Protein and carbohydrate drive microbial responses in diverse ways during different animal manures composting

Innovative insights into organic nitrogen degradation through protein family domains analysis in chicken and pig manure composting using metagenomic sequencing

The nitrogen loss in composting is primarily driven by the transformation of organic nitrogen, yet the mechanisms underlying the degradation process remain incompletely understood. This study employed protein family domains (Pfams) analysis based on metagenomic sequencing to investigate the functional characteristics, key microorganisms, and environmental parameters influencing organic nitrogen degradation in chicken manure and pig manure composting. 154 Pfams associated with ammonification function were identified. Predominant Pfams: proteolytic peptidase, followed by chitin/cell wall degraders, least involved in nucleic acid degradation. Ammonifying microbial diversity was basically consistent among compost types, particularly in the thermophilic stage with the peak of abundance of dominant ammonifying microorganisms. Viruses played an important role in ammonification process, especially Uroviricota. 26 key ammonifying genera were identified by the microbial network. pH dominated the metabolic activity of ammonifying microorganisms in various manure compost types, primarily consisting of protein-degrading bacteria with stable community structures.

Pilot-scale membrane-covered composting of food waste: Initial moisture, mature compost addition, aeration time and rate

The impact of different operational parameters on the composting efficiency and compost quality during pilot-scale membrane-covered composting (MCC) of food waste (FW) was evaluated. Four factors were assessed in an orthogonal experiment at three different levels: initial mixture moisture (IMM, 55 %, 60 %, and 65 %), aeration time (AT, 6, 9, and 12 h/d), aeration rate (AR, 0.2, 0.4, and 0.6 m3/h) and mature compost addition ratio (MC, 2 %, 4 %, and 6 %). Results indicated that 55 % IMM, 6 h/d AT, 0.4 m3/h AR, and 4 % MC addition ratio simultaneously provided the compost with the maximum cumulative temperature and the minimum moisture. It was shown that the IMM was the driving factor of this optimum composting process. On contrary, the optimal parameters for reducing carbon and nitrogen loss were 65 % IMM, 6 h/d AT, 0.4 m3/h AR, and 2 % MC addition ratio. The AR had the most influence on reducing carbon and nitrogen losses compared to all other factors. The optimal conditions for compost maturity were 55 % IMM, 9 h/d AT, 0.2 m3/h AR, and 6 % MC addition ratio. The primary element influencing the pH and electrical conductivity values was the AR, while the germination index was influenced by IMM. Protein was the main organic matter limiting the composting efficiency. The results of this study will provide guidance for the promotion and application of food waste MCC technology, and contribute to a better understanding of the mechanisms involved in MCC for organic solid waste treatment.

Effects of initial corncob particle size on the short-term composting for preparation of cultivation substrates for Pleurotus ostreatus

The short-term composting based on corncob for preparing Pleurotus ostreatus cultivation medium originated from agricultural production practices and so lacked systematic investigation. In this study, the influences of a Dafen (15 mm, DFT) and Xiaofen (5 mm, XFT) initial particle size (IPS) of corncob on the microbial succession and compost quality were examined. Results demonstrated that XFT compost was better suited for mushroom cultivation due to its high biological efficiency of 70 % and the absence of contamination. The composting microbes differed significantly between the DFT and XFT composts. During composting, the genera of Bacillus, Acinetobacter, Lactobacillus, Streptomyces, and Paenibacillus were majorly found in the DFT compost, while Acinetobacter, Lactobacillus, Puccinia, Bacteroides, and Bacillus genera dominated the XFT compost. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that throughout the thermophilic phase, XFT compost had much greater relative abundances of sequences relevant to energy, carbohydrate, and amino acid metabolism than DFT compost. Analysis of network correlations and Mantel tests indicated that IPS reduction could increase microbial interactions. Overall, adjusting the IPS of corncob to 5 mm increased microbial interactions, improved compost quality, and thereby boosted the P. ostreatus yield. These findings will be pertinent in optimizing the composting process of cultivation medium for P. ostreatus.

Machine-learning intervention progress in the field of organic waste composting: Simulation, prediction, optimization, and challenges

Aerobic composting stands as a widely-adopted method for treating organic solid waste (OSW), simultaneously producing organic fertilizers and soil amendments. This biologically-driven biochemical reaction process, however, presents challenges due to its complex non-linear metabolism and the heterogeneous nature of the solid medium. These characteristics inherently limit the simulation accuracy and efficiency optimization in aerobic composting. Recently, significant efforts have been made to simulate and control composting process parameters, as well as predicting and optimizing composting product quality. Notably, the integration of machine learning (ML) in aerobic composting of organic waste has garnered considerable attention for its applicability and predictive capability in exploring the complex non-linear relationships of organic waste composting parameters. Despite numerous studies on ML applications in OSW composting, a systematic review of research findings in this field is lacking. This study offers a systematic overview of the application level, current status, and versatility of ML in OSW composting. It spans various aspects, such as compost maturity, environmental pollutants, nutrients, moisture, heat loss, and microbial metabolism. The survey reveals that ML-intervention predominantly focuses on compost maturity and environmental pollutants, followed by nutrients, moisture, heat loss, and microbial activity. The most commonly employed predictive models and optimization algorithms are artificial neural networks (47%) and genetic algorithms (10%). These demonstrate high prediction accuracy and maximize composting efficiency in the simulation and prediction of organic waste composting, alongside regulation of key parameters. Deep neural networks and ensemble learning models prove effective in achieving superior predictive performance by selecting feature variables in compost maturity and pollutant residue prediction of organic waste composting in a simpler and more objective manner.

Investigating fungal community characteristics in co-composted cotton stalk and various livestock manure products

Agricultural wastes, comprising cotton straw and livestock manure, can be effectively managed through aerobic co-composting. Nevertheless, the quality and microbial characteristics of co-composting products from different sources remain unclear. Therefore, this study utilized livestock manure from various sources in Xinjiang, China, including herbivorous sheep manure (G), omnivorous pigeon manure (Y), and pigeon-sheep mixture (GY) alongside cotton stalks, for a 40-day co-composting process. We monitored physicochemical changes, assessed compost characteristics, and investigated fungal community. The results indicate that all three composts met established composting criteria, with compost G exhibiting the fastest microbial growth and achieving the highest quality. Ascomycota emerged as the predominant taxon in three compost products. Remarkably, at the genus level, the biomarker species for G, Y, and GY are Petromyces and Cordyceps, Neurospora, and Neosartorya, respectively. Microorganisms play a pivotal role in organic matter degradation, impacting nutrient composition, demonstrating significant potential for the decomposition and transformation of compost components. Redundancy analysis indicates that potassium, total organic carbon, and C:N are key factors influencing fungal communities. This study elucidates organic matter degradation in co-composting straw and livestock manure diverse sources, optimizing treatment for efficient agricultural waste utilization and sustainable practices.

