Evaluation of the synergistic effects of biochar and biogas residue on CO2 and CH4 emission, functional genes, and enzyme activity during straw composting

Variation of microbial necromass carbon and its potential relationship with humification during composting of chicken manure with and without biochar addition

Microbial necromass carbon (MNC) is an important stable organic C component. However, the variation of MNC and its potential relationship with humus components in composting remains uncertain. During a 45-day chicken manure composting study with and without biochar, MNC ranged from 24.9 to 77.9 g/kg and increased significantly by 80.9 % to 133 %. MNC constituted 5.77 % to 21.3 % of total organic C, with bacterial/fungal necromass C ratio ranging from 0.82 to 1.78. The MNC/humus C ratio ranged from 0.15 to 0.55, and humic acid C showed significant positive associations with bacterial necromass C (R2 = 0.72) and fungal necromass C (R2 = 0.51). Biochar addition reduced electrical conductivity and moisture content, increased pH, and induced microbial phosphorus limitation, thereby enhancing MNC content by 29.2 % and promoting humification. Our study is the first to elucidate the relationship between microbial necromass and humus substances, providing fundamental data for advancing the microbial carbon pump theory in composting.

Effects of exogenous thermophilic bacteria and ripening agent on greenhouse gas emissions, enzyme activity and microbial community during straw composting

This research examined the impact of exogenous thermophilic bacteria and ripening agents on greenhouse gas (GHG) emission, enzyme activity, and microbial community during composting. The use of ripening agents alone resulted in a 30.9 % reduction in CO2 emissions, while the use of ripening agents and thermophilic bacteria resulted in a 50.8 % reduction in N2O emissions. Pearson's analysis showed that organic matter and nitrate nitrogen were the key parameters affecting GHG emissions. There was an inverse correlation between CO2 and CH4 releases and methane monooxygenase α subunit and N2O reductase activity (P<0.05). Additionally, N2O emissions were positively related to β-1, 4-N-acetylglucosaminidase, and ammonia monooxygenase activity (P<0.05). Deinococcota, Chloroflexi, and Bacteroidota are closely related to CO2 and N2O emissions. Overall, adding thermophilic bacteria represents an effective strategy to mitigate GHG emissions during composting.

Selection of Suitable Organic Amendments to Balance Agricultural Economic Benefits and Carbon Sequestration

Long-term excessive use of fertilizers and intensive cultivation not only decreases soil organic carbon (SOC) and productivity, but also increases greenhouse gas emissions, which is detrimental to sustainable agricultural development. The purpose of this paper is to identify organic amendments suitable for winter wheat growth in the North China Plain by studying the effects of organic amendments on the economic benefits, carbon emissions, and carbon sequestration for winter wheat fields and to provide a theoretical basis for the wide application of organic amendments in agricultural fields. The two nitrogen rates were N0 (0 kg ha-1) and N240 (240 kg ha-1), and the four organic amendments were straw, manure, mushroom residue (M R), and biochar. The results showed that, compared to N0, N240 significantly increased the yield by 244.1-318.4% and the organic carbon storage by 16.7-30.5%, respectively, but increased the carbon emissions by 29.3-45.5%. In addition, soil carbon stocks increased with all three types of organic amendments compared to the straw amendment, with the biochar treatment being the largest, increasing carbon storage by 13.3-33.6%. In terms of yield and economic benefits, compared to the straw amendment, the manure and biochar amendments increased winter wheat yields by 0.0-1.5% and 4.0-13.3%, respectively, and M R slightly decreased wheat yield; only the economic benefit of the M R amendment was greater than that of the straw amendment, with an increase in economic benefit of 1.3% and 8.2% in the 2021-2022 and 2022-2023 seasons, respectively. Furthermore, according to the net ecosystem productivity (NEP), N0 was the source of CO2, while N240 was a sink of CO2. The TOPSIS results showed that N240 with a mushroom residue amendment could be recommended for increasing soil carbon stocks and economic benefits for winter wheat in the NCP and similar regions. Low-cost M R can increase farmer motivation and improve soil organic carbon, making a big step forward in the spread of organic materials on farmland.

