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Resistance genes have been identified as emerging pollutants due to their ability to rapidly spread in the environment through horizontal gene transfer (HGT). Microbial community serves as the pivotal factor influencing the frequency of HGT during manure composting. However, the characteristics of HGT in microbial community from different types of manure were unclear. Therefore, this study aimed to evaluate the potential risk of HGT in bacterial community through the co-composting of chicken manure and pig manure in different proportions. The experimental results showed that the abundance of sulfonamide antibiotic resistance genes and integrase genes was higher during pig manure composting than those during chicken manure composting. In addition, the addition of pig manure also increased resistance genes abundance during chicken manure composting. These results suggested that the potential HGT risk was greater during pig manure composting. Furthermore, microbial analysis of co-composting suggested that bacterial community of pig manure was more competitive and adaptable than that of chicken manure. Ultimately, statistical analysis indicated that compared to chicken manure composting, the potential ability of HGT was greater during pig manure composting. This study provided the vital theoretical support and scientific guidance for mitigating the HGT risk during manure composting. [Display omitted] • The pig manure addition increased sul3, zntA and intⅠ1 abundance in chicken manure. • The bacterial community of pig manure was more competitive and adaptable. • The potential genes spread risk was greater during pig manure composting. • The structure and response of bacterial community determined gene transfer ability. [ABSTRACT FROM AUTHOR]

Humic acid (HA) from different organic solid waste (OSW) compost has been shown good adsorption properties for phenanthrene. However, the raw material of HA can affect its structure, resulting in differences in adsorption capacity. Therefore, this study focused on the adsorption characteristics of phenanthrene by HA from different OSW compost. In this work, chicken manure (CM), rice straw (RS) and lawn waste (LW) were selected as sources of composted HA. The adsorption mechanism of HA from different OSW compost were revealed through analytical techniques including three-dimensional fluorescence spectroscopy (EEM), two-dimensional correlation spectroscopy (2DCOS), and Fourier-transform infrared spectroscopy (FTIR). The results suggested that HA from LW compost had a better adsorption affinity for phenanthrene because of its more complex fluorescent component, where C1 as a simple component determined the adsorption process specifically. Furthermore, after HA from LW compost adsorbed phenanthrene, the increase in aromatic –COOH and –NH was the main reason for fluorescence quenching. These results indicated that HA from LW compost had better adsorption effect for phenanthrene. The results of this study were expected to provide a selection scheme for the control of phenanthrene pollution and environmental remediation. [Display omitted] • Fluorescence was excited by the adsorption of humic acid from chicken manure compost to phenanthrene. • Fluorescence was quenched by the adsorption of humic acid from rice straw and lawn waste compost to phenanthrene. • Aromatic –NH and –COOH contributed to fluorescence quenching of humic acid from lawn waste compost. • Humic acid from lawn waste compost had the better adsorption affinity for phenanthrene. [ABSTRACT FROM AUTHOR]

Mobile genetic elements (MGEs) play critical roles in transferring antibiotic resistance genes (ARGs) among different microorganisms in the environment. This study aimed to explore the fate of MGEs during chicken manure (CM) and bovine manure (BM) composting to assess horizontal transfer risks of ARGs. The results showed that the removal efficiency of MGEs during CM composting was significantly higher than that during BM composting, because the potential host bacteria of MGEs were eliminated largely during CM composting. Meanwhile, these potential host bacterial communities are significantly influenced by pH, NH 4 +, NO 3 − and total N, which can be used to regulate host bacterial communities to remove MGEs during composting. Projection pursuit regression further confirmed that composting can effectively reduce the horizontal transfer risk of ARGs, especially for CM composting. These results identified the critical roles of host bacterial communities in MGEs removal during composting of different animal manures. Image 1 • The removal rate of MGEs was higher in CM composting than that in BM composting. • The potential host bacteria of MGEs were almost eliminated during CM composting. • The pH, NH 4 +, NO 3 − and total N can regulate MGEs removal during composting. • Fresh CM was confirmed to have greater risk for HGT in comparison with BM. Host bacterial community of MGEs determines the risk of horizontal gene transfer during composting of different animal manures. [ABSTRACT FROM AUTHOR]