Co-composting sugar-containing waste with chicken manure-A new approach to carbon sequestration

Improving resource use is a pressing research issue because of the huge potential organic waste market. Composting is a recycling technique, treatment to achieve the dual effect of resource recovery and zero waste. Waste composition varies: for example, chicken manure is rich in protein, straw contains wood fibres, fruit and vegetables contain sugar, and food waste contains starch. When considering combining waste streams for composting, it is important to ask if this approach can reduce overall composting costs while achieving a more concentrated result. Chicken manure, in particular, presents a unique challenge. This is due to its high protein content. The lack of precursor sugars for glucosamine condensation in chicken manure results in lower humus content in the final compost than other composting methods. To address this, we conducted experiments to investigate whether adding sugary fruits and vegetables to a chicken manure composting system would improve compost quality. To improve experimental results, we used sucrose and maltose instead of fruit and vegetable waste. Sugars added to chicken manure composting resulted in a significant increase in humic substance (HS) content, with improvements of 9.0% and 17.4%, respectively, compared to the control. Sucrose and maltose have a similar effect on the formation of humic substances. These results demonstrate the feasibility of composting fruit and vegetable waste with chicken manure, providing a theoretical basis for future composting experiments.

Responses of greenhouse gas emissions to aeration coupled with functional membrane during industrial-scale composting of dairy manure: Insights into bacterial community composition and function

Greenhouse gas (GHG) emissions from manure management processes deserve more attention. Using three industrial-scale experiments, this study comprehensively evaluated the effects of different aeration coupled with semi-permeable membrane-covered strategies on the structure and function of bacterial communities and their impact on GHG emissions during dairy manure aerobic composting. The succession of the bacterial communities tended to be consistent for similar aeration strategies. Ruminiclostridium and norank_f__MBA03 were significantly positively correlated with the methane emission rate, and forced aeration coupled with semi-permeable membrane-covered decreased GHG emissions by inhibiting these taxa. Metabolism was the most active function of the bacterial communities, and its relative abundance accounted for 75.69%-80.23%. The combined process also enhanced carbohydrate metabolism and amino acid metabolism. Therefore, forced aeration coupled with semi-permeable membrane-covered represented a novel strategy for reducing global warming potential by regulating the structure and function of the bacterial communities during aerobic composting of dairy manure.

Bacillus licheniformis inoculation promoted humification process for kitchen waste composting: Organic components transformation and bacterial metabolic mechanism

Kitchen waste (KW) composting always has trouble with slow humification process and low humification degree. The objective of this study was to develop potentially efficient solutions to improve the humification of KW composting, accelerate the humus synthesis and produce HS with a high polymerization degree. The impact of Bacillus licheniformis inoculation on the transformation of organic components, humus synthesis, and bacterial metabolic pathways in kitchen waste composting, was investigated. Results revealed that microbial inoculation promoted the degradation of organic constituents, especially readily degradable carbohydrates during the heating phase and lignocellulose fractions during the cooling phase. Inoculation facilitated the production and conversion of polyphenol, reducing sugar, and amino acids, leading to an increase of 20% in the content of humic acid compared to the control. High-throughput sequencing and network analysis indicated inoculation enriched the presence of Bacillus, Lactobacillus, and Streptomyces during the heating phase, while suppressing the abundance of Pseudomonas and Oceanobacillus, enhancing positive microbial interactions. PICRUSt2 analysis suggested inoculation enhanced the metabolism of carbohydrates and amino acids, promoting the polyphenol humification pathway and facilitating the formation of humus. These findings provide insights for optimizing the humification process of kitchen waste composting by microbial inoculation.

In Situ Toxicity Reduction and Food Safety Assessment of Pak Choi (Brassica campestris L.) in Cadmium-Contaminated Soil by Jointly Using Alkaline Passivators and Organic Fertilizer

An economical and effective method is still lacking for cadmium (Cd) toxicity reduction and food product safety improvement in soil-vegetable systems. Therefore, this study aimed to reduce the Cd toxicity to pak choi (Brassica campestris L.) by jointly using passivators and organic fertilizer, highlighting food products' safety based on pot experiments. The results showed that compared with the control, organic fertilizer decreased the Cd content in edible parts and the soil's available Cd by 48.4% and 20.9% on average, respectively, due to the 0.15-unit increases in soil pH. Once jointly applied with passivators, the decrements increased by 52.3-72.6% and 32.5-52.6% for the Cd content in edible parts and for the soil's available Cd, respectively, while the pH increment increased by 0.15-0.46 units. Compared with the control, the transport factor of Cd was reduced by 61.9% and 50.9-55.0% when applying organic fertilizer alone and together with the passivators, respectively. The combination treatment of biochar and organic fertilizer performed the best in decreasing the Cd content in the edible parts and the soil's available Cd. The combination treatment of fish bone meal and organic fertilizer induced the greatest increases in soil pH. The grey relational analysis results showed that the combination treatment of biochar and organic fertilizer performed the best in reducing the potential Cd pollution risk, thereby highlighting the vegetable food safety. This study provides a potential economical and effective technology for toxicity reduction and food safety in Cd-polluted soil.

Moderately delayed maturation of composting promotes the reduction of guild-plant pathogenic fungi within vegetable waste

The relationships among the relative abundance of guild-plant pathogenic fungi, compost maturation index, and microbial community variation during vegetable waste composting, which are influenced by the C/N ratio, remain poorly understood. To address this, fungal communities were analyzed in composting treatments with C/N ratios of approximately 15 (CN15) and 25 (CN25), using vegetable waste as the primary raw material. The CN15 treatment showed greater microbial community variation and a better overall compost maturation index value than the CN25 treatment. However, the CN25 treatment had a greater decline in plant-pathogenic fungi than the CN15 treatment. Notably, the relative abundance of guild-plant pathogenic fungi was significantly negatively related to the compost maturity index in the CN25 treatment, while no significant relationship was observed in the CN15 treatment. This study suggests that the moderately delayed maturation of composting is beneficial for reducing guild-plant pathogenic fungi in vegetable waste.

