Effects of carbon/nitrogen ratio and aeration rate on the sheep manure composting process and associated gaseous emissions

Enhancing compost quality: Biochar and zeolite's role in nitrogen transformation and retention

This research evaluated how addition of biochar and zeolite affected nitrogen transformation and retention during the composting of kitchen waste. Four treatments, control (CK), 10 % biochar (B), 10 % zeolite (Z), and 5 % biochar +5 % zeolite (BZ) were used to study nitrogen transformation and retention. The results showed that biochar and zeolite can significantly reduce the loss of NH4+-N during the thermophilic phase (CK: 42.6 %, B: 35.1 %, Z: 35.7 %, and BZ: 31.3 %). Network analysis showed that biochar and zeolite increased the number of microorganisms associated with nitrification genes while decreasing the number of microorganisms associated with denitrification genes, preventing nitrogen volatilization in N2O. Mantel tests further demonstrated that biochar and zeolite enhanced the correlation between bacterial communities and the relationship between NH4+-N, NO3--N, and organic nitrogen was weakened, thus inhibiting the mineralization of organic nitrogen. Therefore, biochar and zeolite played an active role in promoting the transformation and retention of nitrogen components. Biochar and zeolite for kitchen waste also provided a new perspective on the treatment of kitchen waste.

Bioaugmentation strategies in co-composting anaerobically digested food waste with agricultural by-products: Enhancing fertilizer quality and microbial communities

Effective management of urban solid waste is critical for achieving sustainable development goals. One key aspect of this challenge is the recycling of anaerobically digested residues from anaerobic digestion of food waste, which plays a pivotal role in promoting sustainability. However, there is a gap in understanding the feasibility and effectiveness of converting these digested residues into valuable fertilizers through composting. Addressing this gap, the present study explored the potential of composting anaerobically digested residue and evaluated the quality of the co-compost products. In this study, we investigated the composting process using a mixture of rice straw, food waste, sheep manure and mature composted residues (RFM group) alongside the anaerobically digested residues. The results demonstrated that the composting process quickly reached the thermophilic stage, during which NH+4-N concentrations increased and C/N ratio decrease. The RFM group exhibited the highest humic acid content compared to other groups. Additionally, microbial analysis revealed key species such as Clostridium, Moheibacter, Bacillus, Thermobacillus, and Pseudogracilibacillus as major contributors to the composting process. The germination index (GI) test indicated that the co-composted residues were non-toxic to plants, suggesting their suitability as a fertilizer. All these works indicated that the addition of rice straw, food waste, and mature composted residues to anaerobically digested materials significantly enhanced the composting process, resulting in a high-quality co-compost. This approach not only provided a promising method for recycling food waste but also contributed to the broader goal of sustainable solid waste management.

The biological mechanism of a lower carbon/nitrogen ratio increases methane emissions during vegetable waste composting

The initial carbon/nitrogen (C/N) ratio is one of the most important factors impacting composting processes, such as methane (CH4) emissions. However, the effects of the C/N ratio on CH4 emissions and the associated biological mechanisms during vegetable waste composting are largely unknown. In this study, a lab-scale experiment was conducted to investigate the effects of different C/N ratios on CH4 emissions and the mechanisms associated with methane-metabolizing microorganisms (methanogens and methanotrophs) during capsicum straw composting. The initial C/N ratios were set to 18, 30 and 50 to simulate the low (L), medium (M) and high (H) C/N ratios, respectively. The results showed that CH4 emissions were mainly concentrated in the thermophilic phase and that the cumulative CH4 emissions were significantly greater in the L treatment than in the M and H treatments by 10.8 and 15.4 times, respectively. During the methanogenic process, the relative abundance of the dominant genus Methanoculleus (47.59 % ∼ 76.92 %) was higher than in the L treatment than in the M and H treatments at the thermophilic and maturation stages, and the Chao1 index and the mcrA gene abundance followed the order of L > M > H at each composting stage. During the methanotrophic process, the dominant genus unclassified_d_bacteria (51.3 % ∼ 91.87 %), Chao1 index, pmoA gene abundance and CO2 emissions were in the order of L > M > H at each composting stage. This pattern suggests that a lower C/N ratio simultaneously enhanced CH4 production and oxidation. A structural equation model further revealed that the methanogenic community, which was driven directly by the relative contents of hemicellulose and cellulose in the substrates, as indicated by the C/N ratio, made greater contributions to CH4 emissions than did the methanotrophic community. In conclusion, a lower C/N ratio increased CH4 emissions mainly by regulating the population and composition of methanogen community.