• Chemical structure of HLS from different composting is characterized. • The transformation mechanism of components is identified by hetero-2DCOS. • The microenvironment is reshaped by MnO 2. • The role of MnO 2 in the abiotic and biotic pathways of HLS formation is identified. The humic-like substances (HLS) are proposed to be formed by biotic and abiotic pathways. The abiotic pathways were neglected in existed composting studies. The present study aims to accelerate the abiotic pathways, and to investigate how MnO 2 drives the HLS transformation via changing the contribution of abiotic and biotic pathways during composting with different materials. Parallel factor analysis model (PARAFAC), hetero two-dimensional correlation spectra (hetero-2DCOS) and variance partitioning were used to identify the effects of MnO 2 on the formation of humic acid (HA) and fluvic acid (FA) during composting of chicken manure (CM) and corn straw (CS). The addition of MnO 2 could change the structures of HLS during CS and CM composting, mainly promoting the formation of complex components in HA and FA during CS composting, as well as the complex components of FA during CM composting. Meanwhile, the addition of MnO 2 could reshape the microbial ecology, which enhanced the correlation between microbes and complex components formation during composting, especially in CM composting. Variance partitioning showed that both abiotic and biotic pathways were stimulated in conversion of HLS components after adding MnO 2 during CS composting, especially for the abiotic pathways. During CM composting, the MnO 2 promoted biotic effects on the conversion of HLS components. Above all, the addition of MnO 2 could stimulate pathways of biotic, abiotic or both of them to improve the humification degree of HLS by changing microbial ecology, which could be a promising way for promoting the application value of composting products. [ABSTRACT FROM AUTHOR]

Nitrate can stimulate microbes to degrade aromatic compounds, whereas humic acid (HA) as a high molecular weight aromatic compound, its formation may be affected by elevated nitrate during composting. Therefore, this study is conducted to determine the effect of elevated nitrate on HA formation. Five tests were executed by adding different nitrate concentrations to chicken manure composting. Results demonstrate that the concentration of HA in treatment group is significantly decreased compared with control group ( p  < 0.05), especially in the highest nitrate concentration group. RDA indicates that the microbes associated with HA and environmental parameters are influenced by elevated nitrate. Furthermore, structural equation model reveals that elevated nitrate reduces HA formation by mediating microbes directly, or by affecting ammonia and pH as the indirect drivers to regulate microbial community structure. [ABSTRACT FROM AUTHOR]

Metal pollution caused by industrial waste accumulation is a long-term and far-reaching problem. Humin (HM), as a highly condensed organic component insoluble in alkaline or water solution, is often discarded as humic acid industrial waste. However, the abundant active functional groups in HM reported by some researches make it possible for HM to remove metals. In this study, a waste reuse strategy was proposed to reduce the pressure of industrial metal pollution on the environment. HM was obtained from lignite waste residue. Scanning electron microscopy, energy spectrum and Fourier infrared spectroscopy, combined with the adsorption models were employed to reveal the mechanism of HM adsorption. The results showed that HM had multiple adsorption mechanism and high biological stability. The adsorption capacity of HM to Zn2+ and Pb2+ were 194.88 mg/g and 289.59 mg/g respectively. HM adsorbed Zn2+ mainly by physical multilayer adsorption. And the adsorption of Pb2+ by HM was mainly a monolayer chemical reaction, which depended on its active functional groups and the exchange of valence electrons. Notably, HM could simultaneously remove Pb2+ and Zn2+ and almost did not affect its original adsorption capacity to single ions. These results will provide a new strategy for the treatment of metal pollution in the future and alleviate the pressure of multiple metal pollution of the environment. [Display omitted] • Humin (HM) from waste absorbed 194.88 mg/g Zn2+ and 289.59 mg/g Pb2+ respectively. • HM had multiple adsorption mechanism and high biological stability. • HM bonded Pb2+ via monolayer adsorption such as valence electron exchange. • HM bonded Zn2+ via multilayer adsorption such as physical filling. • HM could simultaneously treat many kinds of metal pollution. [ABSTRACT FROM AUTHOR]

A study was conducted to determine the fluorescence characteristics of various molecular weight (MW) fractions of dissolved organic matter (DOM) derived from different composts based on fluorescence regional integration (FRI) and parallel factor (PARAFAC) modeling of excitation-emission matrix (EEM) fluorescence spectra. The significant differences in the locations of EEM peaks indicated that there were differences in the molecular structures of the MW >5 kDa fraction and the other fractions. FRI indicated that the degree of humification increased with increasing MW for all of the MW fractions, except for the MW >5 kDa fraction, suggesting that FRI was not suitable for analyzing MW fractions with differences in their molecular structures. PARAFAC modeling resulted in three components for the MW >5 kDa fraction and two components for the other MW fractions. Red-shifting occurred in components 1 (Microbial Humic-like) and 2 (Terrestrial Humic-like) as the MW increased. And component 3 was categorized as a protein-like substance. PARAFAC modeling of the MW fractions can isolate more components and resolve more fluorophores than can DOM analysis. [ABSTRACT FROM AUTHOR]

