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Abstract This study investigated the effect of rice straw biochar (RSB) on methane production during mainstream large-scale aerobic composting by using high-throughput sequencing and quantitative PCR. A 55-day large-scale aerobic composting experiment under cyclical forced-turning with aeration was conducted with control (CK) and experimental groups (BC), namely, without and with 10% RSB. The methanogen/methanotroph and microbial community of samples were analyzed by mcrA/pmoA and 16S rRNA/internal transcribed spacer region, respectively. The pore methane concentration had a positive relationship with mcrA and mcrA/pmoA. RSB accelerated methane production, which was reflected by an increase in mcrA. The diversity of bacteria and fungi increased by addition of RSB. Addition of RSB contributed to increasing the RAs of Methanobrevibacter and Methylobacterium. Methanobrevibacter was related to CH 4 production, and Methylobacterium related to CH 4 consumption through the metabolism of methyl material. Thus, the biochar has always increased the diversity of bacteria, including Methanobrevibacter and Methylobacterium. The optimal way to control CH 4 production is to reduce the number of mcrA/pmoA. Meanwhile, RSB contributed to methane production because of its small particle size in this study. The biochar particle size could be further optimized during large-scale aerobic composting process. Highlights • RSB increased the pore methane concentration during aerobic composting. • The mcrA / pmoA ratio is increased by addition of RSB. • RSB increased the richness of Methanobrevibacter and Methylobacterium. • Methanobrevibacter and Methylobacterium showed some correlation with total OM. [ABSTRACT FROM AUTHOR]

This study establishes an optimal mathematical modelling to rationally describe the dynamic changes and spatial distribution of temperature and oxygen concentration in the aerobic composting process using coupling mass-heat-momentum transfer based on the microbial mechanism. Two different conditional composting experiments, namely continuous aeration and intermittent aeration, were performed to verify the proposed model. The results show that the model accurately predicted the dynamic changes in temperature (case I: R 2  = 0.93, RMSE = 1.95 K; case II: R 2  = 0.86, RMSE = 4.69 K) and oxygen concentration (case I: R 2  = 0.90, RMSE = 1.26%; case II: R 2  = 0.75, RMSE = 2.93%) in the central point of compost substrates. It also systematically simulated fluctuations in oxygen concentration caused by boundary conditions and the spatial distribution of the actual temperature and oxygen concentration. The proposed model exhibits good applicability in simulating the actual working conditions of aerobic composting process. [ABSTRACT FROM AUTHOR]

Regulative composting variables, like aeration, turning and additive, are critical factors for low-emission and eco-friendly aerobic composting. The main variables (aeration, turning, and additive) on greenhouse gas (GHG) emission rates and spatial GHG concentrations in the pores of composting piles during the large-scale composting were investigated under a typical trough composting system. An engineering model combined momentum transfer was built to simulate the airflow, temperature, and oxygen concentration distribution; thus, the composting equipment parameters could be preliminarily ensured. The aeration period emitted more carbon dioxide per unit time than the non-aeration period. Over 83% of methane was emitted during nonaeration period. GHG emissions in after-turning period were lower than those both in the nonaeration and aeration periods. Through modeling, momentum lost around 34% by frictional resistance when air flows in pipes. The difference of inlet oxygen velocity distribution of pipe's pores was not over 10%, because high pressure provided by a fan could slow down the frictional resistance along the pipeline. The temperature distribution simulation followed the rules of heat diffusion and convection. The oxygen concentration in piles was transferred by its concentration condition fitting Fick law. Model well simulated the actual condition and composting routine could provide support for composting system design and composting management. Because of the complex condition of large-scale composting, modeling of the airflow simulation on GHG emissions should be further investigated. Image 1 • Aeration promotes GHGs overflow from pores and inhibits the anaerobic environment. • Per unit time, more CO 2 and less CH 4 and emitted during the aeration period. • Model simulated airflow and velocity distribution in the pipes and compost piles. • Momentum lost near 34% by resistance when air flows in pipes by modeling. • Distribution of temperature and oxygen concentration were simulated by model. [ABSTRACT FROM AUTHOR]

