Effects of microbial culture and chicken manure biochar on compost maturity and greenhouse gas emissions during chicken manure composting

Dynamics of antibiotic resistance genes during manure composting: Reduction in herbivores manure and accumulation in carnivores

The elevated levels of antibiotic resistance genes (ARGs) in livestock manure represent a significant threat to both the environment and human health. Composting has been recognized as an effective strategy to mitigate the abundance of ARGs in manure. However, notable rebounds in ARGs abundance have been observed during this process. This study explored the changes in ARGs abundance and the underlying influencing factors during the composting of carnivore (chicken and pig) and herbivore (sheep and cow) manures, along with mushroom residues. The findings revealed that the total relative abundance of ARGs increased by 6.96 and 10.94 folds in chicken and pig manure composts, respectively, whereas it decreased by a remarkable 91.72% and 98.37% in sheep and cow manure composts. Nitrogen content emerged as the primary physicochemical factors governing the abundance of ARGs in chicken and pig manure composts. Conversely, carbon content played a pivotal role in determining ARGs abundance in chicken and pig manure composts. Furthermore, the presence of dominant hosts, such as Corynebacterium, Bacillus, and Clostridium, along with emerging bacteria like Thermobifida, Saccharomonospora, and Actinomadura, contributed significantly to the enrichment of total ARGs, including tetG, tetO, tetX, and sul2, in chicken and pig manure composts. The coexistence of these genes with mobile genetic elements and a plethora of host bacteria, coupled with their high abundance, renders them particularly high-risk ARGs. On the other hand, the observed decrease in the abundance of total ARGs in sheep and cow manure composts can be attributed to the decline in the population of host bacteria, specifically Atopostipes, Psychrobacter, and Corynebacterium. Collectively, these results provide crucial insights into the management of ARGs risks and offer essential theoretical support for enhancing the safe utilization of organic fertilizer in agriculture.

The production of methyl mercaptan is the main odor source of chicken manure treated with a vertical aerobic fermenter

The process of harmless treatment of livestock manure produces a large amount of odor, which poses a potential threat to human and livestock health. A vertical fermentation tank system is commonly used for the environmentally sound treatment of chicken manure in China, but the composition and concentration of the odor produced and the factors affecting odor emissions remain unclear. In this study, we investigated the types and concentrations of odors produced in the mixing room (MR), vertical fermenter (VF), and aging room (AR) of the system, and analyzed the effects of bacterial communities and metabolic genes on odor production. The results revealed that 34, 26 and 26 odors were detected in the VF, MR and AR, respectively. The total odor concentration in the VF was 66613 ± 10097, which was significantly greater than that in the MR (1157 ± 675) and AR (1143 ± 1005) (P < 0.001), suggesting that the VF was the main source of odor in the vertical fermentation tank system. Methyl mercaptan had the greatest contribution to the odor produced by VF, reaching 47.82%, and the concentration was 0.6145 ± 0.2164 mg/m3. The abundance of metabolic genes did not correlate significantly with odor production, but PICRUSt analysis showed that cysteine and methionine metabolism involved in methyl mercaptan production was significantly more enriched in MR and VF than in AR. Bacillus was the most abundant genus in the VF, with a relative abundance significantly greater than that in the MR (P < 0.05). The RDA results revealed that Bacillus was significantly and positively correlated with methyl mercaptan. The use of large-scale aerobic fermentation systems to treat chicken manure needs to focused on the production of methyl mercaptan.

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

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

Modern perspectives of heavy metals alleviation from oil contaminated soil: A review