Effects of agricultural mulch film on swine manure composting: Film degradation and nitrogen transformation

The utilization of biodegradable mulch films (bio-MFs) is essential for agricultural safety. This study explored the effects of no MF (CK), aging bio-MF (BM), non-aging bio-MF (NBM), and aging polyethylene (PE)-MF (PEM) on swine manure composting. The results demonstrated that outdoor aging (45 days) accelerated the macroscopic degradation of bio-MF in the BM. A reduction in NH4+-N and NH3 emissions in the initial composting was observed owing to an increase in the carbon source or the bulking effect provided by the MFs. N2O emissions from days 9 to 21 were higher in the PEM than other treatments because of the formation of anaerobic zone in the MF-based aggregates. An obvious increase of amoA in PEM indicated a promoted nitrification during the maturation phase, meanwhile the increase of NO2--N and aggregate promoted denitrification. Altogether, MF influenced composting through the synergistic effects of increasing the carbon source, bulking effect, and aggregates.

Greenhouse gas emission characteristics and influencing factors of agricultural waste composting process: A review

China, being a major agricultural nation, employs aerobic composting as an efficient approach to handle agricultural solid waste. Nevertheless, the composting process is often accompanied by greenhouse gas emissions, which are known contributors to global warming. Therefore, it is urgent to control the formation and emission of greenhouse gases from composting. This study provides a comprehensive analysis of the mechanisms underlying the production of nitrous oxide, methane, and carbon dioxide during the composting process of agricultural wastes. Additionally, it proposes an overview of the variables that affect greenhouse gas emissions, including the types of agricultural wastes (straw, livestock manure), the specifications for compost (pile size, aeration). The key factors of greenhouse gas emissions during composting process like physicochemical parameters, additives, and specific composting techniques (reuse of mature compost products, ultra-high-temperature composting, and electric-field-assisted composting) are summarized. Finally, it suggests directions and perspectives for future research. This study establishes a theoretical foundation for achieving carbon neutrality and promoting environmentally-friendly composting practices.

Recent Trends and Advances in Additive-Mediated Composting Technology for Agricultural Waste Resources: A Comprehensive Review

Agriculture waste has increased annually due to the global food demand and intensive animal production. Preventing environmental degradation requires fast and effective agricultural waste treatment. Aerobic digestion or composting uses agricultural wastes to create a stabilized and sterilized organic fertilizer and reduces chemical fertilizer input. Indeed, conventional composting technology requires a large surface area, a long fermentation period, significant malodorous emissions, inferior product quality, and little demand for poor end results. Conventional composting loses a lot of organic nitrogen and carbon. Thus, this comprehensive research examined sustainable and adaptable methods for improving agricultural waste composting efficiency. This review summarizes composting processes and examines how compost additives affect organic solid waste composting and product quality. Our findings indicate that additives have an impact on the composting process by influencing variables including temperature, pH, and moisture. Compost additive amendment could dramatically reduce gas emissions and mineral ion mobility. Composting additives can (1) improve the physicochemical composition of the compost mixture, (2) accelerate organic material disintegration and increase microbial activity, (3) reduce greenhouse gas (GHG) and ammonia (NH3) emissions to reduce nitrogen (N) losses, and (4) retain compost nutrients to increase soil nutrient content, maturity, and phytotoxicity. This essay concluded with a brief summary of compost maturity, which is essential before using it as an organic fertilizer. This work will add to agricultural waste composting technology literature. To increase the sustainability of agricultural waste resource utilization, composting strategies must be locally optimized and involve the created amendments in a circular economy.

