of aromatization in DOM, and crystal structure of the compost solid phase. Ma et al. (2024) added shell powder to cow manure for composting. The powder reduced CH\u003csub\u003e4\u003c/sub\u003e and CO emissions, and increased carbon fixation during composting, and significantly improved compost quality.\u003c/p\u003e\u003cp\u003eWeathering coal refers to a type of mineral resource formed by the long-term weathering of lignite, bituminous coal, and anthracite, either exposed to the surface or located in the shallow layers of the surface (Ma et al., 2024). The chemical composition and physical and chemical properties of weathered coal are different from those of raw coal. For example, its carbon and hydrogen content is low, while it contains more oxygen-containing acidic functional groups. The organic matter content in weathered coal can reach 40\u0026ndash;80%, most of which is recycled humic acid (Wang et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The humic acid in weathered coal has a larger cation exchange capacity, a more porous structure, and more active functional groups (Zhang et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). These characteristics enable weathered coal to exchange, chelate, and absorb nutrients in soil and fertilizer, allowing it to be more easily degraded by soil microorganisms (Zhang et al., 2017).\u003c/p\u003e\u003cp\u003eIn this study, sheep manure was used as the raw material, with the addition of weathered coal. The changes in DOM during the composting process were measured using UV-Vis spectroscopy, fluorescence spectroscopy, FTIR, 3D-EEM, pH, and conductivity analysis. The study examined the influence of weathered coal on the composting process of sheep manure and analyzed the structural evolution of organic matter and the degree of humification in organic fertilizers. This study aimed to provide a theoretical basis for the comprehensive collaborative utilization of aquaculture waste and low-quality coal resources.\u003c/p\u003e"},{"header":"2. Experimental methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Sheep manure compost and DOM preparation\u003c/h2\u003e\u003cp\u003eThe weathered coal was obtained from Xinjiang Qinghua Energy Group Co. Ltd. and sheep manure from a farm in Machi Town, Baotou City, Inner Mongolia. Fermentation of organic fertilizer was conducted in a vegetable greenhouse in Machi Town, Baotou City, Inner Mongolia. Different proportions of weathered coal and sheep manure were evenly mixed for composting and fermentation: 0% weathered coal with 100% sheep manure, 10% weathered coal with 90% sheep manure, and 15% weathered coal with 85% sheep manure. The compost made from pure sheep manure (0% weathered coal) served as the control group. The fermentation process lasted for 15 days, with the compost pile turned every 3 days. Fertilizer samples of sheep manure compost were collected as the raw material for DOM extraction.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Extraction of DOM\u003c/h2\u003e\u003cp\u003eFreshly acquired samples of sheep manure compost were weighed according to the dry matter weight of organic fertilizer; the volume of double steaming water is 1:10 (W (g)/V(mL)). The mixture was oscillated in a culture oscillation chamber at 200 r\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 27 ℃ for 16 h, followed by centrifugation at 8000 rpm at 4 ℃ for 30 min. The supernatant was collected and filtered through a 0.45 \u0026micro;m filter membrane to obtain the DOM as filtrate. The total organic carbon (TOC) content of the DOM in the fertilizer sample was determined using TOC-L CPH. The sample concentration was adjusted to 100 mg(C)\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with double distilled water. Double-distilled water was used as blank.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Spectral analyses\u003c/h2\u003e\u003cp\u003eFor UV-Vis spectral analysis, the DOM concentration of the fertilizer sample was adjusted to 100 mg(C)\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. A UV-Vis spectrophotometer was used to measure the absorbance of the compost sample daily over a scanning wavelength range of 200\u0026ndash;700 nm.\u003c/p\u003e\u003cp\u003eFor fluorescence spectral analysis, both emission and excitation monochromators were set to a scanning speed of 1200 nm\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, with a slit width of 5 nm. The fluorescence emission spectrum had a scanning range of 370\u0026ndash;600 nm and a fixed excitation wavelength of 350 nm. The excitation spectrum used a fixed emission wavelength of 560 nm and the excitation spectral scanning range was 300\u0026ndash;550 nm. Synchronous scanning excitation spectra ranged from 300\u0026ndash;600 nm, with a photomultiplier spectral width (Δλ) of 18 nm and voltage of 700 V. The instrument used was an F-2700 molecular fluorescence spectrometer (HITACHI, Tokyo, Japan). The concentration of DOM in the fertilizer sample was 100 mg(C)\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eFor FTIR analysis, 1 mg of freeze-dried DOM and 100 mg of chromatographically pure potassium bromide were finely ground, mixed, and pressed into thin slices. The infrared spectrum of the sample was measured and recorded using a FTIR spectrometer.\u003c/p\u003e\u003cp\u003e3D-EEM fluorescence spectroscopy characteristics of DOM (100 mg(C)\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) of compost samples were determined using a fluorescence spectrophotometer. The sample was placed in a 10 mm quartz colorimetric dish, with ultrapure water as the blank. The excitation wavelength (Ex) was scanned from 200\u0026ndash;600 nm in 10 nm intervals, and the emission wavelength (Em) was scanned from 220\u0026ndash;600 nm in 5 nm intervals, with a scanning speed of 48000 nm\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The photomultiplier tube gain was set to 650 V, and the response time was automatically matched.\u003c/p\u003e\u003cp\u003eFinally, pH and conductivity were determined for the initial DOM that had not been adjusted by concentration using a pH meter and a conductivity meter.