This study was conducted to assess the abundance, incidence and diversity of the culturable phosphate-solubilizing bacteria (PSB) community during different organic wastes composting. The key PSB affecting different phosphorus (P) fractions and their relationship with environmental variables were analyzed by redundancy analysis (RDA). The results showed that there were distinct differences in amounts, incidence and community composition of PSB for the composts from different sources. Regression analysis demonstrated significant corrections between the density and incidence of PSB and pH, temperature, OM and DOC/DON. Most of culturable PSB showed high percentages of identity with the phyla of Firmicutes and Proteobacteria . There were thirteen key PSB correlated closely ( p < 0.05) with different P fractions variation. Conclusively, we suggested a process control method to regulate the distribution of P fractions during composting based on the relationship between the key PSB and P fractions as well as environmental parameters. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) has important impacts on the transportation of antibiotics through chemical and biological processes in composting. The interaction between DOM and antibiotics is reciprocal. The interaction between DOM ligands and antibiotics could be characterized based on a technique combining parallel factor analysis (PARAFAC) and microbial community structure analysis. However, PARAFAC cannot reveal the dynamic changes in each DOM peak in one PARAFAC component under antibiotic stress. In this study, two-dimensional correlation spectroscopy (2DCOS) combined with PARAFAC and bacterial community diversity analyses were employed to reveal the effects of oxytetracycline (OTC) stress and the key microorganisms on the transformation of different fluorescent peaks from DOM PARAFAC components during chicken manure composting. The results showed that OTC inhibits the transformation between DOM PARAFAC components by inhibiting the core microbial activities involved in the transformation of DOM components. Protein-like components (C1 and C2) were more sensitive to OTC residue, and components with a high humification degree promoted the degradation of OTC. The interaction between special DOM PARAFAC components and certain bacteria affects the degradation of OTC. The DOM PARAFAC components A2(C1), B1(C2), B2(C2) and Z1(C4) enhanced OTC degradation by stimulating the genera Pseudomonas , Glycomyces and Hyphomicrobium. With these promising results, the true effect of DOM PARAFAC components on the degradation of OTC can be revealed, which is helpful for addressing antibiotic contamination to improve the bioavailability of compost products. [Display omitted] • Multiple spectral analytical techniques are used to reveal dissolved organic matter. • Oxytetracycline can inhibit the fate of dissolved organic matter components. • Protein-like components are more sensitive to oxytetracycline residue in composting. • Humic-like components can promote the degradation of oxytetracycline in composting. [ABSTRACT FROM AUTHOR]

[Display omitted] • Significant difference in nitrogen conversion of different composting. • Functional keystone involved in the nitrogen conversion were identified. • Change in abundance of functional keystone was limited during composting. • Composting microenvironment drove functional keystone. In this study, nitrogen transformation of chicken manure (CM) and cattle dung (CD) during composting was analyzed and its related functional keystones were identified. The results showed that chicken manure showed more severe nitrogen conversion during composting. The main N conversion factors in cattle dung were nitrite nitrogen (NO 2 –-N) and ammonium nitrogen (NH 4 +-N), while the main N conversion factors in chicken manure were NH 4 +-N and nitrate nitrogen (NO 3 –-N). The nitrogen-transforming bacterial community in chicken manure was more diverse. Variations in functional keystone abundances in cattle dung tended to be confined to the cooling and maturation periods, whereas changes in chicken manure persisted throughout the composting process. Environmental factors affected the functional keystones of nitrogen transformation. This study may provide directions for regulating nitrogen conversion in animal manure composting. [ABSTRACT FROM AUTHOR]

Black carbon (BC) exports huge amounts of its derived DOM from terrestrial ecosystems annually through a variety of ways (i.e., erosion or runoff migration). The pyrolytic feedstock type and temperature resulted in DOM derived from highly condensed aromatic and non-aromatic BC. However, the behaviors of low aromatic BC-derived DOM at diverse leaching time are poorly understood. In this work, low aromatic BCs were prepared by pyrolysis corn straws at 250 °C, 350 °C and 450 °C. Extraction experiments for four leaching time (6 h, 10 h, 15 h and 21 h) were set up to simulate BC-derived DOM generative process in nature. The phytotoxicity of BC-derived DOM was evaluated via germination index (GI). Spectral characteristics were discussed to analyze the phytotoxicity variations of fluorescence components composition at different time, including the excitation-emission matrix-parallel factor, two-dimensional correlation spectra and Fourier transform infrared spectroscopy. The results suggested that low aromatic BC-derived DOM might contain aromatic phenolic compounds. A longer time contributed to accumulate the complex, hard-to-use organic matters, leading to lower GI. These results would supplement the dynamic spectral characteristics of low aromatic BC-derived DOM and its environmental risks during the leaching process. [Display omitted] • The dissolved organic matter of black carbon (BC) degraded with the leaching time. • BC derived dissolved organic matter (DOM) contained 0.95–5.87 mg/L phenols. • Leaching time promoted the dissolution of phenolic compounds from low-aromatic BC. • The accumulation of phenolic compounds in BC-derived DOM inhibited root growth. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nine mature composts from different sources in China were investigated. [•] Analyze the distribution of MW fractions and BOD5 of DOM among the samples. [•] Identify the correlation of BOD5 with the concentration of MW fractions. [•] Describe the feasibility of BOD5 as a biodegradable indicator for DOM from compost. [Copyright &y& Elsevier]