Bentonite addition enhances the biodegradation of petroleum pollutants and bacterial community succession during the aerobic co-composting of waste heavy oil with agricultural wastes

Soil contamination with petroleum significantly threatens the ecological equilibrium and human health. In this context, aerobic co-composting of waste heavy oil with agricultural wastes was performed in the present study to remediate petroleum pollutants through four treatments: CK (control), T1 (petroleum pollutant), T2 (petroleum pollutant with bentonite), and T3 (petroleum pollutant with humic acid-modified bentonite). Comprehensive analyses were conducted to determine the physicochemical parameters, enzymatic activities, removal of petroleum pollutants, microbial community structure, and water-extractable organic matter in different composting systems. Structural equation modeling was employed to identify the key factors influencing the removal of petroleum pollutants. According to the results, petroleum pollutant removal percentages of 44.94%, 79.09%, and 79.67% could be achieved with T1, T2, and T3, respectively. In addition, the activities of polyphenol oxidase (51.21 U/g) and catalase (367.91 U/g), which are the enzymes related to petroleum hydrocarbon degradation, were the highest in T3. Moreover, bentonite addition to the treatment increased the nitrate nitrogen storage in the compost from 10.95 mg/kg in T1 to 18.63 and 17.41 mg/kg in T2 and T3, respectively. Humic acid-modified bentonite could enhance the degree of compost humification, thereby leading to a higher-quality compost product. Collectively, these findings established bentonite addition as an efficient approach to enhance the compost remediation of petroleum pollutants.

Relative contribution of ammonia-oxidizing bacteria and denitrifying fungi to N2O production during rice straw composting with biochar and biogas residue amendments

Nitrous oxide (N2O) production is associated with ammonia-oxidizing bacteria (amoA-AOB) and denitrifying fungi (nirK-fungi) during the incorporation of biochar and biogas residue composting. This research examined the relative contribution of alterations in the abundance, diversity and structure of amoA-AOB and nirK-fungi communities on N2O emission by real-time PCR and sequence processing. Results showed that N2O emissions showed an extreme relation with the abundance of amoA-AOB (rs = 0.584) while giving credit to nirK-fungi (rs = 0.500). Nitrosomonas and Nitrosospira emerged as the dominant genera driving ammoxidation process. Biogas residue changed the community structure of AOB by altering Nitrosomonadaceae proportion and physiological capacity. The denitrification process, primarily governed by nirK-fungi, served as a crucial pathway for N2O production, unveiling the pivotal mechanism of biochar to suppress N2O emissions. C/N and NH4+-N were identified as significant parameters influencing the distribution of nirK-fungi, especially Micromonospora, Halomonas and Mesorhizobium.

Synergistic effects of biochar derived from different sources on greenhouse gas emissions and microplastics mitigation during sewage sludge composting

This study aimed to investigate the effects of biochar derived from different sources (wheat straw, sawdust and pig manure) on greenhouse gas and microplastics (MPs) mitigation during sewage sludge composting. Compared to the control, all biochar significantly reduced the N2O by 28.91-41.23%, while having no apparent effect on CH4. Sawdust biochar and pig manure biochar significantly reduced the NH3 by 12.53-23.53%. Adding biochar decreased the global warming potential during composting, especially pig manure biochar (177.48 g/kg CO2-eq.). The concentration of MPs significantly increased in the control (43736.86 particles/kg) compared to the initial mixtures, while the addition of biochar promoted the oxidation and degradation of MPs (15896.06-23225.11 particles/kg), with sawdust biochar and manure biochar were more effective. Additionally, biochar significantly reduced the abundance of small-sized (10-100 μm) MPs compared to the control. Moreover, biochar might regulate specific microbes (e.g., Thermobifida, Bacillus and Ureibacillus) to mitigate greenhouse gas emissions and MPs degradation.

Co-application of biochar and organic amendments on soil greenhouse gas emissions: A meta-analysis

Biochar has been shown to reduce soil greenhouse gas (GHG) and increase nutrient retention in soil; however, the interaction between biochar and organic amendments on GHG emissions remain largely unclear. In this study, we collected 162 two-factor observations to explore how biochar and organic amendments jointly affect soil GHG emissions. Our results showed that biochar addition significantly increased soil CO2 emission by 8.62 %, but reduced CH4 and N2O emissions by 27.0 % and 23.9 %, respectively. Meanwhile, organic amendments and the co-application with biochar resulted in an increase of global warming potential based on the 100-year time horizon (GWP100) by an average of 18.3 % and 26.1 %. More importantly, the interactive effect of biochar and organic amendments on CO2 emission was antagonistic (the combined effect was weaker than the sum of their individual effects), while additive on CH4 and N2O emissions. Additionally, our results suggested that when biochar is co-applied with organic amendments, soil GHG emissions were largely influenced by soil initial total carbon, soil texture, and biochar feedstocks. Our work highlights the important interactive effects of biochar and organic amendments on soil GHG emissions, and provides new insights for promoting ecosystem sustainability as well as mitigating future climate change.