Heavy metal poisoning of soil from oil spills causes serious environmental problems worldwide. Various causes and effects of heavy metal pollution in the soil environment are discussed in this article. In addition, this study explores new approaches to cleaning up soil that has been contaminated with heavy metals as a result of oil spills. Furthermore, it provides a thorough analysis of recent developments in remediation methods, such as novel nano-based approaches, chemical amendments, bioremediation, and phytoremediation. The objective of this review is to provide a comprehensive overview of the removal of heavy metals from oil-contaminated soils. This review emphasizes on the integration of various approaches and the development of hybrid approaches that combine various remediation techniques in a synergistic way to improve sustainability and efficacy. The study places a strong emphasis on each remediation strategy that can be applied in the real-world circumstances while critically evaluating its effectiveness, drawbacks, and environmental repercussions. Additionally, it discusses the processes that reduce heavy metal toxicity and improve soil health, taking into account elements like interactions between plants and microbes, bioavailability, and pollutant uptake pathways. Furthermore, the current study suggests that more research and development is needed in this area, particularly to overcome current barriers, improve our understanding of underlying mechanisms, and investigate cutting-edge ideas that have the potential to completely transform the heavy metal clean up industry.

Evaluation of gases emission and enzyme dynamics in sheep manure compost occupying with peach shell biochar

The effect of peach shell biochar (PSB) amendment on sheep manure (SM) composting was investigated. Five different ratios of PSB were applied (0%, 2.5%, 5%, 7.5%, and 10% PSB), and named T1 to T5, and run 50 days of composting experiment. It was found that PSB (especially 7.5% and 10%) could improve the compost environment, regulate the activity of microorganisms and related enzymes, and promote the decomposition of compost. 7.5% and 10% PSB advanced the heap into the thermophilic stage and increased the maximum temperature, while also increasing the germination index by 1.40 and 1.39 times compared to control. Importantly, 10% PSB effectively retained more than 60% of carbon and 55% of nitrogen by inhibiting the excess release of NH3 and greenhouse gases. High proportion PSB amendment increased the activity of dehydrogenase and cellulase, but inhibited protease and urease. The correlation results indicated that PSB changed the key bacterial genus, and there was a stronger association with environmental factors at 7.5% and 10%. Therefore, 7.5% and 10% peach shell biochar can be used as appropriate proportions to improve composting conditions.

Ecological consequences of biochar and hydrochar amendments in soil: assessing environmental impacts and influences

Anthropogenic activities have caused irreversible consequences on our planet, including climate change and environmental pollution. Nevertheless, reducing greenhouse gas (GHG) emissions and capturing carbon can mitigate global warming. Biochar and hydrochar are increasingly used for soil remediation due to their stable adsorption qualities. As soil amendments, these materials improve soil quality and reduce water loss, prevent cracking and shrinkage, and interact with microbial communities, resulting in a promising treatment method for reducing gas emissions from the top layer of soil. However, during long-term studies, contradictory results were found, suggesting that higher biochar application rates led to higher soil CO2 effluxes, biodiversity loss, an increase in invasive species, and changes in nutrient cycling. Hydrochar, generated through hydrothermal carbonization, might be less stable when introduced into the soil, which could lead to heightened GHG emissions due to quicker carbon breakdown and increased microbial activity. On the other hand, biochar, created via pyrolysis, demonstrates stability and can beneficially impact GHG emissions. Biochar could be the preferred red option for carbon sequestration purposes, while hydrochar might be more advantageous for use as a gas adsorbent. This review paper highlights the ecological impact of long-term applications of biochar and hydrochar in soil. In general, using these materials as soil amendments helps establish a sustainable pool of organic carbon, decreasing atmospheric GHG concentration and mitigating the impacts of climate change.

From waste to protein: a new strategy of converting composted distilled grain wastes into animal feed