Comparison of bacterial and fungal communities structure and dynamics during chicken manure and pig manure composting

Composting is a sustainable and eco-friendly technology that turns animal waste into organic fertilizers. It remains unclear whether differences exist in the structure of microbial communities during different livestock manure composting. This study analyzed the dynamic change of bacterial and fungal communities, metabolic function, and trophic mode during chicken manure (CM) and pig manure (PM) composting based on 16S rRNA and ITS sequencing. Environmental factors were investigated for their impact on microbial communities. During composting, bacterial diversity decreased and then increased, while fungal diversity slightly increased and then decreased. Saccharomonospora and Aspergillus were the dominant genera and key microorganisms in CM and PM, respectively, which played crucial roles in sustaining the stability of the ecological network structure in the microbial ecology and participating in metabolism. Saccharomonospora gradually increased, while Aspergillus increased at first and then decreased. PM had better microbial community stability and more keystone taxa than CM. In CM and PM, the primary function of bacterial communities was metabolism, while saprotroph was the primary trophic mode of fungal communities. Dissolved organic carbon (DOC) was the primary factor influencing the structure and function of microbial communities in CM and PM. In addition to DOC, pH and moisture were important factors affecting the fungal communities in CM and PM, respectively. These results show that the succession of bacteria and fungi in CM and PM proceeded in a similar pattern, but there are still some differences in the dominant genus and their responses to environmental factors.

Risk assessment and dissemination mechanism of antibiotic resistance genes in compost

In recent years, the excessive of antibiotics in livestock and poultry husbandry, stemming from extensive industry experience, has resulted in the accumulation of residual antibiotics and antibiotic resistance genes (ARGs) in livestock manure. Composting, as a crucial approach for the utilization of manure resources, has the potential to reduce the levels of antibiotics and ARGs in manure, although complete elimination is challenging. Previous studies have primarily focused on the diversity and abundance of ARGs in compost or have solely examined the correlation between ARGs and their carriers, potentially leading to a misjudgment of the actual risk associated with ARGs in compost. To address this gap, this study investigated the transfer potential of ARGs in compost and their co-occurrence with opportunistic pathogenic bacteria by extensively analyzing metagenomic sequencing data of compost worldwide. The results demonstrated that the potential risk of ARGs in compost was significantly lower than in manure, suggesting that composting effectively reduces the risk of ARGs. Further analysis showed that the microbes shifted their life history strategy in manure and compost due to antibiotic pressure and formed metabolic interactions dominated by antibiotic-resistant microbes, increasing ARG dissemination frequency. Therefore, husbandry practice without antibiotic addition was recommended to control ARG evolution, dissemination, and abatement both at the source and throughout processing.

Amended compost alleviated the stress of heavy metals to pakchoi plants and affected the distribution of heavy metals in soil-plant system

With the development of the social economy, soil heavy metal pollution has become a common worldwide issue. Therefore, the remediation of soil heavy metal pollution is imminent. This study aimed to investigate the effect of amended compost on reducing heavy metal bioavailability in soil and relieving heavy metals stress on plants under Cu and Zn stress in a pot experiment. To model the restoration of heavy metal-polluted farming soil, conventional compost (CKw), activated carbon compost (ACw), modified biochar compost (BCw) and rhamnolipid compost (RLw) were utilized. The results showed that the application of amended compost could promote the growth and quality of pakchoi and enhance the stress ability of malondialdehyde and antioxidant enzymes to heavy metals. The distribution of Cu and Zn in different subcellular parts of pakchoi was also affected. The application of amended compost significantly reduced the heavy metals content in the shoot of pakchoi, among which the content of Cu and Zn in the shoot of pakchoi in RLw was significantly decreased by 57.29% and 60.07%, respectively. Our results can provide a new understanding for efficient remediation of contaminated farmland soil by multiple heavy metals.

Effects of micro-positive pressure environment on nitrogen conservation and humification enhancement during functional membrane-covered aerobic composting

Aerobic composting is a humification process accompanied by nitrogen loss. This study is the first research systematically investigating and elucidating the mechanism by which functional membrane-covered aerobic composting (FMCAC) reduces nitrogen loss and enhances humification. The variations in bioavailable organic nitrogen (BON) and humic substances (HSs) in different composting systems were quantitatively studied, and the functional succession patterns of fungal groups were determined by high-throughput sequencing and FUNGuild. The FMCAC improved oxygen utilization and pile temperature, increased BON by 29.95 %, reduced nitrogen loss by 34.00 %, and enhanced humification by 26.09 %. Meanwhile, the FMCAC increased the competitive advantage of undefined saprotroph and significantly reduced potential pathogenic fungi (<0.10 %). Structural equation modeling indicated that undefined saprotroph facilitated the humification process by increasing the production of BON and storing BON in stable humic acid. Overall, the FMCAC increased the safety, stability, and quality of the final compost product.

Revisiting the oldest manure of India, Kunapajala: Assessment of its animal waste recycling potential as a source of plant biostimulant

India's oldest documented manure, most commonly referred to as Kunapajala, has a long history of over 1,000 years in crop cultivation. Kunapajala is primarily an in-situ decomposition technology of animal waste and can potentially provide an eco-friendly pipeline for recycling bio-waste into essential plant nutrients. This traditional animal manure, in addition, also contains dairy excreta (e.g., feces and urine), dairy products (e.g., milk and ghee), natural resources (e.g., honey), broken seeds or grains, and their non-edible by-product waste. Here, we aimed to assess the waste recycling and plant biostimulant potential of Kunapajala prepared from livestock (e.g., Black Bengal goats) or fish (e.g., Bombay duck) post-processed wastes over different decomposition periods, e.g., (0, 30, 60, and 90-days). In this study, an in-situ quantification of livestock- (lKPJ) and fish-based Kunapajala (fKPJ) reveals a dynamic landscape of essential plant primary nutrients, e.g., (0.70 &gt; NH4-N &lt; 3.40 g•L−1), (100.00 &gt; P2O5 &lt; 620.00 mg•L−1), and (175.00 &gt; K2O &lt; 340.00 mg•L−1), including other physico-chemical attributes of Kunapajala. Using correlation statistics, we find that the plant-available nutrient content of Kunapajala depicts a significant (p &lt; 0.0001) transformation over decomposition along with microbial dynamics, abundance, and diversities, delineating a microbial interface to animal waste decomposition and plant growth promotion. Importantly, this study also reports the indole 3-acetic acid (IAA) content (40.00 &gt; IAA &lt; 135.00 mg•L−1) in Kunapajala. Furthermore, the bacterial screening based on plant growth-promoting traits and their functional analyses elucidate the mechanism of the plant biostimulant potential of Kunapajala. This assay finally reports two best-performing plant growth-promoting bacteria (e.g., Pseudomonas chlororaphis and Bacillus subtilis) by the 16S ribotyping method. In support, in-planta experiments have demonstrated, in detail, the bio-stimulative effects of Kunapajala, including these two bacterial isolates alone or in combination, on seed germination, root-shoot length, and other important agronomic, physio-biochemical traits in rice. Together, our findings establish that Kunapajala can be recommended as a source of plant biostimulant to improve crop quality traits in rice. Overall, this work highlights Kunapajala, for the first time, as a promising low-cost microbial technology that can serve a dual function of animal waste recycling and plant nutrient recovery to promote sustainable intensification in agroecosystems.