Insights from meta-analysis on carbon to nitrogen ratios in aerobic composting of agricultural residues

Given the heterogeneity of raw materials, the diversity of composting processes, and the complexity of biological transformations, systematically exploring the critical role of the initial carbon-to-nitrogen (C/N) ratio in the aerobic composting of agricultural residues is challenging within a single experimental study. This study employs meta-analysis to investigate this role. Statistical analysis of 192 scholarly articles confirmed that most studies adhere to the recommended optimal initial C/N range of 25 and 30, where enhanced compost maturity and nutrient accumulation are observed. The findings indicate that optimal initial C/N ratios vary by agricultural residue type. A C/N ratio of 20 to 30 facilitates controlling the composting duration within 45 days, while a C/N ratio of 30 to 35 necessitates extending the duration beyond 45 days. The study highlights the effectiveness of adjusting the C/N ratio and applying microbial inoculants and physical amendments to optimize composting outcomes and control the composting duration.

Predicting ammonia emissions and global warming potential in composting by machine learning

The amounts of gases emitted from composting are key to evaluating global warming potential (GWP). However, few methods can accurately predict the quantities of relevant gas emissions. In this study, three developed machine-learning models were used to predict NH3 emissions and GWP. The extreme gradient boosting model provided the best predictions (R2 > 90 %) compared to random forest, making it a suitable method for calculating NH3 emissions and GWP. The k-nearest neighbor classification model was utilized to determined compost maturity achieving 92 % accuracy. Shapley Additive ExPlanation analysis was applied to identify key factors influencing gas emissions and maturity. Aeration rate, carbon-to-nitrogen ratio and moisture content showed high importance in decreasing order for predicting NH3 emissions, while NO3- was the most significant factor for predicting GWP. Practical applications of predictive models suggested that prediction of GWP was 792614 Mg CO2e year-1 close to annual calculation of 789000 Mg CO2e year-1 in California.

Microbe-aided thermophilic composting accelerates manure fermentation

Aerobic composting is a key strategy to the sustainable use of livestock manure, which is however constrained by the slow kinetics. Microbe-aided thermophilic composting provides an attractive solution to this problem. In this study, we identified key thermophilic bacteria capable of accelerating manure composting based on the deciphering of manure bacterial community evolution in a thermophilic system. High-throughput sequencing showed a significant evolution of manure bacterial community structure with the increasing heating temperature. Firmicutes were substantially enriched by the heating, particularly some known thermotolerant bacterial species, such as Novibacillus thermophiles, Bacillus thermolactis, and Ammoniibacillus agariperforans. Correspondingly, through function prediction, we found bacterial taxa with cellulolytic and xylanolytic activities were significantly higher in the thermophilic process relative to the initial stage. Subsequently, a total of 47 bacteria were isolated in situ and their phylogenetic affiliation and degradation capacity were determined. Three isolates were back inoculated to the manure, resulting in shortened composting process from 5 to 3 days with Germination Index increased up to 134%, and improved compost quality particularly in wheat growth promoting. Comparing to the mesophilic and thermophilic Bacillus, the genomes of the three isolates manifested some features similar to the thermophiles, including smaller genome size and mutation of specific genes that enhance heat tolerance. This study provide robust evidence that microbe-aided thermophilic composting is capable to accelerate manure composting and improve the quality of compost, which represents a new hope to the sustainable use of manure from the meat industry.