Distilled grain waste (DGW) is rich in nutrients and can be a potential resource as animal feed. However, DGW contains as much as 14% lignin, dramatically reducing the feeding value. White-rot fungi such as Pleurotus ostreatus could preferentially degrade lignin with high efficiency. However, lignin derivatives generated during alcohol distillation inhibit P. ostreatus growth. Thus, finding a new strategy to adjust the DGW properties to facilitate P. ostreatus growth is critical for animal feed preparation and DGW recycling. In this study, three dominant indigenous bacteria, including Sphingobacterium thermophilum X1, Pseudoxanthomonas byssovorax X3, and Bacillus velezensis 15F were chosen to generate single and compound microbial inoculums for DGW composting to prepare substrates for P. ostreatus growth. Compared with non-inoculated control or single microbial inoculation, all composite inoculations, especially the three-microbial compound, led to faster organic metabolism, shorter composting process, and improved physicochemical properties of DGW. P. ostreatus growth assays showed the fastest mycelial colonization (20.43 μg·g-1 ergosterol) and extension (9 mm/d), the highest ligninolytic enzyme activities (Lac, 152.68 U·g-1; Lip, 15.56 U·g-1; MnP, 0.34 U·g-1; Xylanase, 10.98 U·g-1; FPase, 0.71 U·g-1), and the highest lignin degradation ratio (30.77%) in the DGW sample after 12 h of composting with the three-microbial compound inoculation when compared to other groups. This sample was relatively abundant in bacteria playing critical roles in amino acid, carbohydrate, energy metabolism, and xenobiotic biodegradation, as suggested by metagenomic analysis. The feed value analysis revealed that P. ostreatus mycelia full colonization in composted DGW led to high fiber content retention and decreased lignin content (final ratio of 5% lignin) but elevated protein concentrations (about 130 g·kg-1 DM). An additional daily weight gain of 0.4 kg/d was shown in cattle feeding experiments by replacing 60% of regular feed with it. These findings demonstrate that compound inoculant consisting of three indigenous microorganisms is efficient to compost DGW and facilitate P. ostreatus growth. P. ostreatus decreased the lignin content of composted DGW during its mycelial growth, improving the quality of DGW for feeding cattle.

Effect of different bulking agents on fed-batch composting and microbial community profile

The current study focused on analyzing the effect of different types of bulking agents and other factors on fed-batch composting and the structure of microbial communities. The results indicated that the introduction of bulking agents to fed-batch composting significantly improved composting efficiency as well as compost product quality. In particular, using green waste as a bulking agent, the compost products would achieve good performance in the following indicators: moisture (3.16%), weight loss rate (85.26%), and C/N ratio (13.98). The significant difference in moisture of compost products (p < 0.05) was observed in different sizes of bulking agent (green waste), which was because the voids in green waste significantly affected the capacity of the water to permeate. Meanwhile, controlling the size of green waste at 3-6 mm, the following indicators would show great performance from the compost products: moisture (3.12%), organic matter content (63.93%), and electrical conductivity (EC) (5.37 mS/cm). According to 16S rRNA sequencing, the relative abundance (RA) of thermophilic microbes increased as reactor temperature rose in fed-batch composting, among which Firmicutes, Proteobacteria, Basidiomycota, and Rasamsonia were involved in cellulose and lignocellulose degradation.

Effects of two strains of thermophilic nitrogen-fixing bacteria on nitrogen loss mitigation in cow dung compost

Excavating nitrogen-fixing bacteria with high-temperature tolerance is essential for the efficient composting of animal dung. In this study, two strains of thermophilic nitrogen-fixing bacteria, NF1 (Bacillus subtilis) and NF2 (Azotobacter chroococcum), were added to cow dung compost both individually (NF1, NF2) and mixed together (NF3; mixing NF1 and NF2 at a ratio of 1:1). The results showed that NF1, NF2, and NF3 inoculants increased the total Kjeldahl nitrogen level by 38.43%-55.35%, prolonged the thermophilic period by 1-13 d, increased the seed germination index by 17.81%, and the emissions of NH3 and N2O were reduced by 25.11% and 42.75%, respectively. Microbial analysis showed that Firmicutes were the predominant bacteria at the thermophilic stage, whereas Chloroflexi, Proteobacteria, and Bacteroidetes were the predominant bacteria at the mature stage. These results confirmed that the addition of the isolated strains to cow dung composting improved the bacterial community structure and benefited nitrogen retention.