Highlights: [•] Eight mature composts from different sources in China were investigated. [•] Analyze the characteristics of fluorescence spectroscopy of dissolved organic matter (DOM) among the compost samples. [•] Characterize the correlation of fluorescence parameters of DOM. [•] Identify humification degree of DOM using hierarchical cluster analysis (HCA) and projection pursuit regression (PPR). [ABSTRACT FROM AUTHOR]

[Display omitted] • Mink manure compost had serious nitrogen mineralization. • Inoculants could reduce nitrogen mineralization during mink manure composting. • Inoculants increased bioavailable organic nitrogen (BON) content. • Inoculants affected microbial abundance related to BON. Mink manure is one of the high nitrogenous wastes, which can easily cause nitrogen mineralization during composting, resulting in low resource reutilization. However, there are few studies on the resource utilization of mink manure. Therefore, this study investigated the effects of functional microbial (bacterial and actinomycetes agents) inoculation on nitrogen mineralization during mink manure composting. Results suggested that the inoculum, especially actinomycetes agents, could increase organic nitrogen and bioavailable organic nitrogen (BON) content. Principal component analysis and Random Forest model demonstrated that the inoculants increase the abundance of microorganisms that positively correlated with BON, decrease the microorganisms that negatively correlated with BON. Consequently, the inoculation of functional microbial agents could effectively reduce nitrogen mineralization and improve composting quality. Therefore, this study provided theoretical and technical support for optimizing mink manure composting, promoting the resource utilization of high nitrogen wastes. [ABSTRACT FROM AUTHOR]

Abstract: The physicochemical properties of eight hazardous waste samples (S1, S2, S3, S4, S5, S6, S7 and S8) obtained from Heilongjiang Province were analyzed to assess the suitability of landfill directly. The results showed that the wet content of eight samples was according with the landfill standards. However, some parameters of the samples S1, S2, S5 and S6 were not up to the standards. In addition, the Fe, Mn, Zn, Ni, Cr, and Be content in samples S1 and S5 exceeded the landfill standard limit. The sources of heavy metals were identified by analysing the correlation of the Zn, Mn and Ni concentration in different samples. The result showed that the correlation coefficient of the Zn, Mn and Ni concentration exhibited a significant level, which indicated that the metal Zn, Mn and Ni might originate the same source. The inorganic fluoride content in all samples did not exceed the landfill control standard, whereas the cyanide concentration was as 244.80∼2 692.76 times as the control limits except S1. In addition, benzene series were detected in some samples except S6 and S7, indicating that these samples needed pre-treatment before landfill. [Copyright &y& Elsevier]

[Display omitted] • Microbial metabolism drives the transformation of organic matter in composting. • Microhabitat factors directly affect microbial metabolism. • Regulating composting parameters may realize carbon fixation with high efficiency. • Utilize functional materials could stabilize formed humus components. Transforming organic waste into stable carbon by composting is an eco-friendly way. However, the complex environment, huge microbial community and complicated metabolic of composting have limited the directional transformation of organic carbon, which is also not conducive to the fixation of organic carbon. Therefore, this review is based on the formation of humus, a stable by-product of composting, to expound how to promote carbon fixation by increasing the yield of humus. Firstly, we have clarified the transformation regularity of organic matter during composting. Meanwhile, the microhabitat factors affecting microbial catabolism and anabolism were deeply analyzed, in order to provide a theoretical basis for the micro habitat regulation of directional transformation of organic matter during composting. Given that, a method to adjust the directional humification and stabilization of organic carbon has been proposed. Hoping the rapid reduction and efficient stabilization of organic waste can be realized according to this method. [ABSTRACT FROM AUTHOR]