Identifying the specific pathways to improve nitrogen fixation of different straw biochar during chicken manure composting based on its impact on the microbial community

The application of straw biochar to chicken manure composting mitigated nitrogen loss. However, the impact of biochar derived from different types of straw on nitrogen fixation in chicken manure composting is discrepant, and the specific pathways remain unclear. Therefore, this study aimed to clarify the specific pathways of maize straw biochar (M) and rice straw biochar (R) to improve nitrogen fixation during chicken manure composting. The nitrogen losses in control (no addition, CK), M, and R composting were 51.84 %, 33.47 %, and 38.24 %, respectively, suggesting that adding straw biochar effectively improved nitrogen fixation. Microbial community analysis suggested that inhibiting denitrification and NH4+-N transformation by microorganisms was the primary means of improving nitrogen fixation. Meanwhile, biochar addition reduced the number of bacteria participating in nitrogen transformation and strengthened the NO3--N and total organic nitrogen transformation processes, among which the effect of M composting was stronger. The stronger effect was attributed to the significant role of the core microorganisms in M composting in shifting the transformation processes of the nitrogen components (P < 0.05). Therefore, the function of different straw biochar was determined by its different impacts on the microbial community, highlighting the important role of microbial community variability.

Nutrient-cycling functional gene diversity mirrors phosphorus transformation during chicken manure composting

Elucidating ecological mechanism underlying phosphorus transformation mediated by phosphate-solubilizing bacteria (PSB) during manure composting is an important but rarely investigated subject. The research objective is to disentangle ecological functions of the inoculation of PSB Pseudomonas sp. WWJ-22 during chicken manure composting based on gene quantification and amplicon sequencing. There are large dynamic changes in phosphorus fractions, gene abundances, and bacterial community structure. The PSB addition notably increased available phosphorus from 0.29-0.89 g kg-1 to 0.49-1.39 g kg-1 and significantly affected phosphorus fractionation. The PSB inoculation significantly affected composition of nutrient-cycling functional genes (NCFGs), and notably influenced bacterial community composition and function. Compost bacteria showed significant phylogenetic signals in response to phosphorus fractions, and stochastic processes dominated bacterial community assembly. Results emphasized that PSB addition increased functional redundancy, phylogenetic conservatism, and stochasticity-dominated assembly of bacterial community. Overall, findings highlight NCFG diversity can be a bio-indicator to mirror phosphorus transformation.

Utilization of agricultural residues for energy and resource recovery towards a sustainable environment

Fungal pre-treatment using Pleurotus ostreatus (PO) was carried out on individual and combinations of agro-waste wheat straw (WS), rice straw (RS), and pearl millet straw (PMS) with the addition of biochar (5%,7.5% and 10%) to reduce the pre-treatment duration. Further remaining substrate known as spent mushroom substrate (SMS) was used in anaerobic digestor (AD) for estimation enhanced biomethane yield. Equal ratios of RS + WS, WS + PMS, PMS + RS, and RS + PMS + WS and biochar addition were taken for enhancing pre-treatment, PO growth and AD process. The extent of pre-treatment was recorded with the maximum lignin removal of 40.4% for RS + PMS + WS as compared to untreated counterparts and 0.5%, 2.2%, and 3.3% times more lignin removal from individual PMS, RS, and WS respectively. Addition of biochar to the substrates reduced the total pre-treatment duration by days as compared to the non-biochar substrates. Biological efficiency (BE) used for the analysis of mushroom growth varied from 51-92%. Further, the average bio-methane yield was 187 ml/gVS for SMS of PMS + WS + RS with 10% biochar indicating an increment of 83.33% from untreated SMS of PMS + WS + RS. This, higher biomethane yield was 9.35%, 22.22% and 57.14% times higher than individual SMS of PMS, RS, and WS respectively. The current study shows that biochar not only enhances the bio-methane yield but also reduces the biological pre-treatment duration and removes the dependency on one lignocellulosic biomass for energy (bio-methane) and food (mushroom) production.