Optimizing biochar addition strategies in combined processes: Comprehensive assessment of earthworm growth, lignocellulose degradation and vermicompost quality

The sustainable management of agricultural waste is essential for curtailing environmental contamination. To address the shortcomings of single treatment methods, this study evaluated the feasibility of combining membrane-covered composting (MC) with vermicomposting. Based on this, the integrated effects of different biochar addition strategies on the combined process were investigated. The aim was to improve the efficiency of vermicomposting while eliminating the negative effects of biochar on earthworms. Addition of biochar before membrane-covered composting increased total earthworm biomass by 25.6 - 31.4 % and reproduction rate by 13.4 - 23.9 %. Specifically, the electrical conductivity (EC) (1061.0 - 1112.0 uS/cm) of the vermicompost was significantly reduced, while the total nutrient content (42.3 - 42.6 mg/g) and germination index (GI) (103.9 - 108.4 %) were maximized. Additionally, reductions in the carbon-to-nitrogen ratio and volatile content were observed. Overall, combination process is a promising approach to improve the quality of vermicomposting. The study's results offer a novel perspective on the value-added treatment of agricultural waste.

Insight into N2O emission and denitrifier communities under different aeration intensities in composting of cattle manure from perspective of multi-factor interaction analysis

Nitrous oxide (N2O) emission from composting is a significant contributor to greenhouse effect and ozone depletion, which poses a threat to environment. To address the challenge of mitigating N2O emission during composting, this study investigated the response of N2O emission and denitrifier communities (detected by metagenome sequencing) to aeration intensities of 6 L/min (C6), 12 L/min (C12), and 18 L/min (C18) in cattle manure composting using multi-factor interaction analysis. Results showed that N2O emission occurred mainly at mesophilic phase. Cumulative N2O emission (QN2O, 9.79 mg·kg-1 DW) and total nitrogen loss (TN loss, 16.40 %) in C12 composting treatment were significantly lower than those in the other two treatments. The lower activity of denitrifying enzymes and the more complex and balanced network of denitrifiers and environmental factors might be responsible for the lower N2O emission. Denitrification was confirmed to be the major pathway for N2O production. Moisture content (MC) and Luteimonas were the key factors affecting N2O emission, and nosZ-carrying denitrifier played a significant role in reducing N2O emission. Although relative abundance of nirS was lower than that of nirK significantly (P < 0.05), nirS was the key gene influencing N2O emission. Community composition of denitrifier varied significantly with different aeration treatments (R2 = 0.931, P = 0.001), and Achromobacter was unique to C12 at mesophilic phase. Physicochemical factors had higher effect on QN2O, whereas denitrifying genes, enzymes and NOX- had lower effect on QN2O in C12. The complex relationship between N2O emission and the related factors could be explained by multi-factor interaction analysis more comprehensively. This study provided a novel understanding of mechanism of N2O emission regulated by aeration intensity in composting.

Greenhouse gas emission characteristics during kitchen waste composting with biochar and zeolite addition

Aerobic kitchen waste composting can contribute to greenhouse gas (GHGs) emissions and global warming. This study investigated the effects of biochar and zeolite on GHGs emissions during composting. The findings demonstrated that biochar could reduce N2O and CH4 cumulative releases by 47.7 %and 47.9 %, respectively, and zeolite could reduce the cumulative release of CO2 by 28.4 %. Meanwhile, the biochar and zeolite addition could reduce the abundance of potential core microorganisms associated with GHGs emissions. In addition, biochar and zeolite reduced N2O emissions by regulating the abundance of nitrogen conversion functional genes. Biochar and zeolite were shown to reduce the impact of bacterial communities on GHGs emissions. In summary, this study revealed that biochar and zeolite can effectively reduce GHG emissions during composting by altering the compost microenvironment and regulating microbial community structure. Such findings are valuable for facilitating high-quality resource recovery of organic solid waste.