Phytotoxicity of farm livestock manures in facultative heap composting using the seed germination index as indicator

Static facultative heap composting of animal manure is widely used in China, but there is almost no systematic research on the phytotoxicity of the produced compost. Here, we evaluated the phytotoxic variation in compost produced by facultative heap composting of four types of animal manure (chicken manure, pig manure, sheep manure, and cattle manure) using different plant seeds (cucumber, radish, Chinese cabbage, and oilseed rape) to determine germination index (GI). The key factors that affected GI values were identified, including the dynamics of the phytotoxicity and microbial community during heap composting. Sensitivity to toxicity differed depending on the type of plant seed used. Phytotoxicity during facultative heap composting, evaluated by the GI, was in the order: chicken manure (0-6.6 %) < pig manure (14.4-90.5 %) < sheep manure (46.0-93.0 %) < cattle manure (50.2-105.8 %). Network analysis showed that the volatile fatty acid (VFA) concentration was positively correlated with Firmicutes abundance, and NH₄⁺-N was correlated with Actinobacteria, Proteobacteria, and Bacteroidetes. More bacteria were stimulated to participate in conversions of dissolved organic carbon, dissolved nitrogen, VFA, and ammonia-nitrogen (NH₄⁺-N) in sheep manure heap composting than that in other manure. The GI was most affected by VFA in chicken manure and cattle manure heap composting, while NH₄⁺-N was the main factor affecting the GI in pig manure and sheep manure compost. The dissolved carbon and nitrogen content and composition, as well as the core and proprietary microbial communities, were the primary factors that affected the succession of phytotoxic substances in facultative heap composting, which in turn affected GI values. In this study, the key pathways of livestock manure composting that affected GI and phytotoxicity were found and evaluated, which provided new insights and theoretical support for the safe use of organic fertilizer.

Metagenomic analysis reveals the microbial degradation mechanism during kitchen waste biodrying

Biodrying is a treatment to remove moisture using bio-heat generated during organic degradation. Organic matter degradation and microbial metabolism were studied during the whole kitchen waste biodrying, using metagenomic analysis. After the 25-day biodrying process, carbohydrate, protein and lipid contents decreased by 83.7%, 27.8% and 79.3%, respectively, and their degradation efficiencies increased after the thermophilic phase. Lipase activity exceeded 10 mmol d^-1 g^-1 throughout biodrying. Cellulase and lipase activities recovered by 2.21% and 5.77%, respectively, after the thermophilic phase, while the protease activity had a maximum increment of 347%. Metabolic analysis revealed that carbohydrate, amino acid and lipid metabolism was possibly inhibited by the high temperature, but the relative abundances of related predicted functions recovered by more than 0.9%, 7% and 11%, respectively, by the end of biodrying. Protein function prediction suggests that β-oxidation, fatty acid biosynthesis, and the degradation of cellulose and chitin were possibly enhanced during the thermophilic phase. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that leucine, isoleucine and lysine could ultimately degraded to acetyl-CoA. Weissella, Aeribacillus and Bacillus were the genera with the most enriched functional genes during the whole biodrying process. These findings help elucidate the microbial degradation processes during biodrying, which provides further scientific support for improving the application of biodrying products.

Di-n-butyl phthalate negatively affects humic acid conversion and microbial enzymatic dynamics during composting

To understand the effects of phthalic acid esters (PAEs) on humic acid (HA) conversion, enzymatic and specific metabolic dynamics during composting under di-n-butyl phthalate (DBP) stress were evaluated for the first time. The results indicated that HA conversion was mainly related to bacteria rather than fungi, with positive associations with Actinobacteria, Chloroflexi, and Gemmatimonadota (all P < 0.05), and negative associations with Proteobacteria and Bacteroidota (all P < 0.05), while DBP stress retarded HA formation by altering the core microbes related to HA formation and their metabolic functions. Moreover, typical hydrolase and oxidoreductase activities were altered under DBP stress, proteases and cellulases were hindered, and peroxidases as well as polyphenol oxidases were promoted during composting. Overall, our data shows that DBP stress can retard HA formation and compost maturation by interfering with microbial activity. This study provides potentially useful information for the degradation and reuse of PAE-contaminated waste.

Succession of the Bacterial Communities and Functional Characteristics in Sheep Manure Composting

Bacterial community is a key factor affecting aerobic composting, and understanding bacterial community succession is important to revealing the mechanism of organic matter degradation. In this study, the succession and metabolic characteristics of bacterial communities were explored in 45 days composting of sheep manure and wheat straw by using high-throughput sequencing technology and bioinformatics tools, respectively. Results showed that the alpha diversity of bacterial community significantly decreased in the thermophilic (T2) phase and then recovered gradually in the bio-oxidative (T3) and the maturation (T4) phases. Bacterial communities varied at different stages, but there were 158 genera in common bacterial species. Unclassified_f_Bacillaceae, Oceanobacillus, Bacillus, Pseudogracilibacillus, and Nocardiopsis were identified as keystone bacterial genera. Eleven genera were significantly correlated (p < 0.05), or even extremely significantly correlated (p < 0.001), with the physicochemical factors. Redundancy analysis (RDA) showed that changes of bacterial community diversity correlated with physicochemical factors. The highest relative abundances were amino acid and carbohydrate metabolism among the metabolic groups in the compost. These results will provide theoretical support for further optimizing sheep manure composting conditions and improving the quality of organic fertilizers.