Enhancement of nitrogen removal in coupling Anammox and DAMO via Fe-modified granular activated carbon

Anaerobic ammonium oxidation (Anammox) coupled with Denitrifying anaerobic methane oxidation (DAMO) is an attractive technology to simultaneously remove nitrogen and mitigate methane emissions from wastewater. However, its nitrogen removal rate is usually limited due to the low methane mass transfer efficiency, low metabolic activity and slow growth rate of functional microorganisms. In this study, GAC and Fe-modified GAC (Fe-GAC) were added into Anammox-DAMO process to investigate their effects on nitrogen removal rates and then reveal the mechanism. The results showed that after 80-day experiments, the total nitrogen removal rate was slightly improved in the presence of GAC (3.94 mg L^-1·d^-1), while it reached high as 16.66 mg L^-1·d^-1 in the presence of Fe-GAC, which was ca.17 times that of non-amended control group (0.96 mg L^-1·d^-1). The addition of Fe-GAC stimulated the secretion of extracellular polymeric substance (EPS), improved the electron transfer capability and promoted the production of Cytochrome C. Besides, the key functional enzyme activities (HZS, HDH and NAR) were highest in the Fe-GAC group, which were approximately 1.06-1.56 times higher than those of GAC-amended and blank control groups. Microbial community analysis showed that the abundance of the DAMO archaea (Candidatus Methanoperedens) and Anammox bacteria (Candidatus Brocadia) were remarkably increased with the addition of Fe-GAC. Functional genes associated with nitrogen removal and methane oxidation in Fe-GAC system were up-regulated. This study provides a promising strategy for achieving high rate of nitrogen removal upon Anammox-DAMO process.

Impacts of adding FeSO4 and biochar on nitrogen loss, bacterial community and related functional genes during cattle manure composting

This study investigated the impacts of adding FeSO₄ and biochar to cattle manure and rice straw composts on functional genes controlling nitrogen loss, bacterial community, nitrification, and denitrification. Four treatments were established, including a control group (CP), and CP mixtures that included 4% biochar (TG1), 4% FeSO₄ (TG2), or 2% FeSO₄ and 2% biochar (TG3). Compared to CP, TG1-3 had a lower total nitrogen loss rate, and TG3 resulted in reduced NH₃ (52.4%) and N₂O (35.6%) emissions to mitigate nitrogen loss. The abundance of amoA and narG gene in TG3 was higher than in the other groups, and TG3 was beneficial to the growth of Proteobacteria and Actinobacteria. According to redundancy and Pearson analysis, TG3 had a positive effect on the nitrification process by increasing the abundance of amoA and narG. Thus, biochar and FeSO₄ addition mitigate nitrogen loss by regulating the nitrification processes.

Biochar preparation and evaluation of its effect in composting mechanism: A review

This article provides an overview of biochar application for organic waste co-composting and its biochemical transformation mechanism. As a composting amendment, biochar work in the adsorption of nutrients, the retention of oxygen and water, and the promotion of electron transfer. These functions serve the micro-organisms (physical support of niche) and determine changes in community structure beyond the succession of composing primary microorganisms. Biochar mediates resistance genes, mobile gene elements, and biochemical metabolic activities of organic matter degrading. The participation of biochar enriched the α-diversity of microbial communities at all stages of composting, and ultimately reflects the high γ-diversity. Finally, easy and convincing biochar preparation methods and characteristic need to be explored, in turn, the mechanism of biochar on composting microbes at the microscopic level can be studied in depth.