Heavy metal pollution was the main risk during livestock manures composting, in which microorganisms played a vital role. However, response strategies of microbial community to heavy metals stress (HMS) remained largely unclear. Therefore, the objective of this study was to reveal the ecological adaptation and counter-effect of bacterial community under HMS during chicken manures composting, and evaluating environmental implications of HMS on composting. The degradation of organic matters (more than 6.4%) and carbohydrate (more than 19.8%) were enhanced under intense HMS, suggesting that microorganisms could quickly adapt to the HMS to ensure smooth composting. Meanwhile, HMS increased keystone nodes and strengthened significant positive correlation relationships between genera (p < 0.05), indicating that bacteria resisted HMS through cooperating during composting. In addition, different bacterial groups performed various functions to cope with HMS. Specific bacterial groups responded to HMS, and certain groups regulated bacterial networks. Therefore, bacterial community had the extraordinary potential to deal with HMS and guarantee chicken manures composting even in the presence of high concentrations of heavy metals. [Display omitted] • Composting microorganisms could quickly adapt to heavy metals stress. • Microorganisms coped with heavy metals stress through cooperating. • Different bacterial groups performed various functions to cope with metals stress. • Chicken manures composting could be guaranteed even under intense metals stress. [ABSTRACT FROM AUTHOR]

Composting is a biodegradation and transformation process that converts lignocellulosic biomass into value-added products, such as humic substances (HSs). However, the recalcitrant nature of lignocellulose hinders the utilization of cellulose and hemicellulose, decreasing the bioconversion efficiency of lignocellulose. Pretreatment is an essential step to disrupt the structure of lignocellulosic biomass. Many pretreatment methods for composting may cause microbial inactivation and death. Thus, the pretreatment methods suitable for composting can promote the degradation and transformation of lignocellulosic biomass. Therefore, this review summarizes the pretreatment methods suitable for composting. Microbial consortium pretreatment, Fenton pretreatment and surfactant-assisted pretreatment for composting may improve the bioconversion process. Microbial consortium pretreatment is a cost-effective pretreatment method to enhance HSs yields during composting. On the other hand, the efficiency of enzyme production during composting is very important for the degradation of lignocellulose, whose action mechanism is unknown. Therefore, this review describes the mechanism of action of lignocellulase, the predominant microbes producing lignocellulase and their related genes. Finally, optimizing pretreatment conditions and increasing enzymatic hydrolysis to improve the quality of composts by controlling suitable microenvironmental factors and core target microbial activities as a research focus in the bioconversion of lignocellulose during composting in the future. • The pretreatment destroys the structure of refractory lignocellulose. • Combined pretreatment and composting have a synergistic effect on HSs formation. • The key roles of lignocellulase during composting have been confirmed. • Directional control HSs formation has been proposed. [ABSTRACT FROM AUTHOR]

Municipal solid waste (MSW) compost contains a significant amount of humic substances. In this study, the compost consisted of residual MSW with the metal, plastic and glass removed. In order to enhance degradation processes and the degree of composting humification, complex microorganisms (Bacillus casei, Lactobacillus buchneri and Candida rugopelliculosa) and ligno-cellulolytic (Trichoderma and White-rot fungi) microorganisms were respectively inoculated in the composting process. During the MSW composting, humic acid (HA) was extracted and purified. Elements (C, N, H, O) and spectroscopic characteristics of the HA were determined using elementary analyzer, UV, Fourier transform infrared (FTIR), and fluorescence spectroscopy. The elements analysis, UV, FTIR and fluorescence spectra all led to the same conclusion, that is inoculations with microbes led to a greater degree of aromatization of HA than in the control process (CK) with no inoculation microbes. This indicated that inoculation with microbes in composting would improve the degree humification and maturation processes, in the following order: lingo-cellulolytic>complex microorganisms>CK. And mixed inoculation of MSW with complex microorganisms and lingo-cellulolytic during composting gave a greater degree of HA aromatization than inoculation with complex microorganisms or lingo-cellulolytic alone. But comparing with the HA of soil, the HA of MSW compost revealed a lower degree of aromatization. [Copyright &y& Elsevier]

[Display omitted] • Combined addition enhanced correlations of aromatic amino acids and humic acid. • Combined addition increased the number of functional microorganisms (up to 41). • Shikimic acid pathway played a vital role in humic acid formation. The final products of shikimic acid pathway, aromatic amino acids (AAA), can be used as humic acid (HA) precursors. Therefore, the aim of this study was to explore the contribution of shikimic acid pathway on the formation of HA during composting. Four composting treatments were carried out in this study, including the control, biochar addition, montmorillonite addition, biochar and montmorillonite combined addition. The results showed that the correlations between AAA and HA were enhanced during combined addition composting, and functional microorganisms involved in the shikimic acid pathway increased. In addition, random forest model suggested that 63.3% of the top 30 genera contributing to the HA formation were functional microorganisms involved in the shikimic acid pathway, which fully proved the critical role of shikimic acid pathway. Therefore, this study provided a new perspective for revealing the crucial factors that promoted the formation of HA during composting. [ABSTRACT FROM AUTHOR]