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e3.1. UV-Vis spectrum analysis of DOM in sheep manure composting with weathering coal\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe specific ultraviolet absorbance at 254 nm (SUVA\u003csub\u003e254\u003c/sub\u003e) was defined as a ratio of 100 times the absorbance of the DOM in organic fertilizer at 254 nm to the TOC of the DOM solution. Yang et al. (2024) suggested that the UV absorption of organic matter at 254 nm mainly represents compounds with unsaturated carbon-carbon bonds, such as aromatic compounds. At 254 nm, the increase in the light absorption value indicates the conversion of non-humic organic matter to humus with the same DOM concentration (Liu et al., 2023), further indicating an increased degree of decomposition of compost. The UV absorption intensity of DOM in sheep manure compost at 254 nm in the absence and presence of 10% or 15% weathered coal are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. In the absence of weathered coal a decrease in absorbance from 0.173 to 0.101 was followed by an increase to 0.162. In the presence of 10% weathered coal, the absorbance decreased from 0.210 at the beginning of composting to 0.138 and finally increased to 0.177. In the presence of 15% weathered coal, the absorbance increased from 0.177 at the beginning of composting and finally increased to 0.734. The results showed that macromolecular substances, such as humic acid, cellulose, hemicellulose, lignin, and proteins, contained in the DOM during the early fermentation stage were gradually degraded by the microorganisms. At 254 nm, the absorbance of DOM increased and the amino acid and lignin degradation products continued to condense to form humic acids. The humus of sheep manure organic fertilizer continued to increase, and the degree of humification increased with the fermentation of the fertilizer (Zhang et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The absorbance value at 254 nm of 0.734 in the presence of 15% weathered coal manure compost was higher than that of 0.177 in the presence of 10% weathered coal and 0.162 in the absence of weathered coal. The increased absorbance values indicated that organic non-humus with the same DOM concentration continuously condensed into humus and increased compost maturation (Danil et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The findings indicate that the addition of weathered coal promoted an increase in humic acid in the sheep manure compost, and the addition of 15% weathered coal compost promoted the humification of sheep manure compost.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.2. E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e analysis of DOM in sheep manure composting by weathering coal\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eUV-Vis light absorbances at 465 and 665 nm were defined as E\u003csub\u003e4\u003c/sub\u003e and E\u003csub\u003e6\u003c/sub\u003e (Lan et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), respectively. E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e is the ratio of the absorbance of DOM at 465 and 665 nm. This ratio is often used to characterize the stability of organic matter in the composting process. The smaller the value of E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e, the greater the complexity of macromolecular organic matter (Zhou et al., 2023), that is, the greater the degree of polymerization of organic matter. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e of the UV-Vis spectrum of DOM in sheep manure compost with 10% or 15% weathered coal.\u003c/p\u003e\u003cp\u003eThe E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e value of the sheep manure compost with the addition of weathered coal gradually increased to its highest value at the beginning of composting, indicating that the DOM of the compost sample decreased convertible organic matter, such as lignin and cellulose, in the sheep manure during the fermentation process. The macromolecular matter decomposed, the degree of polymerization of organic matter decreased, and then the E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e value decreased at the end of the organic fertilizer fermentation. After decomposition, pyruvate, amino acids, and other small molecules of organic matter begin to polymerize, and the continuous synthesis of humic acid substances increases the degree of organic matter polymerization (Dong et al., 2024).\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e value of sheep manure compost without weathered coal increased from 6.222 at the beginning of composting to 6.647 at the end. The DOM of the sheep manure organic fertilizer with 10% weathered coal increased the degree of product polymerization from the beginning to the end of composting. The value of E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e decreased from 5.444 at the beginning to 5.121 at the end of the composting process, indicating that large molecules, such as cellulose, lignin, and protein, first decomposed to form smaller organic compounds that included pyruvate and amino acids. As composting progressed, humic acids were synthesized, which increased the degree of polymerization of organic matter. The DOM of sheep manure organic fertilizer amended with 15% weathered coal showed a decrease in the degree of polymerization from the beginning to the end of composting, similar to that of sheep manure compost without weathered coal. The E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e value increased from 4.322 at the beginning to 4.608 at the end of composting. However, the E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e value was the lowest at the beginning of composting. The results showed that sheep manure organic fertilizer with 15% weathered coal initially contained more macromolecular organic matter, and during the composting process, the macromolecular organic matter decomposed first to form small molecular organic matter. As composting progressed, humic acid substances began to be synthesized, and the degree of polymerization of the organic matter increased. The addition of weathered coal increased the degree of organic matter polymerization and humification in the sheep manure compost. At the end of composting, the E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e value of 4.608 for sheep manure organic fertilizer with 15% weathered coal was lower than 5.121 of the organic fertilizer with 10% weathered coal, indicating that the organic matter of sheep manure organic fertilizer with 15% weathered coal had a greater degree of polymerization and compost humification, further indicating that the degree of compost decomposition increased.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.3. Fluorescence spectrum characteristics of DOM in sheep manure composting in the presence of weathering coal\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea shows the synchronous scanning fluorescence spectrum for 0% weathered coal, whereas Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and c display the spectra for 10% and 15% weathered coal added to sheep manure compost, respectively. The spectra indicate that different DOM components have different absorption intensities at different wavelengths, and this method is commonly used to characterize the degree of humification in compost (Marta et al., 2024). In the spectra of sheep manure compost with weathered coal (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and c), the DOM of the compost showed distinct fluorescence peaks at 360\u0026ndash;390, 430\u0026ndash;450, and 460\u0026ndash;490 nm. However, in the spectrum of compost without weathered coal (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea), the DOM showed fluorescence peaks at 360\u0026ndash;390 and 430\u0026ndash;450 nm, closely aligning with the characteristic peaks of soil fulvic acid (330\u0026ndash;360, 390\u0026ndash;430, and 460\u0026ndash;490 nm) (Zhao et al., 2023). This suggests that the humic substances in DOM were mainly fulvic acids. As the proportion of aromatic structures in the humic substances increases, a redshift in the spectrum peak occurs (Wu et al., 2023).