Effects of turning aeration and the initial carbon/nitrogen ratio on the biodegradation of polylactic acid under controlled conditions

Plastic pollution is primarily caused by the accumulation of petroleum-derived plastics, as they tend to degrade slowly. Sustainable alternatives to these materials are bio-based and biodegradable plastics, such as polylactic acid (PLA). In this study, we assessed how turning aeration and the initial carbon/nitrogen (C/N) ratio impact PLA biodegradation. The study was carried out under controlled composting conditions, over 180 days, with the aim of decreasing the biodegradation time of the PLA. Apple pomace, rice husk, grape pomace compost, and PLA were used as substrates in the composting process. The experiments were conducted using three types of turning aeration: without turning, one turn per week, and two turns per week. Three initial C/N ratios were used: 20, 30, and 40. A stepwise temperature ramp was designed and implemented to simulate industrial composting conditions, which influence microbial activity and thus the rate of decomposition of substrates, including PLA. The data showed behavior; hence, a nonlinear regression model based on the logistic growth equation was used to predict the PLA biodegradation at the end of the composting process. The results showed that two turns per week with an initial C/N ratio of 30 or 40 led to a 90 % biodegradation of the PLA in 130 days. This degradation was verified by Fourier-Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM).

Multi-stage aeration regime to regulate organic conversion toward gas alleviation and humification in food waste digestate composting

Aerobic composting has been considered as a pragmatic technique to convert food waste digestate into high-quality biofertiliser. Nevertheless, massive gaseous emission and immature product remain the primary challenges in food waste digestate composting. Thus, the performance of multi-stage aeration regimes to improve gaseous emissions and organic humification during food waste digestate composting was investigated in this study. In addition to continuous aeration with a constant intensity of 0.3 L kg·dry mass (DM)-1·min-1, two multi-stage decreased aeration regimes were designed as "0.3-0.2-0.1" and "0.3-0.1-0.1" L·kg·DM-1·min-1 from the thermophilic to cooling and then mature stages, respectively. Results showed that the decreased aeration regimes could alleviate nitrous oxide (N2O) and ammonia (NH3) emission and slightly enhance humification during composting. The alleviated N2O and NH3 emission were mainly contributed by abiotically reducing gaseous release potential as well as biotically inactivating denitrifers (Pusillimonas and Pseudidiomarina) and proliferating Atopobium to reduce nitrate availability under lower aeration supply. The "0.3-0.2-0.1 L kg·DM-1·min-1" regime exhibited a more excellent performance to alleviate N2O and NH3 emission by 27.5% and 16.3%, respectively. Moreover, the decreased aeration regimes also favored the enrichment of functional bacteria (Caldicoprobacter and Syntrophomonas) to accelerate lignocellulosic biodegradation and thus humic acid synthesis by 6.5%-11.2%. Given its better performance to improve gaseous emissions and humification, the aeration regime of "0.3-0.2-0.1 L kg·DM-1·min-1" are recommended in food waste digestate composting in practice.

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.

Contribution of sulfur-containing precursors to release of hydrogen sulfide in sludge composting

Hydrogen sulfide (H2S) production during composting can impact the environment and human health. Especially during the thermophilic phase, H2S is discharged in large quantities. However, in sludge composting, the contributions of different sulfur-containing precursors to H2S fluxes, key functional microorganisms, and key environmental parameters for reducing H2S flux remain unclear. Analysis of cysteine (Cys), methionine (Met), and sulfate (SO42-) concentrations, multiple stepwise regression analysis, and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation analysis of metagenomes showed that Cys was the main contributor to the production of H2S and that Met was among the main sources during the first three days of composting, while the SO42- contribution to H2S was negligible. Fifteen functional genera involved in the conversion of precursors to H2S were identified by co-occurrence network analysis. Only Bacillus showed high temperature resistance (>50 °C) and the ability to reduce H2S. Redundancy analysis showed that total carbon (64.0 %) and pH (23.3 %) had significant effects on functional bacteria. H2S had a quadratic relationship with sulfur-containing precursors. All microbial network sulfur-containing precursors metabolism modules showed a highly significant relationship with Cys.