[Display omitted] • Membrane coverage technology (CT) was suitable for dairy manure aerobic composting. • CH 4 and N 2 O emission decreased by 99.89% and 60.48% in the CT group. • The total greenhouse gas emission decreased by 70.76% in the CT group. • Intermittent aeration promoted the greenhouse gas emission reduction performance. • Aeration period repaired the water layer to reduce NH 3 emission. In this study, the effects of covering the compost pile with a semi-permeable membrane in combination with intermittent aeration on the gas emissions during aerobic composting from the solid fraction of dairy manure at industrial scale were investigated. A large-scale composting experiment was carried out to compare a membrane-covered (CT) group with a control (CK) group. The results indicated that the CT group could maintain a suitable aerobic and positive micro-pressure environment. The carbon dioxide, methane, nitrous oxide, and ammonia emissions outside the membrane during the aeration interval were reduced by 64.23%, 70.07%, 54.87%, and 11.32%, respectively, compared with that inside the membrane. It was also determined that the methane and nitrous oxide emissions from the CT group were reduced by 99.89% and 60.48% relative to the CK group, confirming that the combined process represented a novel strategy for reducing gas emissions during dairy manure composting. [ABSTRACT FROM AUTHOR]

The objective of the present study was to study the changes in compost particle and its relationship with other physicochemical process during aerobic composting employing 5%, 10%, 20% or 0% biochar. Changes of physicochemical and biological parameters and gases emissions indicated that appropriate biochar addition improved both degradation rate and final degree of the organic matter and simultaneously reduced CO 2 , CH 4 , N 2 O and NH 3 emissions. Beneficial properties like stability and high porosity of biochar could optimize composting environment, accelerate the process of composting and facilitate microbial growth during the thermophilic composting stage, with increases of 1.3 × 10 10 to 1.5 × 10 11 cfu/g. Analysis of microstructure characterization of the changes in compost particle indicated that biochar amended contributed to better degradation of compost particle with smaller sizes and a higher degree of looseness. Ultimately, 10% biochar addition optimized organic matter degradation, while reducing ammonia and greenhouse gas emissions and costs. [ABSTRACT FROM AUTHOR]

• More PB was detected in feces than surrounding soil (SS), while ARB was the opposite. • ARB of AMX dominated in most samples, especially soil, compost, and vegetables. • The composting toilet was faster with less ARB but more PB than open-air composting. • PB and ARB in compost and soil may threaten human health through the food chain. • Multi-drug-resistant bacteria were easier to obtain under the AMX selection pressure. This study evaluated the microbial safety and antibiotic resistance risks of a sustainable ecological farm under large-scale open-air composting (OC) and green composting toilet systems (CT). Samples of livestock manure, compost, soil, vegetables, and rainwater were analysed to determine the best treatment of wastes and risk assessment of land application. Results showed that pathogenic bacteria (PB) in livestock manure was significantly greater than that in the surrounding topsoil, while the distribution of bacteria resistant to amoxicillin (AMX), tetracycline (TC), and amoxicillin-tetracycline (AMX- TC) was the opposite through long-term resistance selection pressure. E. coli and Enterococcus were the dominant pathogens in feces and surrounding soil, respectively, and AMX-resistant bacteria dominated soil, compost, and vegetable samples. Overall, while OC may significantly increase antibiotic resistance and effectively remove fecal PB, CT offers faster consumption with greater antibiotic resistant bacteria (ARB) removal but more PB. Moreover, PB and ARB were concentrated in mature compost, soil in planting areas, vegetables, and rainwater. In farm soil and vegetables, AMX-resistant and AMX-TC-resistant bacterial communities displayed similar composition. These findings may explain the main pathways of PB transmission, migration and accumulation of ARB in farms, and the potential risks to human health through the food chain. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Amoxicillin (AMX) alters nitrogen transformation and release relative to control. • AMX raised NH 4 +-N content and lowered NO 2 −-N and NO 3 −-N content versus control. • AMX delays compost maturation and alters bacterial community makeup and succession. • AMX reduced Firmicutes, Bacteroidetes and improved Proteobacteria relative abundance. • AMX inhibits ammoniated and ammonia-oxidizing bacteria, boosts denitrifying bacteria. Abstract This study systematically analyzed the effects of amoxicillin (AMX) on the nitrogen transformation and its corresponding functional bacterial communities by conducting two aerobic composting experiments, and AMX impact on bacterial community succession was also evaluated. It provides theoretical and methodological support for harmless composting treatment of large quantities of manure containing AMX in China and for the high-quality compost products. The results showed that AMX exerted several effects on basic physicochemical and biological compost parameters. Notably, temperature changes typically accompanying compost maturation were delayed in AMX compost, reflecting altered compost maturation kinetics and bacterial community structure. Moreover, relative to control, AMX inhibited growth and reproduction of dominant bacterial phyla Firmicutes and Bacteroidetes, with respective reductions of 17.8–26.1% and 0–7.76% in relative abundance (RA) and significantly increased Proteobacteria RA by 1.9–24.8%. Thus, AMX altered both compost bacterial community structure and succession. From the perspective of various nitrogen content changes, AMX has a significant effect on nitrogen conversion and release. Simultaneously, AMX may inhibit ammoniated and ammonia-oxidizing bacterial activity, while significantly increasing the RA of denitrifying bacteria. Indeed, during early composting with AMX, the RA of denitrifying bacteria was 1361.9–1435.0% of control, highlighting differences in nitrogen transformation and release between groups. [ABSTRACT FROM AUTHOR]