\u003c/p\u003e\u003cp\u003eAccording to Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and c, the maximum peaks of the three humic peaks (380, 430, and 475 nm) in the fluorescence spectra of the sheep manure compost DOM with the addition of weathered coal moved in the long wave direction and the peaks shifted to the right at 383, 432, and 478 nm, respectively, from the beginning of day 0 to the end of day 15. The fluorescence peak of sheep manure compost DOM in the absence of weathered coal also showed a similar shift. The shift was more pronounced in compost with added weathered coal than in the compost without weathered coal, indicating the presence of thick cyclic aromatic hydrocarbons in the DOM of compost with added weathered coal, resulting in a shift in the maximum fluorescence peak position. This shows that the addition of weathered coal can increase the benzene ring structure of organic matter during composting, increase the degree of conjugation, and improve the stability of the final product (Wang et al., 2021).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe DOM synchronous scanning fluorescence spectra, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, reveal two regions: Region A (330\u0026ndash;360, 390\u0026ndash;430, and 460\u0026ndash;490 nm) represented the fulvic acid fluorescent region (FLR) associated with dense aromatic hydrocarbons with 3\u0026ndash;4 benzene rings in fulvic acids. Region B (490\u0026ndash;595 nm) is the humic acid fluorescent region (HLR) related to polycyclic aromatic structures of dense aromatic hydrocarbons with 5\u0026ndash;7 benzene rings in humic acids (Dong et al., 2019). The fluorescence regions of A\u003csub\u003eFLR\u003c/sub\u003e and A\u003csub\u003eHLR\u003c/sub\u003e correspond to the proportion of the fluorescence integral area to the total area in the range of 300\u0026ndash;460 and 460\u0026ndash;600 nm, respectively.\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the A\u003csub\u003eFLR\u003c/sub\u003e values decreased, while the A\u003csub\u003eHLR\u003c/sub\u003e values increased. The contents of fulvic acids decreased and humic acids increased in DOM components during composting. Because the different components of DOM change during composting, the spectrum moves in the direction of the long wave. The ratio of the A\u003csub\u003eHLR\u003c/sub\u003e area to the A\u003csub\u003eFLR\u003c/sub\u003e area (A\u003csub\u003eHLR\u003c/sub\u003e/A\u003csub\u003eFLR\u003c/sub\u003e) was used to reveal the conversion of DOM during composting (Li et al., 2023). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, A\u003csub\u003eHLR\u003c/sub\u003e/A\u003csub\u003eFLR\u003c/sub\u003e continued to increase overall. The A\u003csub\u003eHLR\u003c/sub\u003e/A\u003csub\u003eFLR\u003c/sub\u003e ratio of the DOM of composting sheep manure increased from 0.1404 at the beginning to 0.1465 at the end of composting. The A\u003csub\u003eHLR\u003c/sub\u003e/A\u003csub\u003eFLR\u003c/sub\u003e of DOM of composting sheep manure in the presence of 10% weathered coal increased from 0.4156 at the beginning to 0.4366 at the end of composting. A\u003csub\u003eHLR\u003c/sub\u003e/A\u003csub\u003eFLR\u003c/sub\u003e increased from 0.4732 at the beginning of composting to 0.6299 at the end of composting, indicating that the aromatic structure of humic increased over time, with the final product of composting tending to be stable. The addition of weathered coal was helpful for the decomposition of the sheep manure compost, and the addition of 15% weathered coal was better at promoting the humification of composting sheep manure.\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the A\u003csub\u003eHLR\u003c/sub\u003e/A\u003csub\u003eFLR\u003c/sub\u003e ratio changed, generally in an upward trend. Sheep manure devoid of and amended with 10% weathered coal showed a maximum peak value on day 12; at that time more humic acid was produced by the fermentation reaction than fulvic acid. The A\u003csub\u003eHLR\u003c/sub\u003e/A\u003csub\u003eFLR\u003c/sub\u003e ratio was reduced, but still greater than that at the beginning of composting, indicating that a part of the humic acid was converted to fulvic acid during the composting process. The peak of sheep manure with 15% weathered coal appeared earlier than the peak in the other two groups, indicating that 15% weathered coal could accelerate the composting process.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.4. Influence of weathered coal on three-dimensional fluorescence spectrum characteristics of DOM during sheep manure composting\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eHumic acid in DOM, produced during the composting process, contains benzene ring structures that absorb the excitation light of certain energies. Therefore, a three-dimensional fluorescence spectrum can be used to analyze the evolution of DOM during the composting process (Wei et al., 2022).\u003c/p\u003e\u003cp\u003eThe three-dimensional fluorescence spectra of water-soluble organic compounds were analyzed using the region integral method. The spectra were divided into five regions. Region I (Ex: 220\u0026ndash;250 nm, Em: 290\u0026ndash;330 nm) and Region II (Ex: 220\u0026ndash;250 nm, Em: 330\u0026ndash;380 nm) correspond to protein fluorescence in the aromatic compounds. Region III (Ex: 220\u0026ndash;250 nm, Em: 380\u0026ndash;500 nm) represents the fulvic acid-like fluorescence region. Region IV (Ex: 250\u0026ndash;400 nm, Em: 290\u0026ndash;380 nm) defines the dissolved microbial byproduct fluorescence. Region V (Ex: 250\u0026ndash;400 nm, Em: 380\u0026ndash;500 nm) is associated with humic acid fluorescence (Lu et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe absorption intensities of different water-soluble organic compounds in the DOM of sheep manure amended with weathered coal differed at different excitation and emission wavelengths. Figures\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e show the three-dimensional fluorescence spectra of DOM during composting with 0% (a-f), 10% (h-m), and 15% (n-s) weathered coal, respectively. Panels a\u0026ndash;f in these figures represent the spectra of DOM at 0, 3, 6, 9, 12, and 15 days of composting, respectively. During composting, the fluorescence peak of DOM was approximately Ex/Em\u0026thinsp;=\u0026thinsp;400 nm/450 nm (Lu et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Liu et al. (2023) reported that the main source of this fluorescence peak was fulvic acid, which is a water-soluble humic acid. As composting time increased, the intensity of the fluorescence peak first decreased from day 0 to day 3, followed by gradual increases. The fluorescence peaks shifted towards larger emission and excitation wavelengths.