Evaluation of compost quality and the environmental effects of semipermeable membrane composting with poultry manure using sawdust or mushroom residue as the bulking agent

Herein, the effects of different bulking agents (sawdust and mushroom residue), on compost quality and the environmental benefits of semipermeable film composting with poultry manure were investigated. The results show that composting with sawdust as the bulking agent resulted in greater efficiency and more cost benefits than composting with mushroom residue, and the cost of sawdust for treating an equal volume of manure was only 1/6 of that of mushroom residue. Additionally, lignin degradation and potential carbon emission reduction in the sawdust group were better than those in the mushroom residue group, and the lignin degradation efficiency of the bottom sample in the sawdust group was 48.57 %. Coupling between lignin degradation and potential carbon emission reduction was also closer in sawdust piles than in mushroom residue piles, and sawdust is more environmentally friendly. The abundance of key functional genes was higher at the bottom of each pile relative to the top and middle. Limnochordaceae, Lactobacillus and Enterococcus were the core microorganisms involved in coupling between lignin degradation and potential carbon emission reduction, and the coupled relationship was influenced by electric conductivity, ammonia nitrogen and total nitrogen in the compost piles. This study provides important data for supporting bulking agent selection in semipermeable film composting and for improving the composting process. The results have high value for compost production and process application.

Magnetic biochar accelerates microbial succession and enhances assimilatory nitrate reduction during pig manure composting

Biochar promotes microbial metabolic activities and reduces N2O on aerobic composting. However, the effects of magnetic biochar (MBC) on the microbial succession and N2O emissions during pig manure composting remain unclear. Herein, a 42-day composting experiment was conducted with five treatment regimes: pig manure without biochar (CK), 5 % pig manure-based biochar (5 % PBC), 2 % MBC (2 % MBC), 5 % MBC (5 % MBC) and 7.5 % MBC (7.5 % MBC)), to clarify the variation in functional microorganisms and genes associated with nitrogen and direct interspecies electron transfer via metagenomics. Fourier-transform infrared spectroscopy showed that MBC possessed more stable aromatic structures than pig manure-based biochar (PBC), indicating its greater potential for nitrous oxide reduction. MBC treatments were more effective in composting organic matter and improving the carbon/nitrogen ratio than PBC. The microbial composition during composting varied significantly, with the dominant phyla shifting from Firmicutes to Proteobacteria, Actinobacteria, and Bacteroidota. Network and hierarchical clustering analyses showed that the MBC treatment enhanced the interactions of dominant microbes (Proteobacteria and Bacteroidota) and accelerated the composting process. The biochar addition accelerated assimilatory nitrate reduction and slowed dissimilatory nitrate reduction and denitrification. The Mantel test demonstrated that magnetic biochar potentially helped regulate composting nutrients and affected functional nitrogen genes. These findings shed light on the role of MBC in mitigating greenhouse gas emissions during aerobic composting.

Relating bacterial dynamics and functions to greenhouse gas and odor emissions during facultative heap composting of four kinds of livestock manure

Although facultative heap composting is widely used in small and medium-sized livestock farms in China, there are few studies on greenhouse gas (GHG) and odor emissions from this composting system. This study focused on GHG and odor emissions from facultative heap composting of four types of livestock manure and revealed the relationship between the gaseous emissions and microbial communities. Results showed that pig, sheep, and cow manure reached high compost maturity (germination index (GI) > 70%), whereas chicken manure had higher phytotoxicity (GI = 0.02%) with higher electrical conductivity and a lower carbon/nitrogen ratio. The four manure types significantly differed in the total GHG emission, with the following pattern: pig manure (308 g CO2-eq·kg-1) > cow manure (146 g CO2-eq·kg-1) > chicken manure (136 g CO2-eq·kg-1) > sheep manure (95 g CO2-eq·kg-1). Bacterium with Fermentative, Methanotrophy and Nitrite respiratory functions (e.g. Pseudomonas and Lactobacillus) are enriched within the pile so that more than 90% of the GHGs are produced in the early (days 0-15) and late (days 36-49) composting periods. CO2 contributed more than 90% in the first 35 d, N2O contributed 40-75% in the late composting period, and CH4 contributed less than 8.0%. NH3 and H2S emissions from chicken and pig manure were 4.8 times those from sheep and cow manure. Overall, the gas emissions from facultative heap composting significantly differed among the four manure types due to the significant differences in their physicochemical properties and microbial communities.