Bacteria play an important role in organic matter degradation and maturity during aerobic composting. This study analyzed composting with or without a membrane cover in laboratory-scale aerobic composting reactor systems. 16S rRNA gene analysis was used to study the bacterial community succession during composting. The richness of the bacterial community decreased and the diversity increased after covering with a semi-permeable membrane and applying a slight positive pressure. Principal components analysis based on operational taxonomic units could distinguish the main composting phases. Linear Discriminant Analysis Effect Size analysis indicated that covering with a semi-permeable membrane reduced the relative abundance of anaerobic Clostridiales and pathogenic Pseudomonas and increased the abundance of Cellvibrionales . In membrane-covered aerobic composting systems, the relative abundance of some bacteria could be affected, especially anaerobic bacteria. Covering could effectively promote fermentation, reduce emissions and ensure organic fertilizer quality. [ABSTRACT FROM AUTHOR]

In this study, 100 mg/kg of amoxicillin (AMX) was added to pig manure during aerobic composting using a laboratory-scale reactor system, for better understanding the degradation of AMX and its potential risks. Qualitative and quantitative analysis of AMX and its main degradation products (DPs) were then conducted using solid phase extraction combined with high performance liquid chromatography-tandem mass spectrometry. Additionally, hydrolysis testing was performed to monitor DPs produced from AMX degradation under various controlled conditions. The results showed that AMX was unstable in compost and rapidly degraded into AMX penicilloic acid, AMX penilloic acid and AMX diketopiperazine, which all eventually degraded, leaving a structurally simple and stable end product, 3-(4-hydroxyphenyl) pyrazin-2-ol, which appeared to be nonallergenic and less toxic than DPs generated earlier in the composting process. Besides, AMX was more unstable and more apt to generate multiple DPs in alkaline conditions than in acidic or neutral conditions or in ultrapure water, while pH exerted a larger effect on AMX degradation than did divalent metal ions (Cu 2+ and Zn 2+ ). This study provides technical and methodological support to better achieve AMX residual treatment and to evaluate the safety of AMX DPs produced in huge quantities in compost in China. [ABSTRACT FROM AUTHOR]

[Display omitted] • Micro-aerobic conditions improved compost product quality. • Micro-aerobic conditions were conducive to DOC generation and retention. • Aromatic polymerization was greater under micro-aerobic than static conditions. • Mycothermus dominated the composting process. • The proportion of soil saprotrophs was 5.18% higher after micro-aerobic composting. This study investigated the effects of micro-aerobic conditions on fungal community succession and dissolved organic matter transformation during dairy manure membrane-covered composting. The results showed that lignocellulose degradation in the micro-aerobic composting group (AC: oxygen concentration < 5 %) was slower than that in the static composting group (SC: oxygen concentration < 1 %), but the dissolved organic carbon in AC was greatly increased. The degree of aromatic polymerization was higher in AC than in SC. But the carboxyl carbon and alcohol/ether biodegradations were faster in SC than in AC, which promoted carbon dioxide and methane emissions, respectively. The relative abundances of pathogenic and dung saprotrophic fungi in AC were 44.6 % and 10.59 % lower than those in SC on day 30, respectively. Moreover, the relative abundance of soil saprotrophs increased by 5.18 % after micro-aerobic composting. Therefore, micro-aerobic conditions improved the quality of compost products by influencing fungal community evolution and dissolved organic matter transformation. [ABSTRACT FROM AUTHOR]