[Display omitted] • Recycle P from sludge by composting technology to reduce P pollution. • Adjusting the initial carbon and phosphorus ratio is beneficial to sludge composting. • The recovery rate of phosphorus in sludge compost was improved. • The conversion and content of available phosphorus were increased. • It was beneficial to the expression of P gene and increased the solubility of P. Phosphorus is an essential nutrient for organisms, but excessive amounts can cause environmental pollution. Phosphorus-rich sludge can solve the problem of the loss of phosphorus resources after resource treatment. This study aimed to explore the mechanism between phosphorus functional genes and phosphorus availability by regulating the initial carbon and phosphorus ratio in sludge compost, with the goal of improving sludge phosphorus recovery efficiency. The results showed that a higher initial carbon and phosphorus ratio can promote the conversion of phosphorus from sludge to Olsen phosphorus and increase the contents of Water soluble phosphorus and Citric acid phosphorus in compost products. With the increase of the initial carbon and phosphorus ratio, phoD gene and pqqC gene abundance (P < 0.05) were significantly up-regulated, thus increasing the secretion of phosphodiesterase and organic acid, improving the phosphorus availability in compost products. The potential host of phosphorus solubilizing genes was gradually transitioned from Proteobacteria to Firmicutes. The ppk gene and phosphorus accumulating bacteria abundance were significantly higher (CP20, CP25) at the later stage of composting (P < 0.05), indicating that the phosphorus accumulating potential of the bacterial community was more prominent in the low initial carbon and phosphorus ratio compost. This study elucidated the potential mechanism of action between functional genes and phosphorus availability, and demonstrated the feasibility of improving sludge phosphorus recovery efficiency by regulating the initial carbon and phosphorus ratio. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrogen source supply affects humifaction process of rice straw composting. • HS and HA concentrations at 50 d of composting is higher in R_CM than that in R_UR. • Functional bacteria have specificity under driven by different nitrogen source. • Protein-like nitrogen source alleviate competition within bacterial community. • Chicken manure supply stimulates collaborative division of bacterial community. This study investigated effects of high-nitrogen source (urea) (R_UR) and protein-like nitrogen source (chicken manure) (R_CM) on humification process during lignocellulose biomass composting. It demonstrated that decreasing ratio of crude fiber (CF), polysaccharide (PS) and amino acids (AAs) in R_CM (29.75%, 53.93% and 73.73%, respectively) was higher than that in R_UR (14.73%, 28.74% and 51.92%, respectively). Humic substance (HS) concentration increased by 7.51% and 73.05% during R_UR and R_CM composting, respectively. The lower total links, more independent modularization and higher proportion of positive correlations between functional bacteria and organic components was observed with R_CM network than R_UR, indicating that protein-like nitrogen source supply may alleviate competition within bacterial community. Moreover, chicken manure supply favorably selects greater special functional bacterial taxa (Pusillimonas, Pedomicrobium, Romboustia and other 24 genus) related to AAs and stimulates the collaborative division of bacterial community. This is significance for strengthening effective transformation of organic components. [ABSTRACT FROM AUTHOR]

• Malonic acid inhibits CO 2 release by affecting the tricarboxylic acid cycle. • MnO 2 acts through biological and non-biological pathways. • Malonic acid, MnO 2, malonic acid + MnO 2 can promote the formation of HA. • Malonic acid and MnO 2 can change bacterial community structure during composting. The aim of this study was to explore the effects of malonic acid (MA), manganese dioxide (MnO 2), malonic acid combined with manganese dioxide (MA + MnO 2) addition on reducing CO 2 emission and promoting humic substance (HS) formation during composting. The result showed that the addition of MA and MnO 2 were an efficient way to reduce CO 2 emission. Meanwhile, the CO 2 emissions in the MA + MnO 2 treatment was 36.8% less than that of the CK, and the amount of humic acid (HA) produced in the MnO 2 treatment was 38.7% higher than that of the CK. Structural equation models demonstrated that the addition of exogenous substance promoted the conversion of amino acids and reducing sugars to HA. The addition of exogenous substances was the main reason for influencing the concentration of HA. In general, this research provided theoretical supports for the addition of exogenous substances to promote HA formation during composting. [ABSTRACT FROM AUTHOR]

• Functional bacterial agents as core bacteria to produce lignocellulase. • Inoculation promoted the degradation of organic fractions. • Inoculation increased most core microbial metabolism. • The core bacteria and fungi of producing lignocellulase were identified. • The key factors of lignocellulosic degradation were identified by RDA and VPA. The aim of this paper was to identify the core microbes of producing lignocellulolytic enzymes during rice straw composting with functional bacterial agents inoculation. The results indicated that inoculation functional bacterial agents accelerated the degradation of organic matter and coarse fiber content by 7.58%, 8.82%, which were due to the fact that key enzymes and core microbes were stimulated. In addition, inoculation have reconstructed core microbes of producing lignocellulase. Meanwhile, inoculation functional bacterial agents not only as core bacteria to produce cellulase, xylanase and manganese peroxidase (MnP), but also increased most core microbial abundance. Redundancy analysis indicated that CMCase, xylanase, total nitrogen and MnP as key factors to affect the degradation of organic fractions in the core bacterial communities, while in the core fungal communities, were mainly affected by environmental factors (except for MnP). This study provided a theoretical basis for the efficiently degradation during agricultural wastes composting. [ABSTRACT FROM AUTHOR]