Linking Microbial Community Succession With Substance Transformation in a Thermophilic Ectopic Fermentation System

Ectopic fermentation system (EFS) is an effective technology for treating mass livestock manure. However, the associations between microbial communities and substance transformation remain controversial. This study aimed to investigate chicken manure EFS lasting 170 days using 16S rRNA sequencing and electrochemical, spectroscopic, and chromatographic analyses. The results showed a noticeable transformation of protein-like substances into humus-like substances. Meanwhile, the electron–accepting capacity increased persistently, effectively reflecting the humification of organic substances. The contents of phenols that promoted electron transfer continued to increase from 2.80 to 6.00%, which could be used as a maturity indicator for EFS. During the heating period, the dominant microbial communities were Chloroflexi and Proteobacteria, whereas thermotolerant bacteria Cyanobacteria and Planctomycetes were significantly enriched from 1.64 to 50.15% during the continuous thermophilic period of EFS. The correlation analysis manifested that these thermotolerant bacteria were the major functional bacteria for the formation of phenols and the key to driving the humification of organic substances. This study provides insights into understanding the humification mechanisms and implementing regulatory strategies in EFS.

Ventilation induced evolution pattern of archaea, fungi, bacteria and their potential roles during co-bioevaporation treatment of concentrated landfill leachate and food waste

To obtain a favorable aeration type in co-bioevaporation treatment of concentrated landfill leachate and food waste, and to deeply understand the co-bioevaporation mechanisms, the temporal evolution differences of archaea, fungi and bacteria as well as the related microbial metabolism genes and functional enzymes under intermittent ventilation (IV) and continuous ventilation (CV) were investigated. Results through metagenomics analysis showed that the less sufficient oxygen and longer thermophilic phase in IV stimulated the vigorous growth of archaea, while CV was beneficial for fungal growth. Even genes of carbohydrates and lipids metabolism and ATP-associated enzymes (enzyme 2.7.13.3 and 3.6.4.12), as well as peptidoglycan biosynthesis enzyme (enzyme 3.4.16.4), were more abundant in CV, IV hold better DNA repair ability, higher microbial viability, and less dehydrogenase sensitivity to temperatures due to the critical contribution of Pseudomonas (3.1-45.9%). Furthermore, IV consumed a similar amount of heat for water evaporation with nearly half of the ventilation of CV and was a favorable aeration type in the practical application of co-bioevaporation.

Key factors affecting seed germination in phytotoxicity tests during sheep manure composting with carbon additives

The germination index (GI) was widely applied to evaluate the phytotoxicity of compost. This study investigated the key phytotoxicity factors affecting seed germination in compost by using aqueous extracts in seed germination tests. The relationship between water-soluble substances in compost and seed germination, and their association with the microbial community were identified. In this study, sheep manure (SM) composted along or with three carbon additives (mushroom substrate, MS; cornstalks, CS; garden substrate, GS) for 49 days and, during this time, changes in multiple physical-chemical parameters, carbon and nitrogen matters, germination indexes (GI) and the compost microbiome were monitored. The results showed that all additives decreased water-soluble total nitrogen (TN), ammonium nitrogen (NH₄⁺-N) and low molecular weight organic acids, and significantly improved the seed germination indexes (seed germination rate, radical length and GI). The GI was correlated with water-soluble carbon degradation products (TOC, butyric acid, humic acid) and certain bacteria (Planifilum, Oceanobacillus, Ruminococcaceae_UCG_005 and Saccharomonospora). A structural equation model revealed that the main factors affecting seed germination were TOC (SM compost), acetic acid (SM+MS compost), humic acid (SM+CS compost), and pH (SM+GS compost). Low TOC and low molecular weight organic acids contents and higher humic acid content promoted GI. The research results could provide theoretical basis and measures for directional regulation of compost maturity.

Revealing the link between evolution of electron transfer capacity of humic acid and key enzyme activities during anaerobic digestion

Humic acid (HA) is an important active compound formed during anaerobic digestion process, with a complex structure and dynamic electron transfer capacity (ETC). However, the mechanisms by which these macromolecular organic compounds dynamically interact with the microbial anaerobic digestion process at different operating temperatures are still unclear. In this study, the link between the evolution of the ETC of HAs and the microbial community under mesophilic and thermophilic conditions was investigated. The results showed an increasing trend in the ETC of HAs in both mesophilic (671-1479 μmol gHA^-1) and thermophilic (774-1506 μmol gHA^-1) anaerobic digestion (AD) until day 25. The ETC was positively correlated with the bacterial community of hydrolytic and acidogenic phases, but negatively correlated with the archaeal community of the methanogenic phase. Furthermore, the relationship between ETC and key enzyme activity was explored using a co-occurrence network analysis. HAs revealed a high potential to promote key enzyme activities during hydrolysis (amylase and protease) and acidification (acetate kinase, butyrate kinase, and phosphotransacetylase) while inhibiting the key enzyme activity in the methanogenic phase during the anaerobic digestion process. Moreover, HAs formed under thermophilic conditions had a greater influence on key enzyme activities than those formed under mesophilic conditions. This study advances our understanding of the mechanisms underlying the influence of HAs on anaerobic digestion performance.

Fate of antibiotic resistance genes in industrial-scale rapid composting of pharmaceutical fermentation residue: The role implications of microbial community structure and mobile genetic elements

Composting is an effective technology to recycle organic solid waste as a green resource. However, pharmaceutical fermentation residue (PFR) contains a variety of pollutants, such as residual drug and antibiotic resistance genes (ARGs), which limits the green cycle of using PFR as a resource. To promote the green recycling of PFR, this study evaluated the characteristics of abundance and the response relationship of ARGs during the process of rapid composting. Different rapid composting samples were collected, and DNA was extracted from each sample. The absolute abundance of ARGs was quantified using quantitative PCR, and the microbial community structure was identified using high-throughput sequencing. The results showed that ermB, ermF, tetM and tetQ were reduced by 89.55%, 15.10%, 89.55%, and 82.30% respectively, and only sul2 increased by approximately 5-fold. Mobile genetic elements (MGEs) directly affected the changes in abundance of ARGs. As typical MGEs, intl1 and intl2 decreased by 3.40% and 54.32%, respectively. Potential host microorganisms important factors that affected ARGs and MGEs. A network analysis indicated that the potential host microorganisms were primarily distributed in Firmicutes and Proteobacteria at the phylum level. The pH and content of water-extractable sulfur were physicochemical parameters that substantially affected the abundance of potential host microorganisms through redundancy analysis. Industrial-scale rapid composting could reduce the number of ARGs and shorten the composting cycle, which merits its popularization and application.

Two types nitrogen source supply adjusted interaction patterns of bacterial community to affect humifaction process of rice straw composting

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.