Microbial dynamics and nitrogen retention during sheep manure composting employing peach shell biochar

In this study, the effects of peach shell biochar (PSB) and microbial agent (EM) amendment on nitrogen conservation and bacterial dynamics during sheep manure (SM) composting were examined. Six treatments were performed including T1 (control with no addition), T2 (EM), T3 (EM + 2.5 %PSB), T4 (EM + 5 %PSB), T5 (EM + 7.5 %PSB), and T6 (EM + 10 %PSB). The results showed that the additives amendment reduced NH3 emissions by 6.12%∼32.88% and N2O emissions by 10.96%∼19.76%, while increased total Kjeldahl nitrogen (TKN) content by 8.15-9.13 g/kg. Meanwhile, Firmicutes were the dominant flora in the thermophilic stages, while Proteobacteria, Actinobacteriota, and Bacteroidota were the dominant flora in the maturation stages. The abundance of Bacteroidota and Actinobacteriota were increased by 17.49%∼32.51% and 2.31%∼12.60%, respectively, which can accelerate the degradable organic materials decomposition. Additionally, redundancy analysis showed that Proteobacteria, Actinobacteriota, and Bacteroidota were positively correlated with NO3--N, TKN, and N2O, but a negative correlation with NH3 and NH4+-N. Finally, results confirmed that (EM + 10 %PSB) additives were more effective to reduce nitrogen loss and improve bacterial dynamics.

Mechanisms and effects of novel ammonifying microorganisms on nitrogen ammonification in cow manure waste composting

It is essential to reduce nitrogen losses and to improve nitrogen conversion during organic waste composting because of environmental protection and sustainable development. To reveal newly domesticated ammonifying microorganisms (AM) cultures on the ammonification and nitrogen conversion during the composting, the screened microbial agents were inoculated at 5 % concentration (in weight basis) into cow manure compost under five different treatments: sterilized distilled water (Control), Amm-1 (mesophilic fungus-F1), Amm-2 (mesophilic bacterium-Z1), Amm-3 (thermotolerant bacterium-Z2), and Amm-4 (consortium: F1, Z1, and Z2), and composted for 42 days. Compared to control, AM inoculation prolonged the thermophilic phases to 9-19 days, increased the content of NH4+-N to 1.60-1.96 g/kg in the thermophilic phase, reduced N2O and NH3 emissions by 22.85-61.13 % and 8.45-23.29 %, increased total Kjeldahl nitrogen, and improved cell count and viability by 12.09-71.33 % and 66.71-72.91 %. AM was significantly associated with different nitrogen and microbial compositions. The structural equation model (SEM) reveals NH4+-N is the preferable nitrogen for the majority of bacterial and fungal growth and that AM is closely associated with the conversion between NH3 and NH4+-N. Among the treatments, inoculation with Amm-4 was more effective, as it significantly enhanced the driving effect of the critical microbial composition on nitrogen conversion and accelerated nitrogen ammonification and sequestration. This study provided new concepts for the dynamics of microbial in the ammonification process of new AM bacterial agents in cow manure compost, and an understanding of the ecological mechanism underlying the ammonification process and its contribution to nitrogen (N) cycling from the perspective of microbial communities.