\u003c/p\u003e\u003cp\u003eAs shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the three-dimensional fluorescence spectra of DOM in sheep manure composting, with added weathered coal, and the main peak area of DOM in the sheep manure composting process with the addition of 0% weathered coal was in Region V, indicating that the content of humic acids mainly changed in the composting process (Zhao et al., 2024). The fluorescence peaks of DOM with different proportions of weathered coal showed the same trend: first decreasing and then increasing as composting progressed, with reaching a peak on day 15. This was due to the formation of humic acids under the action of microorganisms. As easily degradable organic matter (hemicellulose, cellulose, and protein) in the compost was consumed, microorganisms began degrading the refractory organic matter, such as lignin. Simultaneously, the previously generated humic acids further transformed into high molecular weight and more stable humic substances, resulting in a continuous increase in humic content and the degree of humification in the compost. Moreover, the observed redshift in the fluorescence peak in the DOM three-dimensional fluorescence spectrum may have been related to the increase in carbonyl, hydroxyl, alkoxy, amino, and carboxylic groups, indicating that the molecular weight, aromatics, and hydrophobicity of DOM increased with the deepening of humification in the compost (Wang et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In the early stages of composting, the high fluorescence peak was due to the high humic acid content in the weathered coal. Subsequently, decomposition occurred under the action of microorganisms, which reduced the content of humic acid. As the composting days increased, the composition of DOM changed, and its structure transformed into more complex humic acids. Thus, in the composting process, the structure of simple small subclasses of substances continues to decrease, and the structure of complex macromolecular substances continues to increase. At the end of composting, the peak fluorescence of sheep manure organic fertilizer amended with 15% weathered coal was 357.8. This value was higher than the value of 303.7 for sheep manure organic fertilizer amended with 10% weathered coal. Both values exceeded the peak of 287.2 observed in the absence of weathered coal. The results indicate that more humic acids were present in sheep manure organic fertilizer amended with 15% weathered coal, indicating a greater degree of humification. The addition of weathered coal promotes the maturation of sheep manure compost.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.5. Influence of weathered coal on the infrared spectral characteristics of DOM during sheep manure composting\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea displays the infrared spectrum of DOM of sheep manure compost in the absence of weathered coal. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eb and c show the infrared spectra of the DOM of sheep manure compost in the presence of 10% and 15% weathered coal, respectively. In panels b and c, four prominent absorption peaks are present at approximately 3420, 1630, 1385, and 1100 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the infrared spectrum of the DOM. In the control group (spectrum a), similar infrared absorption peaks were present but with low intensity. In addition, several smaller absorption peaks in the range of 500\u0026ndash;750 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were evident. The absorption peaks in the 3500\u0026ndash;3000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e range correspond to the stretching vibrations of -OH in -COOH, alcohol, and phenol. The peaks at 1660\u0026ndash;1600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e may reflect the stretching vibrations of olefin-C\u0026thinsp;=\u0026thinsp;C-, carbonyl (-C\u0026thinsp;=\u0026thinsp;O) groups in carboxylic acid, or -C\u0026thinsp;=\u0026thinsp;O in the associated amides (Wang et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The peaks at 1420\u0026ndash;1300 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e may be part of the characteristic spectrum of humic materials, reflecting symmetric stretching vibrations of -COO-, -C-O-H curved band, or bonded aromatic ring class. The peaks at 830\u0026ndash;820 and 671 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are the characteristics of aromatic rings. The 603 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e peak is the N-H bending band of an amino compound (Yang et al., 2020). The absorption peaks in the ranges 3500\u0026ndash;3000 and 1660\u0026ndash;1600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e indicate that the DOM contains a benzene ring and phenolic functional groups. The presence of absorption peaks at 3500\u0026ndash;3000, 1660\u0026ndash;1600, and 1420\u0026ndash;1300 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e indicates the presence of -COOH in the compost sample. The absorption spectra displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e indicate that while the same functional groups are present in the compost DOM, the contents of some functional groups are different. The increase in the relative intensity of the absorption peak (i.e., the peak value) indicates an increased content of the functional group corresponding to the absorption peak (Guo et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). As compost fermentation progressed, the relative intensity (i.e., peak value) of the DOM absorption peak in the 3500\u0026ndash;3000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e range generally decreased from day 0 to day 15, indicating that cellulose, hemicellulose, and protein decomposition in the compost raw materials reduced hydroxyl and methyl groups. However, fluctuations were observed during the composting process, with the relative intensity of the absorption peak of all compost DOM at 1300 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increasing from day 0 to day 15, indicating an increase in humic substances. Moreover, the intensity of the infrared absorption peak of DOM in sheep manure compost with 15% weathered coal was higher than that of DOM in sheep manure compost with 10% weathered coal, indicating a greater degree of humification in the compost with 15% weathered coal. This suggests that the addition of weathered coal positively affected the fermentation process of sheep manure compost. At the absorption peak in the 600\u0026ndash;800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e range, the absorption intensity of sheep manure compost with weathered coal was significantly higher than that of compost without weathered coal, indicating that the addition of weathered coal promoted the formation of more stable humic acid aromatic compounds during the composting process.