• Identified effects of ammonia-oxidizing bacteria (AOB) on humus formation. • AOB can increase humus production by releasing NH 3 emission. • AOB has also promoted nitrogen transformation. • AOB has dual functions to reduce nitrogen loss and improve compost quality. The aim of this study was to identify the effects of ammonia-oxidizing bacteria (AOB) inoculation on humus formation. Both nitrogen conversion and humus formation were considered as the main processes, because NH 4 +-N-like compounds not only substrates of nitrification, but also precursors of humus. During composting, the inoculation of AOB indeed increased humus concentration by fixing NH 3 emission as NH 4 +-N, but it has also promoted nitrogen transformation. While the main reason was the changed bacteria community structure caused by inoculating AOB. Moreover, the relationship between bacteria and nitrogen transformation and humus formation has become closer. And bacteria were more likely to synthesize humus. Therefore, it is conjectured that AOB inoculation could not only provide NH 4 +-N for humus formation, but also enhance the anabolism of microorganisms. This suppose has been confirmed by structural equation model in this study. Therefore, AOB inoculation has a driving effect on promoting humus formation. [ABSTRACT FROM AUTHOR]

• Fenton pretreatment promoted the organic fractions degradation. • Fenton pretreatment promoted the humic substances (HS) formation. • Bacterial communities structure and diversity were changed by Fenton pretreatment. • Key environmental factors and microbes were identified. The goal of this work was to explore the effect of Fenton pretreatment combined with bacteria inoculation on the formation of humic substances (HS) during rice straw composting. In this study, the compound bacterial agents were inoculated after Fenton pretreatment during rice straw composting. The results suggested that the coupling effects of Fenton pretreatment and bacteria inoculation promoted the humification process, which might be the reason of organic fractions degradation and transformation. In addition, the bacterial communities structure and diversity were changed by Fenton pretreatment and inoculation. Key microbial genera linking to the transformation of organic fractions were determined by network analysis. Redundancy analysis and structural equation model analysis indicated that Fenton pretreatment, inoculation, amino acid, soluble sugar and beta-diversity as the key factors affecting organic fractions transformation during composting. Therefore, the combined application Fenton pretreatment with bacteria inoculation provided a new method to promote the HS amount. [ABSTRACT FROM AUTHOR]

• LMW DOM was gradually transformed into HMW DOM during composting. • Core microorganisms associated with DOM transformation were identified. • Chemoheterotrophy was the major function of microorganisms during composting. • T, moisture and pH were key physicochemical factors affecting DOM stabilization. Transformation of DOM fractions with different molecular weights during composting of chicken manure (CM), garden waste (GW) and municipal solid waste (MSW) was evaluated in this study. The results revealed that DOM concentrations decreased by 49.8%, 53.9% and 86.4% during CM, GW and MSW composting, respectively. Meanwhile, low molecular weight (<650 Da) DOM was visibly transformed into high molecular weight (>10 kDa) DOM for enhancing their stability during composting. Core microorganisms promoting DOM stabilization were identified by network analysis, such as Prosthecobacter , Paenalcaligenes and Solibacillus. In addition, DOM composition was also related to the relative abundance of microbial metabolic function, such as chemoheterotrophy and aerobic chemoheterotrophy. Moreover, temperature, moisture and pH were identified as the key physicochemical factors affecting the DOM stabilization mediated by core microorganisms during composting. These above findings are helpful to regulate the DOM stabilization during composting and improve the quality of final composts. [ABSTRACT FROM AUTHOR]

• Biochar and montmorillonite addition reduced the bioavailability of Cu and Zn. • Biochar and montmorillonite addition changed the bacterial community structure. • Biochar significantly enhanced the correlation between bacteria and HM fractions. • Bacterial community was a key factor in reducing bioavailability of HM. The aim of this study was to explore the effects of adding biochar and montmorillonite alone on the correlations between bacteria and bioavailability of heavy metals (HM) during chicken manure composting. Three composting experiments were conducted, containing the without ameliorant, 10% biochar and 10% montmorillonite. The results showed that biochar and montmorillonite ameliorants significantly reduced the bioavailability of Cu by 90.3%, 81.2%, while that of Zn by 11.7%, 15.6%, respectively. Meanwhile, they also significantly changed bacterial community structure and enhanced the correlation between bacterial bands (i.e., 19, 24, 26 and 30) and HM fractions. This correlation was validated in network analysis. Structural equation models further confirmed that bacteria had a complete and effective pathway to influence the bioavailability of HM. In summary, this study suggested that biochar and montmorillonite additions were an effective regulation method to reduce the bioavailability of HM from composting system. [ABSTRACT FROM AUTHOR]