Community-level dormancy potential regulates bacterial beta-diversity succession during the co-composting of manure and crop residues

This study aimed to disclose the bacterial diversity succession during the co-composting of manure and crop residues and to provide new insight into the role of community-level dormancy potential in diversity succession. Illumina sequencing and PICRUSt-estimated metagenomes were used for this purpose. The bacterial richness and phylogenetic diversity decreased in the early and middle stages of composting and were maintained to a stable status in the late stage. Both composting phases and raw materials impacted the aforementioned alpha diversity significantly, while the composting phases had a greater (80%-94%) impact than the raw materials (1%-18%). Bacterial beta-diversity succession exhibited selectivity as the composting proceeded, and the dominant taxa changed into salt- and heat-resistant genera such as Bacillus, Glycomyces, and Halocella. Meanwhile, Georgenia, Actinomadura, and Ruminofilibacter were identified as the dominant predictor taxa of bacterial community succession in composting. Roughly, the abundance of genes underlying dormancy strategies, including sporulation factors (spo0A gene), toxin-antitoxin systems (dinJ/yafP, mazF/E, hipA/O, and relA/E genes), and resuscitation-promoting factors (rpfC gene), increased as composting proceeded and reached the highest in the thermophilic or maturation phases. Co-occurring relationships between bacterial communities and genes underlying dormancy strategies in different composting phases comprised multiple associations dominated by positive edges (50%-97%). The stability in genes underlying dormancy strategies and aggregate dormancy potential had a positive linear correlation with that in bacterial beta diversity (R² = 0.26-0.42; P < 0.05), but not related significantly to that in richness and phylogenetic diversity. This study highlighted the importance of understanding how community-level dormancy strategies mediated microbial succession in composting to better predict compost maturity and product quality.

The key bacteria as the "Activator" promotes the rapid degradation of organic compounds during the start-up of low-temperature compost

During composting of chicken manure, the degradation of organic compounds is a key factor affecting the fate of chicken manure in the low temperature environment. Here, we studied the changes of main organic compounds, including carbohydrates, proteins and lipids and the role of key bacteria in composted at 10 °C. The degradation rates of total sugar and protein in inoculation group were 41.11% and 47.63% respectively, which were related to the activities of carbohydrate related enzymes. The key bacteria from composting have better degradation of organic compounds capacities than others, and improve the enzyme activity. Cluster heatmap verified that the microbial community and enzyme activity were the primary driving factors of organic compounds degradation. Thus, the co-regulation of key microbial and enzyme activity made it possible to promote degradation of organic compounds drastically by microbial metabolism. These above findings are beneficial to improving the utilization of livestock manure in cold areas.

Evaluation of nitrogen conversion pathway during composting under amoxicillin stress: Mainly driven by core microbial community

The aim of this study was to explore the effects of different concentrations of amoxicillin (AMX) on nitrogen (N) conversion and bacterial community structure during aerobic composting. The results revealed that AMX led to a lower temperature and increased pH during the thermophilic phase of composting. AMX inhibited the relative abundance (RA) of Firmicutes at the initial phase but increased the RA of Actinobacteria and Bacteroidetes compared with the control treatment. The core bacterial community linked to N conversion was determined by network analysis. AMX decreased the RA of amoA, a gene related to nitrification, and increased the RAs of nirK and nosZ, which are related to denitrification. Meanwhile, AMX inhibited the activity of ammonia-oxidizing bacteria but promoted the activity of denitrifying bacteria. Therefore, the main adverse effect of AMX on compost quality is to change the microbial community structure and affect the physical and chemical properties of composting.

Livestock Manure Type Affects Microbial Community Composition and Assembly During Composting

Composting is an environmentally friendly way to turn plant and animal wastes into organic fertilizers. However, it is unclear to what extent the source of animal waste products (such as manure) affects the physicochemical and microbiological properties of compost. Here, we experimentally tested how the type of livestock manure of herbivores (sheep and cattle) and omnivores (pig and chicken) influences the bacterial and fungal communities and physicochemical properties of compost. Higher pH, NO₃-N, Total carbon (TC) content and C/N were found in sheep and cattle manure composts, while higher EC, NH₄-N, Total nitrogen (TN) and total phosphorus (TP) content were measured in pig and chicken manure composts. Paired clustering between herbivore and omnivore manure compost metataxonomy composition was also observed at both initial and final phases of composting. Despite this clear clustering, all communities changed drastically during the composting leading to reduced bacterial and fungal diversity and large shifts in community composition and species dominance. While Proteobacteria and Chloroflexi were the major phyla in sheep and cattle manure composts, Firmicutes dominated in pig and chicken manure composts. Together, our results indicate that feeding habits of livestock can determine the biochemical and biological properties of manures, having predictable effects on microbial community composition and assembly during composting. Manure metataxonomy profiles could thus potentially be used to steer and manage composting processes.

Influence of malonic acid and manganese dioxide on humic substance formation and inhibition of CO2 release during composting

The aim of thisstudy was to explore the effects of malonic acid (MA), manganese dioxide (MnO₂), malonic acid combined with manganese dioxide (MA + MnO₂) additionon reducing CO₂ emission and promoting humic substance (HS) formation during composting. The result showed that the addition of MA and MnO₂ were an efficient way to reduce CO₂ emission. Meanwhile, the CO₂ emissions in the MA + MnO₂ treatment was 36.8% less than that of the CK, and the amount of humic acid (HA) produced in the MnO₂ treatment was 38.7% higher than that of the CK. Structural equation models demonstrated that the addition of exogenoussubstance 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.

Bacterial ecosystem functioning in organic matter biodegradation of different composting at the thermophilic phase

This study aimed to provide insights into prediction of composting ecological functioning through analyzing the critical bacterial populations and functions. The bacterial ecosystem functioning was essential, and cow dung, chicken manure, mushroom dreg and Chinese medicine residues were used as raw materials to quantify and predict the functioning of bacterial communities through synthetic spike-in standards accompanied Illumina sequencing and PICRUSt. Bacterial community of wheat straw and chicken manure compost (SCM) was similar to mushroom dreg and chicken manure compost (MCM), and Sinibacillus dominated in both treatments with the abundance of 20.73% and 41.36%, respectively. The correlation analysis between bacterial community and fluorescence EEM regional integration parameters showed that Lactobacillus (0.889), Enterococcus (0.888) and Erysipelothri (0.903) were positively correlated with P_V, n / P_III, n. The ontology analysis results showed that metabolism, genetic information processing, environmental information processing and cellular processes were the primary functions for bacterial community in all treatments.