A revised oxygen uptake rate model that considers the specific characteristics of the substrate and the temperature dependence of microbial growth for pig manure–wheat straw aerobic composting was established. The model validation results showed good agreement with experimental data. The model’s accuracy, in terms of a lower relative error and fewer deviations of the oxygen uptake rate, was improved, but the oxidation of the remaining carbon requires further study. Sensitivity analyses were performed to simulate different composting processes and to explore potential engineering applications to the improvement of composting. The specific growth rate constant of the composting mixture was 0.42 h −1 . Enhanced aeration in the thermophilic phase is suggested for a soluble-rich substrate. Reducing insoluble substrate will help shorten composting period and improve the product’s stability. The smaller the particle size, the better the composting efficiency when air permeability is guaranteed. The optimal ambient temperature of the compost was 21–35 °C. These findings provide a theoretical basis that can inform the design of an economical operation strategy for aerobic composting. [ABSTRACT FROM AUTHOR]

Characterization of the dynamic structure of composting particles may facilitate our understanding of the mechanisms of organic matter degradation during pig manure–wheat straw aerobic composting. In this study, changes in the size, shape, pores, chemical compositions, and crystal structures of pig manure particles during composting were investigated. The results showed that the median diameter ( D 50 ) decreased exponentially, while the particle aspect ratio and sphericity were unchanged, suggesting that particles were degraded uniformly along different radial directions. Pores had a mean diameter of 15–30 μm and were elliptical. The particle porosity increased linearly mainly because of hemicellulose degradation. Furthermore, the influence of particle structure variation on the first order rate constant ( k ) of organic matter degradation was corrected, which may facilitate the optimization of operation conditions. The k value was proportional to the reciprocal of D 50 according to the specific surface area of particles, and it decreased with increased porosity due to the stabilized chemical compositions and crystal structures of particles. However, the applicability of these data to other composting materials should be verified. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biochar can promote the degradation process of TCs during aerobic composting. • ARGs were transferred from Firmicutes to Actinobacteria at the phylum level. • The RA of ARGs in the biochar group was reduced by 16.83 ± 4.10%. • Biochar facilitates the removal of sav186 6, ImrD , efrA , tetB(P), and tetL. This study investigated the effect of biochar on antibiotics and antibiotic resistance genes (ARGs) during aerobic composting of pig manure. First, the composition and content of antibiotics in the manure were determined qualitatively and quantitatively. Biochar promoted the degradation of these antibiotics (oxytetracycline, chlortetracycline, and tetracycline). The relative abundance (RA) of antibiotic-resistant bacteria carrying ARGs accounted for about 29.32% of the total bacteria. Firmicutes and Actinomycetes were dominant phylum-level bacteria at the early and late stages of composting, respectively. Biochar decreased the total RA of ARGs by 16.83%±4.10%. tetW and tetL , closely related to tetracycline resistance, were significantly diminished during aerobic composting, and biochar was able to promote this removal. Biochar enhanced RAs of Mycobacterium tuberculosis kasA mutant. RAs of ARGs related to antibiotic efflux pumps, such as baeS and arlS , remained at a high level. Conclusively, biochar promotes degradation of antibiotics and removal of ARGs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effects of different membranes covering in aerobic composting were investigated. • Covering membranes can retain heat and increase volatile solid degradation. • Different membranes have different emission reduction effects on gas emissions. • The bacterial community was changed by covering the membrane in composting. The effects of the functional membrane covering on the gas emissions and bacterial community during dairy cow manure aerobic composting were investigated. A lab-scale aerobic composting experiment was conducted with the control group (CK), Gore group (Gore), and ZT group (ZT), namely, without and with two functional membranes. Covering the functional membrane retained heat and improved the seed germination index in Gore and ZT groups. Compared with the CK group, the Gore membrane decreased NH 3 and N 2 O emissions by 11.77% and 26.40%, respectively. The ZT membrane decreased N 2 O and CO 2 emissions by 68.44% and 1.56%, respectively. The Gore and ZT membranes decreased the global warming potential by 16.97% and 53.41%, respectively. Moreover, Covering the two functional membranes improved the Actinobacteria relative abundance and were conducive to the degradation of volatile solid. Altogether, membrane-covered aerobic composting is an important technology for the resource utilization of organic waste. [ABSTRACT FROM AUTHOR]