• Fenton pretreatment changed structure changes of the raw materials. • Part of lignocellulose-degrading enzymes were enhanced by Fenton pretreatment. • Key enzymes and environmental factors have been identified by RDA and SEMs. • Lignocellulose degradation efficiency was improved by Fenton pretreatment. This study aims to explore the effect of Fenton pretreatment on organic fractions, enzymes activities and microbial communities during composting. In this study, rice straw was chosen to be composted after pretreatment. The results indicated that Fenton pretreatment significantly increased the degradation of organic matter and coarse fiber contents, which might be the reason that Fenton pretreatment enhanced lignocellulose-degrading enzymes activities during composting, including CMCase, FPase, xylanase, manganese peroxidase, lignin peroxidase and laccase. Additionally, Fenton pretreatment reshaped bacteria community. The key enzymes and environmental factors, which affected organic fractions degradation were identified by redundancy analysis. Furthermore, structural equation modeling and variation partitioning analysis further revealed possible mechanisms of organic fractions degradation in different treatments during composting. In summary, the combined application Fenton pretreatment and composting improved lignocellulose degradation efficiency, which provided for an effective and environment-friendly way to manage lignocellulose wastes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Straw biochar addition effectively improved nitrogen fixation during composting. • Inhibiting denitrification and NH 4 +-N transformation were the main means. • Biochar addition reduced microbial numbers involved in nitrogen transformation. • The microbial conversion of NO 3 –-N and organic nitrogen were strengthened. • The effect of biochar derived from maize straw was better than that of rice straw. 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 NH 4 +-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 NO 3 –-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. [ABSTRACT FROM AUTHOR]

• Fenton-like reactions increased the production of lignocellulolytic enzymes. • Fenton-like reactions promoted the degradation of lignocellulose. • Fenton-like reactions changed fungal communities composition and diversity. • Functional modular microbes and key species in different treatments were identified. • Reducing sugars, organic matter and amino acids were key microhabitat factors of functional modular microbes. This study aimed to explore the effect of Fenton-like reactions on lignocellulosic degradation performance and identify their driving factors during composting. Rice straw was pretreated by inoculating Aspergillus fumigatus Z1 and then adding Fe (II), which resulted in Fenton-like reactions. The treatment groups included CK (control), Fe (addition of Fe (II)), Z1 (inoculation of A. fumigatus Z1), and Fe + Z1 (inoculation of A. fumigatus Z1 and addition of Fe (II)). The results suggested that Fenton-like reactions can produce lignocellulolytic enzymes and degrade lignocellulose, due to the variation in microbial community composition and diversity. In addition, functional modular microbes were identified by network analysis, which can produce endoglucanase and xylanase. Regarding ligninase, bacteria were more favorable for producing manganese peroxidase, and fungi were more favorable for producing laccase. Additionally, reducing sugars, organic matter, total nitrogen and amino acids were key microhabitat factors of functional modular bacteria, while organic matter, reducing sugars, amino acids and C/N were key microhabitat factors of functional modular fungi, thereby promoting the degradation of lignocellulose. This study provides technical support for lignocellulosic degradation based on Fenton-like reactions. [ABSTRACT FROM AUTHOR]

Composting is an efficient way of recycling wastes, serious mineralization will lead to loss of organic carbon components in the biodegradation process, which will affect the quality of composting products. Calcination technology was adopted to improve the ability of clay minerals to adsorb and retain organic carbon components, and was applied to chicken manure composting. Five treatments (control group (CK), calcined montmorillonite (M-), montmorillonite (M), calcined illite (I-) and illite (I)) were executed. The results indicated that calcined clay minerals significantly reduced organic carbon loss (CK: 57.22%, M-: 54.56%, M: 56.86%, I-: 52.39% and I: 56.08%) and most of them in the form of humic acids. Therefore, the properties of carbon components were more stable, and ultimately improved quality of final compost products. Meanwhile, the network complexity, interactions and contribution of core bacteria involved in the formation of organic carbon were enhanced in the calcined clay minerals treatments through microbial analysis. Moreover, a series of statistical informatics analysis verified that specific structure of calcined clay minerals could indeed retain organic carbon by enhancing role of core bacteria and physicochemical factors. Therefore, this article revealed mechanism of calcined clay minerals retained organic carbon and proposed rational recommendations for practice of composting. [Display omitted] [ABSTRACT FROM AUTHOR]