Integrating bioprocess and metagenomics studies to enhance humic acid production from rice straw

Rice straw burning annually (millions of tons) leads to greenhouse gas emissions, and an alternative solution is producing humic acid with high added-value. This study aimed to examine the influence of a microbial consortium and other additives (chicken manure, urea, olive mill waste, zeolite, and biochar) on the composting process of rice straw and the subsequent production of humic acid. Results showed that among the fungal species, Thermoascus aurantiacus exhibited the most prominent impact in expediting maturation and improving compost quality, and Bacillus subtilis was the most abundant bacterial species based on metagenomics analysis. The highest temperature, C/N ratio reduction, and amount of humic acid production (Respectively in lab 61 °C, 54.67%, 298 g kg-1 and in pilot level 65 °C, 72.11%, 310 g kg-1) were related to treatments containing these microorganisms and other additives except urea. Consequently, T. aurantiacus and B. subtilis can be employed on an industrial scale as compost additives to further elevate quality. Functional analysis showed that the bacterial enzymes in the treatments had the highest metabolic activities, including carbohydrate and amino acid metabolism compared to the control. The maximum enzymatic activities were in the thermophilic phase in treatments which were significantly higher than that in the control. The research emphasizes the importance of identifying and incorporating enzymatically active strains that are suitable for temperature conditions, alongside the native strains in decomposing materials. This strategy significantly improves the composting process and yields high-quality humic acid during the thermophilic phase.

Different crystalline manganese dioxide and biochar co-conditioning aerobic composting: Reduced ammonia volatilization and improved organic fertilizer quality

Aerobic composting is a sustainable and effective waste disposal method. However, it can generate massive amounts of ammonia (NH3) via volatilization. Effectively reducing NH3 volatilization is vital for advancing aerobic composting and protecting the ecological environment. Herein, two crystal types of MnO2 (α-MnO2 and δ-MnO2) are combined with biochar (hydrochar (WHC) and pyrochar (WPC), respectively) and used as conditioners for the aerobic composting of chicken manure. Results reveal that α-MnO2 (34.6%) can more effectively reduce NH3 accumulation than δ-MnO2 (27.1%). Moreover, the combination of WHC and MnO2 better reduces NH3 volatilization (48.5-58.9%) than the combination of WPC and MnO2 (15.8-40.1%). The highest NH3 volatilization reduction effect (58.9%) is achieved using the combination of WHC and δ-MnO2. Because the added WHC and δ-MnO2 promote the humification of the compost, the humic acid to fulvic acid ratio (HA/FA ratio) dramatically increases. The combination of WHC and δ-MnO2 doubled the HA/FA ratio and resulted in a net economic benefit of 130.0 RMB/t. Therefore, WHC and δ-MnO2 co-conditioning can promote compost decomposition, improving the quality of organic fertilizers and substantially reducing NH3 volatilization.

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

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

Potential of novel iron 1,3,5-benzene tricarboxylate loaded on biochar to reduce ammonia and nitrous oxide emissions and its associated biological mechanism during composting

In this study, a novel iron 1,3,5-benzene tricarboxylate loaded on biochar (BC-FeBTC) was developed and applied to kitchen waste composting. The results demonstrated that the emissions of NH3 and N2O were significantly reduced by 57.2% and 37.8%, respectively, compared with those in control group (CK). Microbiological analysis indicated that BC-FeBTC addition altered the diversity and abundance of community structure as well as key functional genes. The nitrification genes of ammonia-oxidizing bacteria were enhanced, thereby promoting nitrification and reducing the emission of NH3. The typical denitrifying bacterium, Pseudomonas, and critical functional genes (nirS, nirK, and nosZ) were significantly inhibited, contributing to reduced N2O emissions. Network analysis further revealed the important influence of BC-FeBTC in nitrogen transformation driven by functional microbes. These findings offer crucial scientific foundation and guidance for the application of novel materials aimed at mitigating nitrogen loss and environmental pollution during composting.