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.6. Influence of weathered coal on the conductivity of DOM during sheep manure composting\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe conductivity of DOM during composting reflects the content of soluble salts (both organic and inorganic) present. The high salt content can be detrimental to plant growth, leading to land salinization, water loss in plants, and reduced survival rates. Conversely, too low a salt content indicates insufficient nutrients, which can also affect plant growth (Xiao et al., 2022).\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows the change in DOM conductivity during the composting process with the addition of weathered coal. On day 0 of composting, the conductivity was low due to the presence of more macromolecular organic materials in the raw composting materials. As composting progressed, these macromolecular substances\u0026mdash;such as humic acid, cellulose, hemicellulose, lignin, and proteins\u0026mdash;were decomposed into smaller molecular substances, including water-soluble humic acid, pyruvate, amino acids, and some soluble salts. With the progress of composting, soluble salts were utilized by microorganisms, and some soluble substances were transformed into relatively stable macromolecular organic compounds such as humic acid. Consequently, the electrical conductivity gradually decreased and stabilized (Sun et al., 2023). This trend indicates a reduction in the content of soluble salts (Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e), an increase in humic acids, and an overall increase in the degree of humification during the composting process (Wang et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). The average conductivity of sheep manure organic fertilizer with 15% weathered coal was lower than that of the fertilizer with 10% weathered coal, indicating that the addition of 15% weathered coal facilitated the synthesis of humic acids and reduced soluble salt content, thereby improving the fermentation effect of compost compared with the 10% weathered coal treatment. The conductivity of the DOM in sheep manure compost in the absence of weathered coal was lower than that in the presence of weathered coal, further indicating that the addition of weathered coal promoted the synthesis of humic acid and reduced soluble salt content in sheep manure.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.7. Influence of weathered coal on the pH of DOM during sheep manure composting\u003c/h2\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eDuring composting, the life activities of microorganisms essentially depend on the appropriate pH, as both excessively high and low values can hinder microbial reproduction and the degradation of organic matter in the compost material. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows how the pH value of DOM in sheep manure compost changes over time with different proportions of weathered coal. The pH of the DOM in the presence of weathered coal generally increased initially and then decreased; however, the presence of easily decomposable ammoniated nitrogen-containing organic matter caused fluctuations in pH. During the early stages of composting, pH first increased to 7.73 and 7.55, respectively, before decreasing to 7.42 and 7.38 by the end of the composting period, remaining within the weakly alkaline range. The initial increase in pH value can be attributed to the production of ammonia from nitrogen-containing compounds in the pile during ammonification, which could not be released into the air in time and remained in the pile. Subsequently, ammonia reacted with water in the compost, generating a trace amount of ammonia, which was transferred to the DOM of the compost, resulting in an increased pH of the DOM (Balasubramani et al., 2022). The pH decreased slightly after day 6 due to the accumulation of organic acids, such as water-soluble humic acid, propionic acid, pyruvic acid, and other carboxylic acids, which resulted from organic degradation, and did not decompose over time. As the compost continued to decompose, humic acids and other substances accumulated in the heap, causing the pH of the compost DOM to become weakly alkaline. Compared with the compost with 10% and 0% weathered coal, the pH value of the DOM in sheep manure compost with 15% weathered coal was consistently lower, not exceeding 7.40. This was lower than the pH values of 7.42 and 7.60 for the DOM in sheep manure compost with 10% and 0% weathered coal, respectively, indicating that more acidic humic acids were generated in the DOM.\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThe addition of weathered coal significantly affected the DOM during sheep manure composting, and the degree of humification of the compost increased, indicating an increase in the degree of decomposition of the compost. UV-Vis spectrogram analysis revealed that when 15% of weathered coal was added, the absorbance value at 254 nm increased to 0.734, which is higher than the absorbance values of 0.177 for the compost with 10% weathered coal and 0.162 for the compost without weathered coal. The increase in the absorbance value indicated that non-humic organic matter with the same DOM concentration was continuously condensed into humus, showing increased compost maturation. The addition of weathered coal promoted an increase in humic acid in sheep manure compost, with the 15% weathered coal promoting humification. At the end of composting, the E\u003csub\u003e4\u003c/sub\u003e/E\u003csub\u003e6\u003c/sub\u003e ratio for sheep manure organic fertilizer with 15% weathered coal was 4.608, lower than the 5.121 for fertilizer with 10% weathered coal, indicating that the organic matter in sheep manure organic fertilizer with 15% weathered coal exhibited a greater degree of polymerization and humification in the compost, suggesting an increase in the degree of decomposition of the compost.\u003c/p\u003e\u003cp\u003eFluorescence spectra analysis showed that the addition of weathered coal increased the humus in sheep manure compost, the benzene ring structure of organic matter, conjugation degree, maturity, and stability of the compost fertilizer. Additionally, a portion of humic acid was converted into fulvic acid during composting, and the addition of 15% weathered coal accelerated this process.\u003c/p\u003e\u003cp\u003eAnalysis of three-dimensional fluorescence spectra demonstrated that at the end of composting, the fluorescence peak of sheep manure organic fertilizer with 15% weathered coal reached 357.8, higher than 303.7 for the fertilizer with 10% weathered coal, and both were larger than 287.2 for the 100% sheep manure organic fertilizer. This indicates more humic acids were present in the fertilizer with 15% weathered coal, suggesting greater humification of the compost. Therefore, the addition of weathered coal promotes the maturation of sheep manure.