Selective pressures of heavy metals on microbial community determine microbial functional roles during composting: Sensitive, resistant and actor

Heavy metals (HM) pollution exerts an effect on microbial community composition and structure during composting, the way how microbial community responses to HM pressure is remain poorly understood though. The aim of this study was to explore functional roles of microorganisms based on selective pressures of HM (Cu, Zn and Cd). The results of microbial resistance showed that the toxicity of metals to microorganisms were Cu > Zn > Cd during composting. Cu and Zn were more toxic for microorganisms during composting when compared with Cd. However, microorganisms had a longer lag period to grow under Zn stress through microbial tolerance determination. In addition, the microbial catalase activity generally decreased and protease activity generally increased, thus microorganisms became more adaptable to HM stress during composting. The experimental results confirmed the existence of sensitive, resistant and actor microorganisms during beef cattle and chicken manures composting. Ultimately, the resistant, sensitive and actor microorganisms at genus level were distinguished under HM pressure based on the network analysis and structural equation models, including 85 resistant microorganisms, 5 sensitive microorganisms and 6 actor microorganisms. This would be helpful to understand the microbial succession process under HM stress and identify functional strains of HM remediation.

Reconstruction of core microbes based on producing lignocellulolytic enzymes causing by bacterial inoculation during rice straw composting

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.

Speciation, toxicity mechanism and remediation ways of heavy metals during composting: A novel theoretical microbial remediation method is proposed

Heavy metals (HM) pollution is a major limitation to the application of composting products. Therefore, mitigating the toxicity of HM has attracted wide attention during composting. The toxicity of HM is mainly acted on microorganisms during composting, and the toxicity of different HM speciation is obviously various. There are many pathways to change the speciation to reduce the toxicity during composting. Therefore, in this review, the speciation distribution, toxicity mechanism and remediation ways of HM during composting were discussed in order to better solve HM pollution. The microbial remediation technology holds enormous potential to remediate for HM without damaging composting, however, it is hard to extract HM. The innovation of this review was to outline microbial remediation strategies for HM during composting based on two mechanisms of microbial remediation: extracellular adsorption and intracellular sequestration, to solve the problem how to extract microbial agents from the compost. Ultimately, a novel theoretical method of microbial remediation was proposed to remove HM from the compost.

Microbial community composition turnover and function in the mesophilic phase predetermine chicken manure composting efficiency

The aim of this work was to study the influence of inoculation with microbial inoculants (MI) or mature compost (MC) by comparing the resultant composting efficiency with that in a noninoculated (CK) treatment. MI and MC application both accelerated the composting process according to fluorescence excitation-emission matrix (EEM) detection and germination index testing. Bacterial and fungal community composition both differed significantly over the composting period. However, the turnover of the initial bacterial community played a significant role in the composting process, and the key operational taxonomic units (OTUs) of MI (OTU_26, Thermicanus) and MC (OTU_48, Tepidimicrobium) showed significant explanatory power for the formation of humic acid-like and fulvic acid-like substances, respectively, during the stage of composting. Thus, our results indicate that microbial inoculation accelerates the composting process by stimulating key resident microbes in the initial stage.

A review of mathematical models for composting

Composting is a valuable method to treat and valorize organic waste. However, the process is defined by its dynamic nature and governed by a multitude of operating parameters. As such, mathematical modelling of the process offers a powerful tool to simulate and predict the variable outcomes of the process, allowing for its optimization. This can include improving efficiency, lowering costs and reducing environmental impact. To aid with the development of future models, we provide an up to date review and assessment on the state of the art of composting modelling. By reviewing 40 years of literature, this review paints the most complete picture of the field to date. This includes an analysis of trends in composting modelling: looking at the type of systems that are targeted, the aim of the models and the approaches to kinetics and mass and heat transfer. Regarding modelling approaches, we explore the fractionation of both substrates and microorganisms, the biological processes that can be included (disintegration, hydrolysis, uptake and death) and their kinetics (first-order, Monod-type), energy balances (biological generation, convection, conduction) and mass balances. We also provide a review of the results of sensitivity analyses performed on composting models, finding that models are most sensitive to microbial growth and death rates, as well as consumption rates and product yields. In the final portion of the review, we identify, explore, and provide guiding recommendations for work on emerging areas and areas requiring development in composting modelling (volume change, pH, maturation, artificial intelligence, etc.).

Passivation of lead and cadmium and increase of the nutrient content during sewage sludge composting by phosphate amendments

As an efficient and cost-effective biological treatment method for sewage sludge, composting has been widely used worldwide. To passivate heavy metals and enhance the nutrient content in compost, in the present study, phosphate rock, calcium magnesium phosphate, and monopotassium phosphate were added to the composting substrate. According to the Community Bureau of Reference sequential extraction procedure, phosphate rock and monopotassium phosphate amendments exhibit a good passivation effect on Cd and Pb. The X-ray diffraction patterns proved the formation of Pb₃(PO₄)₂ and Cd₅(PO₄)₂SiO₄ crystals, and X-ray absorption near-edge structure spectroscopy illustrated the change in P speciation after phosphate amendment. Furthermore, phosphate amendment increased the contents of total P and available P, and it reduced the loss of N during sewage sludge composting. The germination index showed that the target phosphate amendments in sewage sludge compost had no negative effects on seed germination, and this method has great potential to be used as a soil amendment.

Effect of Fenton pretreatment combined with bacteria inoculation on humic substances formation during lignocellulosic biomass composting derived from rice straw

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.

Identifying the action ways of function materials in catalyzing organic waste transformation into humus during chicken manure composting

The aim of this study is to detect the action properties of functional materials (FM) in transforming waste into resource products with high humus content. FM (MnO₂ and reducing sugar) were added in different periods of chicken manure composting. During composting, concentration of humic acids (HA) as aromatic fraction of humus, was increased by FM. The promotive effects of adding FM in later period was the most obvious. While adding FM in the beginning period could accelerate organic matter degradation, but it did not promote HA formation. Meanwhile, the microbial diversity was higher in groups by adding FM in the beginning and thermophilic periods. Therefore, it was speculated that FM might improve HA formation by promoting the abiotic polymerization of precursors. Eventually, structural equation model showed that FM was beneficial to abiotic pathway of HA formation. But the formation efficiency was reduced by interfering with biotic pathway.