The maturity, humus content, and microbial metabolic function of sheep manure compost on the Qinghai-Tibet Plateau can be significantly improved by reducing the moisture content

The Qinghai-Tibet Plateau (QTP) is characterized by an extreme hypoxia, which may lead to lack of sufficient oxygen for compost production, and thus seriously affecting the compost quality. The moisture content (MC) has a direct effect on the oxygen content of composting pile. At present, the research on the optimum moisture content of compost production on the QTP is still lacking. This study aimed to investigate the influences of MC on fermentation quality of sheep manure composting on the QTP and to further analyze the changes of microbial metabolic function and enzyme activity under different MC. Composting experiment with low MC (45%) and conventional MC (60%) was conducted in both summer and autumn. The results showed that the composting efficiency of 45% MC was better than 60% in both seasons, which was mainly manifested as longer high-temperature period (summer:16 d vs 14 d, autumn: 7 d vs 2 d), higher germination index (summer:136.1% vs 128.6%, autumn:103.5% vs 81.2%), and more humus synthesis (summer:159.8 g/kg vs 151.2 g/kg, autumn:136.1 k/kg vs 115.5 k/kg). The 45% MC can improve microbial metabolism, including increasing the abundance of functional genes involved in carbohydrate metabolism, amino acid metabolism, and nucleotide metabolism and improving the activities of cellulase, β-glucosidase, protease, polyphenol oxidase, and peroxidase. In conclusion, 45% MC can improve the fermentation efficiency and products quality of sheep manure compost on QTP.

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

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

Effect of microbial inoculum on composting efficiency in the composting process of spent mushroom substrate and chicken manure

This work aimed to investigate the microbial mechanisms for the improvement of composting efficiency driven by the compound microbial inoculum (MI) (Bacillus subtilis SL-44, Enterobacter hormaechei Rs-189 and Trichoderma reesei) during co-composting of spent mushroom substrate (SMS) and chicken manure (CM). The treatments used in the study were as follows: 1) MI (inoculation with microbial inoculum), 2) CI (inoculation with commercial microbial inoculum), and 3) CK (without inoculation). The results demonstrated that MI increased the seed germination index (GI) by 25.11%, and contents of humus, humic acid (HA) and available phosphorus (AP) were correspondingly promoted by 12.47%, 25.93% and 37.16%, respectively. The inoculation of MI increased the temperature of the thermophilic stage by 3-7 °C and achieved a cellulose degradation rate of 52.87%. 16S rRNA gene analysis indicated that Actinobacteria (11.73-61.61%), Firmicutes (9.46-65.07%), Proteobacteria (2.86-32.17%) and Chloroflexi (0.51-10.92%) were the four major phyla during the inoculation composting. Bacterial metabolic functional analysis revealed that pathways involved in amino acid and glycan biosynthesis and metabolism were boosted in the thermophilic phase. There was a positive correlation between bacterial communities and temperature, humification and phosphorus fractions. The average dry weight, fresh weight and seedling root length in the seedling substrates adding MI compost were 1.13, 1.23 and 1.06 times higher than those of the CK, respectively. This study revealed that biological inoculation could improve the composting quality and efficiency, potentially benefiting the resource utilization of agricultural waste resources.

NH3 and greenhouse gas emissions during co-composting of lignite and poultry wastes and the following amendment of co-composted products in soil

Ammonia (NH3) and greenhouse gas (GHG) emissions are substantial contributors to C and N loss in composting. Lignite can increase N retention by absorbing N H 4 + and NH3. However, the effects of co-composting on NH3 and GHG emissions in view of closing nutrient cycle are still poorly investigated. In the study, poultry litter was composted without (CK) or with lignite (T1) or dewatered lignite (T2), and their respective composts N H 4 + Com_CK, Com_T1, and Com_T2) were tested in a soil incubation to assess NH3 and GHG emission during composting and following soil utilization. The cumulative NH3 flux in T1 and T2 were reduced by 39.3% and 50.2%, while N2O emissions were increased by 7.5 and 15.6 times, relative to CK. The total GHG emission in T2 was reduced by 16.8% compared to CK. Lignite addition significantly increased nitrification and denitrification as evidenced by the increased abundances of amoA, amoB, nirK, and nirS. The increased reduction on NH3 emission by dewatered lignite could be attributed to reduced pH and enhanced cation exchangeable capacity than lignite. The increased N2O was related to enhanced nitrification and denitrification. In the soil incubation experiment, compost addition reduced NH3 emission by 72%∼83% while increased emissions of CO2 and N2O by 306%∼740% and 208%∼454%, compared with urea. Com_T2 strongly reduced NH3 and GHG emissions after soil amendment compared to Com_CK. Overall, dewatered lignite, as an effective additive, exhibits great potential to simultaneously mitigate NH3 and GHG secondary pollution during composting and subsequent utilization of manure composts.