Treatment of amoxicillin-containing wastewater by Trichoderma strains selected from activated sludge

This study screened a Trichoderma strain (Trichoderma pubescens DAOM 166162) from activated sludge to solve the limitation of traditional biological processes in the treatment of amoxicillin (AMO) containing wastewater. The mechanism of the removal of AMO wastewater by T. pubescens DAOM 166162 (TPC) was studied. AMO resulted in a higher protein percentage in the extracellular polymeric substances (EPS) secreted by TPC, which facilitated the removal of AMO from the wastewater. Fourier transform infrared spectroscopy and excitation-emission matrix were used to characterize EPS produced by metabolizing different carbon sources. It was found that the hydroxyl group was the primary functional group in EPS. The life activity of TPC was the cause of the pH rise. The main pathway of degradation of AMO by TPC was the hydroxyl group uncoupling the lactam ring and the hydrolysis of AMO in an alkaline environment. The removal efficiency of AMO in wastewater by TPC was >98 % (24 h), of which the biodegradation efficiency was 70.01 ± 1.48 %, and the biosorption efficiency was 28.44 ± 2.97 %. In general, TPC is an effective strain for treating wastewater containing AMO. This research provides a new idea for AMO wastewater treatment.

A review of additives use in straw composting

Straw composting is not only a process of decomposition and re-synthesis of organic matter, but also a process of harmless treatment, avoiding air pollution caused by straw burning. Many factors, including raw materials, humidity, C/N, and microbial structure, may determine the composting process and the quality of final product. In recent years, many researches have focused on composting quality improvement by adding one or more exogenous substances, including inorganic additives, organic additives, and microbial agents. Although a few review publications have compiled the research on the use of additives in composting, none of them has specifically addressed the composting of crop straw. Additives used in straw composting can increase degradation of recalcitrant substances and provide ideal living surroundings for microorganism, and thus reduce nitrogen loss and promote humus formation, etc. This review's objective is to critically evaluate the impact of various additives on straw composting process, and analyze how these additives enhance final quality of composting. Furthermore, a vision for future perspectives is provided. This paper can serve as a reference for straw composting process optimization and composting end-product improvement.

Insights into carbon loss reduction during aerobic composting of organic solid waste: A meta-analysis and comprehensive literature review

Carbon neutrality is now receiving global concerns for the sustainable development of human societies, of which how to reduce greenhouse gases (GHGs) emissions and enhance carbon conservation and sequestration becomes increasingly critical. Therefore, this study conducted a meta-analysis and literature review to assess carbon loss and to explore the main factors that impact carbon loss during organic solid waste (OSW) composting. The results indicated that over 40 % of carbon was lost through composting, mainly as CO₂-C and merely as CH₄-C. Experimental scale, feedstock varieties, composting systems, etc., all impacted the carbon loss, and there was generally higher carbon loss under optimal conditions (i.e., C/N ratio (15-25), pH (6.5-7.5), moisture content (65-75 %)). Most mitigation strategies in conventional composting (CC) systems (e.g., additive supplementary, feedstock adjustment, and optimized aeration, etc.) barely mediated the TC and CO₂-C loss but dramatically reduced the emission of CH₄-C through composting. Among them, feedstock adjustment by elevating the feedstock C/N ratio effectively reduced the TC loss, and chemical additives facilitated the conservation of both carbon and nitrogen. By comparison, there was generally higher carbon loss in the novel composting systems (e.g. hyperthermophilic and electric field enhanced composting, etc.). However, the impacts of different mitigation strategies and novel composting systems on carbon loss reduction through composting were probably underestimated for the inappropriate evaluation methods (composting period-dependent instead of maturity originated). Therefore, further studies are needed to explore carbon transformation through composting, to establish methods and standards for carbon loss evaluation, and to develop novel techniques and systems for enhanced carbon conservation through composting. Overall, the results of this study could provide a reference for carbon-friendly composting for future OSW management under the background of global carbon neutrality.