Effect of fine coal gasification slag on improvement of bacterial diversity community during the pig manure composting

In present study, evaluate the effect of fine coal gasification slag (FCGS) as additive on abundance of bacterial diversity during pig manure composting. The six different dosages of FCGS 0% (T1), 2% (T2), 4% (T3), 6% (T4), 8% (T5) and 10% (T6) (dry weight basis) were mixed with original raw materials for 42 days an aerobic composting. The results indicated that FCGS adopted could affect the succession of bacterial diversity in different ways. Among all treatments, Firmicutes, Proteobacteria, Tenericutes, unidentified_Bacteria, and Actinobacteria were the highest abundance in weighted unifrac distance but Firmicutes; Proteobacteria, Actinobacteria, Bacteroidetes, and Spirochaetes were main bacteria in unweighted unifrac distance. The β-diversity and principal component analysis indicated a significant difference in bacterial diversity in all treatments which T4 obtained difference obviously. Therefore, the results showed that T4 was a potential candidate to enhance significantly abundance of bacterial community in PM compost.

A novel method for removing heavy metals from composting system: The combination of functional bacteria and adsorbent materials

The aim of this study was to remove heavy metals from composting system using a novel method combined functional bacteria with adsorbent materials. Four types of adsorbent materials were selected in this study. Results showed that Cr had significant removal efficiency, especially in sponge treatment (19.09%) and cotton treatment (26.36%). In addition, a significant movement of heavy metals from the outside to adsorbent column was also observed. RDA results indicated that bands 1, 2, 10, 18, 19 and 20 had negative correlations with six types of heavy metals, which contributed to the removal of heavy metals. Structural equation models further confirmed functional bacteria can directly affect the removal of Cu, Cd and Cr. In addition, it can also indirectly remove Pb and Cr by changing native bacteria. In summary, this study suggested the combination of functional bacteria and adsorbent materials was effective to remove heavy metals from composting system.

Roles of adding biochar and montmorillonite alone on reducing the bioavailability of heavy metals during chicken manure composting

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.

Recognition of the neutral sugars conversion induced by bacterial community during lignocellulose wastes composting

The aim of this study was to explore the conversion characteristics of neutral sugars during different lignocellulose wastes composting from rice straw (RS), leaf (L) and mushroom dreg (MD). The results showed that the changes of neutral sugars were different during different wastes composting, but the changes of various hexose or pentose were similar during composting of the same material. The diversity of bacterial community led to different conversion characteristics of neutral sugars. During RS composting, each neutral sugar was transformed by a specific group of bacteria. However, a group of bacteria could transform multiple neutral sugars during MD and L composting. Furthermore, GM/AX value was first applied to composting, which could be used to characterize the conversion of neutral sugars during composting. This will help to provide more efficient recommendations for lignocellulose wastes treatment and accelerating humic substances synthesis during composting.

Effect of tricarboxylic acid cycle regulators on the formation of humic substance during composting: The performance in labile and refractory materials

The aims of this study are to reveal the roles of tricarboxylic acid (TCA) cycle regulators in reducing CO₂ emission and promoting humic substance (HS) formation during composting with different materials. The results showed that the addition of adenosine tri-phosphate (ATP) or malonic acid (MA) reduced CO₂ emission during chicken manure composting. However, only the addition of MA reduced CO₂ emission during lawn waste and garden waste composting. In addition, both of the two inhibitors promoted HS formation, especially for ATP. Structural equation models further confirmed that ATP and MA reduced CO₂ emission by inhibiting the decomposition of amino acid by microorganisms. Meanwhile, ATP promoted the conversion of amino acid and soluble sugars to HS, while MA only promoted the conversion of soluble sugars to HS. In summary, this study provides a theoretical basis for the application of inhibitors to reduce CO₂ emission and promote HS formation during composting.

Effects of exogenous protein-like precursors on humification process during lignocellulose-like biomass composting: Amino acids as the key linker to promote humification process

The aim of this study is to assess the effectiveness of protein-like precursors addition on promoting humification process during lignocellulose-like biomass composting through adding amino acids to compost. The humification indexes of R1 and R2 was significantly higher than that of CK (P < 0.05). The decreasing ratio of Maillard precursor concentration of R2 and R1 was higher than CK. Amino acids addition affected the bacteria community and environmental factors during composting. Variance partitioning analysis showed that humification process was strengthened with environmental factors, bacteria community, Maillard precursors. Structural equation model (SEM) analysis showed that amino acids had substantial impact on promoting humic acid (HA) formation. The combined application of protein-like wastes and lignocellulose-like wastes was suggested to improve carbon sequestration. This study lays a foundation for economically and effectively managing different types of straws by composting.

Assessment contributions of physicochemical properties and bacterial community to mitigate the bioavailability of heavy metals during composting based on structural equation models

The aim of this study was to explore the pathways to mitigate the bioavailability of heavy metals (HM) during chicken and beef cattle manures composting. For raw materials, HM contents in animal manures from breeding farm were 1.5-3 times as much as that of domestic animal manures. Structural equation models (SEMs) based on denaturing gradient gel electrophoresis (DGGE) showed that mitigating bioavailability of HM was mainly attributed to physicochemical properties (organic matters content and temperature) during beef cattle manures composting. However, both physicochemical properties (organic matters content, temperature, pH and moisture) and bacterial community were critical factors during chicken manures composting. Furthermore, the statistical analysis from high-throughput sequencing verified the results of SEMs. Therefore, the bioavailability of HM will be mitigated by different deactivation pathways according to diverse raw materials composting.

Roles of bacterial community in the transformation of organic nitrogen toward enhanced bioavailability during composting with different wastes

This study aimed to explore the roles of bacterial community in the transformation of bioavailable organic-N (BON) during different wastes composting. BON fractions with different forms and molecular weights were identified in this study. Results indicated that core bacterial communities improved the availability of BON by degrading high molecular weights BON into low molecular weights BON during different wastes composting. A total of fifty-two core bacterial genera involved in BON transformation were identified by network analysis. Three types of high molecular weights BON fractions (amino acid-N, amine-N and amino sugar-N) were degraded by bacteria during chicken manure and garden waste composting, while only amine-N was degraded during municipal solid waste composting. Finally, moisture, C/N and pH were identified as the key operational parameters affecting BON transformation mediated by microorganisms, which can be used to improve bioavailability of organic-N and reduce N loss during composting.

Host bacterial community of MGEs determines the risk of horizontal gene transfer during composting of different animal manures

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, NH₄⁺, NO₃^- 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.