\u003c/p\u003e\u003cp\u003eAccording to the infrared spectrum analysis, the degree of humification in sheep manure compost with 15% weathered coal was high, indicating that weathered coal facilitated the fermentation process. At the absorption peak of 600\u0026ndash;800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the intensity for compost with weathered coal was significantly higher than that of the control group, indicating that the addition of weathered coal promoted the formation of more stable humic acid aromatic compounds in sheep manure compost during composting.\u003c/p\u003e\u003cp\u003eAnalyses of pH and conductivity showed that the addition of weathered coal was conducive to the synthesis of humic acid in DOM and reduced the soluble salt content in sheep manure.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData curation, and Writing-original draft, Yongjian Liu; Formal analysis, Jun Li; Data testing, Yang Zhao; Language polishing,\u0026nbsp;Limin Yuan;\u0026nbsp;Funding acquisition, Methodology, Litong Ma.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work is financially supported by the Inner Mongolia Autonomous Region Science and Technology Plan Project (2025KYPT0175).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMukesh, B.R.N.K., Soon, K.A., Selvi, W.C.P.K., Nur, R.B.S.C.: Ganesh. M. Valorization of food waste and poultry manure through co-composting amending saw dust, biochar and mineral salts for value-added compost production. Bioresour. Technol. \u003cb\u003e346\u003c/b\u003e, 126442 (2022). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.biortech.2021.126442\u003c/span\u003e\u003cspan address=\"10.1016/j.biortech.2021.126442\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCao, C.R.C.X., Jiang, X., Xu, X.W.R.: Crushing combined with high-frequency turning can promote material degradation of sheep manure compost on the Qinghai-Tibet Plateau by improving the microbial metabolic function. J. Environ. Chem. Eng. \u003cb\u003e11\u003c/b\u003e(2), 109535 (2023). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jece.2023.109535\u003c/span\u003e\u003cspan address=\"10.1016/j.jece.2023.109535\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eXu, C.R.L.R.C.X.: Available sulfur and phosphorus transformation mechanism and functional microorganisms during sheep manure composting on Qinghai-Tibet Plateau under two moisture contents. Bioresour. Technol. \u003cb\u003e394\u003c/b\u003e, 130191 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.biortech.2023.130191\u003c/span\u003e\u003cspan address=\"10.1016/j.biortech.2023.130191\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDanil, G., Kurashev, R.M., Manasypov, T.V., Raudina, I.V., Krickov, A.G., Lim, Oleg, S.: Pokrovsky. Dissolved organic matter quality in thermokarst lake water and sediments across a permafrost gradient. Western Siberia Environ. Res. \u003cb\u003e252\u003c/b\u003e, 119115 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.envres.2024.119115\u003c/span\u003e\u003cspan address=\"10.1016/j.envres.2024.119115\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWei, D.S.L.R.Z.K., Chen, Y.L.J.C.M.: Hu. X. Response of humification process to fungal inoculant in corn straw composting with two different kinds of nitrogen sources. Sci. Total Environ. \u003cb\u003e946\u003c/b\u003e, 174461 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scitotenv.2024.174461\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2024.174461\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang, D.L., Ma, X.: Effect of lignite addition on the characteristics of spectral changes of water-soluble organic matter during sheep manure organic fertilizer fermentation [J]. Spectrosc. Spectr. Anal. \u003cb\u003e39\u003c/b\u003e(11), 3579\u0026ndash;3584 (2019). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3964/j.issn.1000-0593(2019)11-3579-06\u003c/span\u003e\u003cspan address=\"10.3964/j.issn.1000-0593(2019)11-3579-06\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGuo, X., He, X., Li, C., Li, N.: The binding properties of copper and lead onto compost-derived DOM using Fourier-transform infrared, UV-Vis and fluorescence spectra combined with two-dimensional correlation analysis. J. Hazard. Mater. \u003cb\u003e365\u003c/b\u003e, 457\u0026ndash;466 (2019). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jhazmat.2018.11.035\u003c/span\u003e\u003cspan address=\"10.1016/j.jhazmat.2018.11.035\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKong, X., Yan, L.G.: Xie. G. Dissolved organic matter evolution can reflect the maturity of compost: Insight into common composting technology and material composition. J. Environ. Manage. \u003cb\u003e326\u003c/b\u003e(B), 116747 (2023). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jenvman.2022.116747\u003c/span\u003e\u003cspan address=\"10.1016/j.jenvman.2022.116747\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLi, Y., Liu, T.Q., Ding, S., Min, W.: Yuan. C. Effects of the combined compost of grape branches and sheep manure on a soil-microorganism-chardonnay (Vitis vinifera L.) plant ecosystem. Sci. Hort. \u003cb\u003e336\u003c/b\u003e, 113430 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scienta.2024.113430\u003c/span\u003e\u003cspan address=\"10.1016/j.scienta.2024.113430\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLiu, H., Mukesh, K.A., Asad, Z.Z.: Ali. H.B. Evaluation of gases emission and enzyme dynamics in sheep manure compost occupying with peach shell biochar. Environ. Pollut. \u003cb\u003e351\u003c/b\u003e, 124065 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.envpol.2024.124065\u003c/span\u003e\u003cspan address=\"10.1016/j.envpol.2024.124065\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBai, L.C., Zhao, X.: Effects of spring maize straw returning methods on soil DOM spectral characteristics in Cold and arid regions [J]. J. Ecol. Environ. \u003cb\u003e32\u003c/b\u003e(08), 1419\u0026ndash;1432 (2023). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.16258/j.cnki.1674-5906.2023.08.007\u003c/span\u003e\u003cspan address=\"10.16258/j.cnki.1674-5906.2023.08.007\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLan, J., Liu, L., Wang, X., et al.: DOM tracking and prediction of rural domestic sewage with UV\u0026ndash;vis and EEM in the Yangtze River Delta, China. \u003cb\u003e29\u003c/b\u003e, 74579\u0026ndash;74590. (2022). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11356-022-20979-4\u003c/span\u003e\u003cspan address=\"10.1007/s11356-022-20979-4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLi, H., Garrett., M.: Fluorescence Quenching of Humic Substances and Natural Organic Matter by Nitroxide Free Radicals. Environ. Sci. Technol. \u003cb\u003e57\u003c/b\u003e(1), 719\u0026ndash;729 (2023). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acs.est.2c02220\u003c/span\u003e\u003cspan address=\"10.1021/acs.est.2c02220\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLu, M., Hao, L.B.Z.Y., Li, Y., Huang, K., Li, Z.: Ji. Insight into the molecular transformation pathways of humic acid in the co-composting of bagasse and cow manure after adding compound microorganisms. Process Biochem. \u003cb\u003e143\u003c/b\u003e, 23\u0026ndash;33 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.procbio.2024.04.029\u003c/span\u003e\u003cspan address=\"10.1016/j.procbio.2024.04.029\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang, L.J., Bao, N.M.F., Hao, Z.W.J.: Wei. Y. Insights into the roles of DOM in humification during sludge composting: Comprehensive chemoinformatic analysis using FT-ICR mass spectrometry. Chem. Eng. J. \u003cb\u003e475\u003c/b\u003e, 146024 (2023). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cej.2023.146024\u003c/span\u003e\u003cspan address=\"10.1016/j.cej.2023.146024\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLi, M.L.: A new strategy to increase compost carbon fixation: Shell powder reduced gaseous pollutant emissions in co-composting of cow manure and sawdust. J. Environ. Chem. Eng. \u003cb\u003e12\u003c/b\u003e(3), 112916 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jece.2024.112916\u003c/span\u003e\u003cspan address=\"10.1016/j.jece.2024.112916\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLi, M.L., Liu, L.: Chem. Biol. Eng. \u003cb\u003e41\u003c/b\u003e(02), 7\u0026ndash;12 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3969/j.issn.1672-5425.2024.02.002\u003c/span\u003e\u003cspan address=\"10.3969/j.issn.1672-5425.2024.02.002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e Y. Research progress on extraction and application of humic acid from weathered coal [J]\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMarta, P.R., Llorent-Mart\u0026iacute;nez, A.D.E.J.: Mar\u0026iacute;a Jos\u0026eacute; Ayora-Ca\u0026ntilde;ada. Monitoring organic matter transformation of olive oil production residues in a full-scale composting plant by fluorescence spectroscopy. Environ. Technol. Innov. \u003cb\u003e35\u003c/b\u003e, 103695 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.eti.2024.103695\u003c/span\u003e\u003cspan address=\"10.1016/j.eti.2024.103695\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGao, S.C., Sun, Y., Zhao, Q., Qi, Y., Wang, H.C.Z.L.J.: Wei. Z. Insight into the pathways of biochar/smectite-induced humification during chicken manure composting. Sci. Total Environ. \u003cb\u003e905\u003c/b\u003e, 167298 (2023). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scitotenv.2023.167298\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2023.167298\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhu, S.H.C.S., Xie, N.P.J.W.J.: Feng. Ya. Hydrothermal carbonization aqueous phase promotes nutrient retention and humic substance formation during aerobic composting of chicken manure. Bioresour. Technol. \u003cb\u003e385\u003c/b\u003e, 129418 (2023). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.biortech.2023.129418\u003c/span\u003e\u003cspan address=\"10.1016/j.biortech.2023.129418\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang, W., Zhu, Y., Qu, J.: Effect of DOM derived from composting on the changes of Pb bioactivity in black soil. J. Environ. Chem. Eng. \u003cb\u003e12\u003c/b\u003e(2), 112232 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jece.2024.112232\u003c/span\u003e\u003cspan address=\"10.1016/j.jece.2024.112232\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang, K., Yang, Z.X.Z.J.Z.W.: Wang. X. Amended soils with weathered coal exhibited greater resistance to aggregate breakdown than those with biochar: From the viewpoint of soil internal forces. Soil Tillage. Res. \u003cb\u003e244\u003c/b\u003e, 106244 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.still.2024.106244\u003c/span\u003e\u003cspan address=\"10.1016/j.still.2024.106244\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWu, S., Sun, D.T.: Impact of compost methods on humification and heavy metal passivation during chicken manure composting. J. Environ. Manage. \u003cb\u003e325\u003c/b\u003e(B), 116573 (2023). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jenvman.2022.116573\u003c/span\u003e\u003cspan address=\"10.1016/j.jenvman.2022.116573\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRen, W.Q., Sun, X., Zhao, Y., Mukesh, J.: Zhang. Z. Improvement of the composition and humification of different animal manures by black soldier fly bioconversion. J. Clean. Prod. \u003cb\u003e278\u003c/b\u003e, 123397 (2021). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jclepro.2020.123397\u003c/span\u003e\u003cspan address=\"10.1016/j.jclepro.2020.123397\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eShen, W.J.S.H., Mi, C., Liu, H.: Zhou. S. Deciphering the structural characteristics and molecular transformation of dissolved organic matter during the electrolytic oxygen aerobic composting process. Sci. Total Environ. \u003cb\u003e845\u003c/b\u003e, 157174 (2022). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scitotenv.2022.157174\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2022.157174\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang, W., Zhu, Y., Qu, J.: Effect of DOM derived from composting on the changes of Pb bioactivity in black soil. J. Environ. Chem. Eng. \u003cb\u003e12\u003c/b\u003e(2), 112232 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jece.2024.112232\u003c/span\u003e\u003cspan address=\"10.1016/j.jece.2024.112232\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang, H., Li, G.X., Heyong, S., Huang: Insight into the binding characteristics of dissolved organic matter (DOM) and Fe(Ⅱ)/Mn(Ⅱ): Based on the spectroscopic and dialysis equilibrium analysis. Chemosphere. \u003cb\u003e362\u003c/b\u003e, 142672 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2024.142672\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2024.142672\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang, S., Cui, L.P.W.M., Tuo, Y., Zhao, Y.: Wang. N. Evaluation of chemical properties and humification process during co-composting of spent mushroom substrate (Pleurotus ostreatus) and pig manure under different mass ratios. Int. Biodeterior. Biodegrad. \u003cb\u003e193\u003c/b\u003e, 105858 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ibiod.2024.105858\u003c/span\u003e\u003cspan address=\"10.1016/j.ibiod.2024.105858\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLiu, X.J.W.G., Dai, H.: Application of composted lipstatin fermentation residue as organic fertilizer: Temporal changes in soil characteristics and bacterial community. Chemosphere. \u003cb\u003e306\u003c/b\u003e, 13563 (2022). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2022.135637\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2022.135637\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhu, Y.W., Jiang, Y., Jin, Y.Z.J.W.W., Liu, Y.: Qu. J. Dissolve organic matter of mature chicken compost contributes to the protection of microorganisms from the stress of heavy metals. J. Environ. Chem. Eng. \u003cb\u003e12\u003c/b\u003e(5), 113590 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jece.2024.113590\u003c/span\u003e\u003cspan address=\"10.1016/j.jece.2024.113590\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCui, Y.Y.D.W., Zhao, Z., Lv, T.W.X.: Spectroscopic characteristics of dissolved organic matter during pig manure composting with bean dregs and biochar amendments. Microchem. J. \u003cb\u003e158\u003c/b\u003e, 105226 (2020). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.microc.2020.105226\u003c/span\u003e\u003cspan address=\"10.1016/j.microc.2020.105226\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhang, X., Wang, Z.J.W.K., Xie, X.Z.Z.: Cai. J. Greater mineral and aggregate protection for organic carbon in the soil amended by weathered coal than by biochar: Based on a 3-year field experiment. Geoderma. \u003cb\u003e438\u003c/b\u003e, 116639 (2023). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.geoderma.2023.116639\u003c/span\u003e\u003cspan address=\"10.1016/j.geoderma.2023.116639\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLi, Z.S.Y.L., Lin, W., Li, Z., Hu, Y.: Zhao. B. Characterization of pH-fractionated humic acids derived from Chinese weathered coal. Chemosphere. \u003cb\u003e166\u003c/b\u003e, 334\u0026ndash;342 (2017). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2016.09.095\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2016.09.095\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhang, X., Zhu, C.F.Y.D., Zhang, Y.Z.Y.: Effects of wet-dry alternation on organic phosphorus dynamics and sediment characteristics in the intertidal zone of Nansi Lake. Ecotoxicol. Environ. Saf. \u003cb\u003e281\u003c/b\u003e, 116668 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ecoenv.2024.116668\u003c/span\u003e\u003cspan address=\"10.1016/j.ecoenv.2024.116668\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhou, X., Sun, L.J.: Study on spectral characteristics of dissolved organic matter (DOM) from biochar [J]. J. Ecol. Rural Environ. \u003cb\u003e39\u003c/b\u003e(06), 819\u0026ndash;826 (2023). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.19741/j.issn.1673-4831.2021.0775\u003c/span\u003e\u003cspan address=\"10.19741/j.issn.1673-4831.2021.0775\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang, Z.Q.C.D.: Difference analysis of material structure evolution time series of dissolved organic matter and humic acid during composting of different materials [J]. J. Environ. Eng. Technol. \u003cb\u003e13\u003c/b\u003e(04), 1514\u0026ndash;1524 (2023). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.12153/j.issn.1674-991X.20221230\u003c/span\u003e\u003cspan address=\"10.12153/j.issn.1674-991X.20221230\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang, Z.M.L.Z., Liao, Y., Zhou, H.Y.Z.: Phage lysate can regulate the humification process of composting. Waste Manage. \u003cb\u003e178\u003c/b\u003e, 221\u0026ndash;230 (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.wasman.2024.02.039\u003c/span\u003e\u003cspan address=\"10.1016/j.wasman.2024.02.039\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"waste-and-biomass-valorization","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"wave","sideBox":"Learn more about [Waste and Biomass Valorization](http://link.springer.com/journal/12649)","snPcode":"12649","submissionUrl":"https://submission.nature.com/new-submission/12649/3","title":"Waste and Biomass Valorization","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Compost, Dissolved organic matter, Sheep manure, Spectral changes, Weathered coal","lastPublishedDoi":"10.21203/rs.3.rs-6995195/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6995195/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe effects of weathered coal on the maturity of sheep manure compost were investigated by studying the spectral changes in dissolved organic matter (DOM) in sheep manure compost. Sheep manure was used as the raw material for compost fermentation, with 10% and 15% weathered coal added. Total organic carbon analysis, ultraviolet-visible absorption spectroscopy, Fourier transform infrared spectroscopy, fluorescence spectroscopy, and three-dimensional excitation emission matrix fluorescence spectroscopy were used to study the spectral changes in DOM in sheep manure compost after the addition of different proportions of weathered coal. Weathered coal had a significant effect on DOM during sheep manure composting. The non-humic organic matter with the same DOM concentration continued to condense to produce humus, increasing the benzene ring structure of the organic matter and enhancing the humification degree of the compost, indicating that the degree of compost maturation increased. Additionally, a portion of humic acid was converted to fulvic acid during composting, and the addition of 15% weathered coal accelerated the composting process. The addition of weathered coal facilitated the synthesis of humic acid in DOM and reduced the soluble salt content in sheep manure. The findings provide a theoretical basis for the collaborative and comprehensive utilization of aquaculture waste and weathered coal resources.\u003c/p\u003e","manuscriptTitle":"Effect of weathered coal on spectral changes of dissolved organic matter during sheep manure composting","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-01 10:14:46","doi":"10.21203/rs.3.rs-6995195/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-08-11T06:19:12+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-27T16:07:20+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Waste and Biomass Valorization","date":"2025-07-19T21:01:15+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-01T11:48:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"Waste and Biomass Valorization","date":"2025-06-27T23:29:24+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"waste-and-biomass-valorization","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"wave","sideBox":"Learn more about [Waste and Biomass Valorization](http://link.springer.com/journal/12649)","snPcode":"12649","submissionUrl":"https://submission.nature.com/new-submission/12649/3","title":"Waste and Biomass Valorization","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"24b7b42e-6d14-4af1-a0e0-c89ff87bb0d0","owner":[],"postedDate":"August 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-22T16:05:32+00:00","versionOfRecord":{"articleIdentity":"rs-6995195","link":"https://doi.org/10.1007/s12649-025-03452-4","journal":{"identity":"waste-and-biomass-valorization","isVorOnly":false,"title":"Waste and Biomass Valorization"},"publishedOn":"2025-12-20 15:57:58","publishedOnDateReadable":"December 20th, 2025"},"versionCreatedAt":"2025-08-01 10:14:46","video":"","vorDoi":"10.1007/s12649-025-03452-4","vorDoiUrl":"https://doi.org/10.1007/s12649-025-03452-4","workflowStages":[]},"version":"v1","identity":"rs-6995195","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6995195","identity":"rs-6995195","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}