Response characteristics of antibiotic resistance genes and bacterial communities during agricultural waste composting: Focusing on biogas residue combined with biochar amendments

This research investigated biogas residue and biochar addition on antibiotic resistance genes (ARGs), mobile genetic elements (MGEs), and changes in bacterial community during agricultural waste composting. Sequencing technique investigated bacterial community structure and ARGs, MGEs changes. Correlations among physicochemical factors, ARGs, MGEs, and bacterial community structure were determined using redundancy analysis. Results confirmed that biochar and biogas residue amendments effectively lowered the contents of ARGs and MGEs. The main ARGs detected was sul1. Proteobacteria and Firmicutes were the main host bacteria strongly associated with the dissemination of ARGs. The dynamic characteristics of the bacterial community were strongly correlated with pile temperature and pH (P < 0.05). Redundancy and network analysis revealed that nitrate, intI1, and Firmicutes mainly affected the in ARGs changes. Therefore, regulating these key variables would effectively suppress the ARGs spread and risk of compost use.

Community succession of microbial populations related to CNPS biological transformations regulates product maturity during cow-manure-driven composting

The main objective of present study was to understand the community succession of microbial populations related to carbon-nitrogen-phosphorus-sulfur (CNPS) biogeochemical cycles during cow-manure-driven composting and their correlation with product maturity. The abundance of microbial populations associated with C degradation, nitrification, cellular-P transport, inorganic-P dissolution, and organic-P mineralization decreased gradually with composting but increased at the maturation phase. The abundance of populations related to N-fixation, nitrate-reduction, and ammonification increased during the mesophilic stage and decreased during the thermophilic and maturation stages. The abundance of populations related to C fixation and denitrification increased with composting; however, the latter tended to decrease at the maturation stage. Populations related to organic-P mineralization were the key manipulators regulating compost maturity, followed by those related to denitrification and nitrification; those populations were mediated by inorganic N and available P content. This study highlighted the consequence of microbe-driven P mineralization in improving composting efficiency and product quality.

Dissolved organic matter evolution can reflect the maturity of compost: Insight into common composting technology and material composition

Dissolved organic matter (DOM) can clearly reflect composting components changes, thus it is supposed to indicate the humification process during composting. To demonstrate this, three compost mixtures and two techniques were arranged. DOM evolution was detected by three spectral techniques. X-ray diffraction (XRD) showed that the crystal structure substances decreased gradually during the composting, including cellulose, struvite, sylvine, quartz, and calcite; Specifically, the struvite was found, which was conducive to the fixation of nitrogen and phosphorus. Fourier transform infrared spectroscopy (FTIR) and three-dimensional fluorescence spectroscopy (3D-EEM) further showed that pig manure-based mixtures, added cabbage, and windrow composting are beneficial to sugar, protein, fulvic acid, and soluble microbial by-products decompose and humic acids produce. This process was closely related to the change of physical-chemical parameters (temperature; pH; moisture content; and NH₄⁺-N content) and maturity index (C/N ratio, E₄/E₆ and GI). Therefore, DOM evolution could quickly reflect the maturity process of compost. In subsequent research, the quantitative analysis of DOM components can be considered to modify DOM spectral parameters, or to build a model, so as to achieve rapid evaluation of compost maturity.

Characteristics of carbon, nitrogen, phosphorus and sulfur cycling genes, microbial community metabolism and key influencing factors during composting process supplemented with biochar and biogas residue

Carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) cycling functional genes and bacterial and fungal communities during composting with biochar and biogas residue amendments were studied. Correlations between microbial community structure, functional genes and physicochemical properties were investigated by network analysis and redundancy analysis. It was shown that the gene of acsA abundance accounted for about 50% of the C-related genes. Biogas residue significantly decreased the abundance of denitrification gene nirK. Biogas residues can better promote the diversity of bacteria and fungi during composting. Biochar significantly increased the abundance of Humicola. Redundancy analysis indicated that pile temperature, pH, EC were the main physicochemical factors affecting the microbial community. WSC and NO₃^--N have significant correlation with C, N, P, S functional genes. The research provides a theoretical basis for clarifying the metabolic characteristics of microbial communities during composting and for the application of biochar and biogas residues in composting.