[Display omitted] • FMC increased pile temperature and promoted compost maturity. • FMC decreased NH 3 and N 2 O emissions by 7.34% and 26.27%, respectively. • Micro-positive pressure promoted aerobic composting and decreased gas emissions. • FMC up-regulated the amoA and nosZ genes and down-regulated the nirK and nirS genes. • FMC clearly affected the evolution of nitrogen and related functional genes. The effects of functional membrane covering (FMC) on nitrogen transformation and related functional genes during aerobic composting were investigated by performing a comparable experiment. The FMC increased the pile temperature, promoted compost maturity, and decreased nitrogen loss. The FMC reduced NH 3 and N 2 O emissions by 7.34% and 26.27%, respectively. The water film and the micro-positive pressure environment under the membrane effectively prevented NH 3 escaping. The FMC up-regulated the amoA gene copy number (promoting NH 3 /NH 4 + oxidation). The reduction of N 2 O emission by the FMC was mainly related to denitrifying genes (nirK, nirS, and nosZ). The FMC down-regulated the nirK and nirS gene copy numbers, but up-regulated the nosZ gene copy number. Pearson correlation analysis indicated that the functional membrane characteristics and differences between the composting pile environments caused by the FMC significantly affected the nitrogen forms and the related functional genes. The FMC strongly decreased nitrogen emissions and therefore conserved nitrogen. [ABSTRACT FROM AUTHOR]

• nirK and nosZ are the most abundant denitrifying gene in samples. • PBB reduced ammonia-oxidizing species' abundance: Nitrosomonas & Nitrosococcus. • PBB significantly affected nitrogen metabolism (KO00910) (p < 0.05). • PBB inhibited the activity of glutamate dehydrogenase to reduce NH 3 emission. To investigate the emission mechanism of ammonia (NH 3) and nitrous oxide (N 2 O) during aerobic composting and the influence of powder bamboo biochar (PBB) on this process, this paper conducted a systematic study on the nitrogen-transforming functional microbial community, including functional genes, microbial structure and metabolism pathways. PBB reduced N 2 O and NH 3 emissions by 1.25%–8.72% and 10.4%–11.8%, respectively. The quantitative PCR results indicated that the reduced N 2 O emission by PBB were mainly related to denitrifying genes (nirS , nirK , nosZ , and narG). The metagenome results demonstrated that Nitrosococcus was the main genus that could oxidize ammonia to nitrite decreased by PBB. The PBB significantly affected the nitrogen metabolism pathway, reduced the activity of glutamate dehydrogenase to inhibit the formation of NH 4 + to reduce NH 3 emission. The higher N 2 O emission in the control group was also related to the higher relative contents of hydroxylamine reductase and nitrite reductase. [ABSTRACT FROM AUTHOR]

In order to study the effects of intermittent aeration on greenhouse gas emissions and bacterial community succession during membrane-covered aerobic composting, a large-scale aerobic composting experiment was carried out. Two different aeration intervals designed to maintain the temperature of the compost was in 50–65 °C. The control group and experimental group were set to 10 min–10 min (on-off) and 10 min–30 min (on-off), respectively. The results indicated that the emissions of methane and nitrous oxide from the outside of the membrane in the control group were 9.68% and 47.10% less than those in the experimental group. And the global warming potential was 9.77% less than that in the experimental group. Wilcoxon rank-sum test result indicated that Tenericutes was a significantly different phylum between the two groups and played an important role in cellulose degradation. Redundancy analysis indicated that C/N had the greatest influence on the distribution of the bacterial community. It also found that Pseudogracilibacillus and Tepidimicrobium were significantly correlated with nitrous oxide and carbon dioxide emission rates, respectively. Therefore, adjusting aeration interval time during the membrane-covered aerobic composting could be a useful strategy for limiting greenhouse gas emissions and effecting bacterial community structure. Image 1 • The aeration method of 10 -10 can effectively reduce greenhouse gas emissions. • C/N had the greatest influence on the distribution of bacterial community. • Tenericutes was significantly different phylum between the two groups. • Pseudogracilibacillus was positively correlated with N 2 O emission rate. • Tepidimicrobium was negatively correlated with CO 2 emission rate. [ABSTRACT FROM AUTHOR]