Batch-fed composting of food waste: Microbial diversity characterization and removal of antibiotic resistance genes

The aim of this work was to study the impact of batch-fed strategies on bacterial communities and ARGs in compost. The findings demonstrate that batch-feeding helped maintain high temperatures in the compost pile for an extended period (above 50 °C for 18 days), which in turn facilitated water dissipation. High-throughput sequencing showed that Firmicutes played a significant role in batch-fed composting (BFC). They had a high relative abundance at the beginning (98.64%) and end (45.71%) of compost. Additionally, BFC showed promising results in removing ARGs, with reductions of 3.04-1.09 log copies/g for Aminoglycoside and 2.26-2.44 log copies/g for β_Lactamase. This study provides a comprehensive survey of BFC and demonstrates its potential for eliminating resistance contamination in compost.

Addition of exogenous microbial agents increases hydrogen sulfide emissions during aerobic composting of kitchen waste by improving bio-synergistic effects

The effect of microbial agents (MA) on hydrogen sulfide (H₂S) emissions in the compost is still a controversial issue. This study examined the effects and microbial mechanisms of MA on H₂S emissions during the composting of kitchen waste. The results showed that MA addition can promote sulfur conversion to elevate H₂S emissions by approximately 1.6 ∼ 2.8 times. Structural equations demonstrated that microbial community structure was the dominant driver on H₂S emissions. Agents reshaped the compost microbiome, showing more microorganisms participated in sulfur conversion, and enhanced the connection between microorganisms and functional genes. The relative abundance of keystone species associated with H₂S emissions increased after adding MA. Particularly, the sulfite and sulfate reduction processes were intensified, as evidenced by an increasing in the abundance and pathways cooperation of sat and asrA after MA addition. The outcome provides deeper insights into MA on regulating the mitigation of H₂S emissions in compost.

Effects of cornstalk and sawdust coverings on greenhouse gas emissions during sheep manure storage

Manure covered by organic materials during the storage has shown that it can effectively reduce emissions of greenhouse gases, but few studies have focused on the bacterial communities in manure or the coverage and mechanism responsible for reducing gas emissions. Therefore, this study investigated the impacts and mechanisms of cornstalk and sawdust coverings on greenhouse gas emissions during sheep manure storage. Sheep manure covered by organic material reduced nitrous oxide (N₂O) emissions (42.27%-42.55%) relative to uncovered control through physical adsorption and biological transformation of Acinetobacter, Corynebacterium, Brachybacterium, Dietzia and Brevibacterium. Sheep manure covered by organic materials also increased methane (CH₄) emissions (16.31%-43.07%) by increasing anaerobic zones of coverage. Overall, coverings reduced carbon dioxide equivalent (CO₂eq) by 29.87%-33.60%. Coverings had less effect on the bacterial diversity and community of sheep manure, and the number of bacteria shared by sheep manure and the covering material increased with storage progress, indicating that these bacteria were transferred to the covering materials with gas emissions and moisture volatilization. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) images showed that functional group intensities of the covering materials increased and the fibrous structures became more disordered during the storage period. In general, it was safe to use organic materials as coverages during sheep manure storage, which was conducive to reducing greenhouse gas emissions.

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.

Coupling network of hydrogen sulfide precursors and bacteria in kitchen waste composting

This study was focused on the changes of hydrogen sulfide (H₂S), its precursors, and microorganisms associated with its transformation during the composting process of kitchen waste. The results showed that the content of cysteine (Cys) and methionine (Met) decreased by 32.3 % and 57.5 % respectively, while the content of sulfate (SO₄^2-) changed little during composting. The main release period of H₂S was during the high-temperature period of composting, Cys was its main precursor. Based on network analysis, a total of 15 core genera associated with the conversion of H₂S precursors were identified, and the transformation of the H₂S precursor was mainly influenced by Filomicrobium. Temperature, pH, and TN levels had a positive effect on Filomicrobium. It could find a balance point by controlling these three factors to reduce the production of H₂S.