Composting municipal solid waste and animal manure in response to the current fertilizer crisis - a recent review

The dynamic price increases of fertilizers and the generation of organic waste are currently global issues. The growth of the population has led to increased production of solid municipal waste and a higher demand for food. Food production is inherently related to agriculture and, to achieve higher yields, it is necessary to replenish the soil with essential minerals. A synergistic approach that addresses both problems is the implementation of the composting process, which aligns with the principles of a circular economy. Food waste, green waste, paper waste, cardboard waste, and animal manure are promising feedstock materials for the extraction of valuable compounds. This review discusses key factors that influence the composting process and compares them with the input materials' parameters. It also considers methods for optimizing the process, such as the use of biochar and inoculation, which result in the production of the final product in a significantly shorter time and at lower financial costs. The applications of composts produced from various materials are described along with associated risks. In addition, innovative composting technologies are presented.

Malonic acid shapes bacterial community dynamics in compost to promote carbon sequestration and humic substance synthesis

The incorporation of malonic acid (MA) into compost as a regulator of the tricarboxylic acid (TCA) cycle has the potential to increase carbon sequestration. However, the influence of MA on the transformation of the microbial community during the composting process remains unclear. In this investigation, MA was introduced at different stages of chicken manure (CM) composting to characterize the bacterial community within the compost using high-throughput sequencing. We assess the extent of increased carbon sequestration by comparing the concentration of total organic carbon (TOC). At the same time, this study examines whether increased carbon sequestration contributes to humus formation, which was elucidated by evaluating the content and composition of humus. Our results show that the addition of MA significantly improved carbon sequestration within the compost, reducing the carbon loss rate (C loss (%)) from 64.70% to 52.94%, while increasing HS content and stability. High throughput sequencing and Random Forest (RF) analysis show that the introduction of MA leads to a reduction in the diversity of the bacterial communities, but enhanced the ability of bacterial communities to synthesize humus. Furthermore, the addition of MA favors the proliferation of Firmicutes. Also, the hub of operational taxonomic units (OTUs) within the community co-occurrence network shifts from Proteobacteria to Firmicutes. Remarkably, our study finds a significant decrease in negative correlations between bacteria, potentially mitigating substrate consumption due to negative interactions such as competition. This phenomenon contributes to the improved retention of TOC in the compost. This research provides new insights into the mechanisms by which MA regulates bacterial communities in compost, and provides a valuable theoretical basis for the adoption of this innovative composting strategy.

Change of core microorganisms and nitrogen conversion pathways in chicken manure composts by different substrates to reduce nitrogen losses

Due to the rapid development of animal husbandry, the associated environmental problems cannot be ignored, with the management of livestock and poultry manure emerging as the most prominent issue. Composting technology has been widely used in livestock and poultry manure management. A deeper understanding of the nitrogen conversion process during composting offers a theoretical foundation for selecting compost substrates. In this study, the effects of sawdust (CK) and spent mushroom compost (T1) as auxiliary materials on nitrogen as well as microbial structure in the composting process when composted with chicken manure were investigated. At the end of composting, the nitrogen loss of T1 was reduced by 17.18% relative to CK. When used as a compost substrate, spent mushroom compost accelerates the succession of microbial communities within the compost pile and alters the core microbial communities within the microbial community. Bacterial genera capable of cellulose degradation (Fibrobacter, Herbinix) are new core microorganisms that influence the assimilation of nitrate reduction during compost maturation. Using spent mushroom compost as a composting substrate increased the enzyme activity of nitrogen assimilation while decreasing the enzyme activity of the denitrification pathway.

Optimization of organic solid waste composting process through iron-related additives: A systematic review

Composting is an environmentally friendly method that facilitates the biodegradation of organic solid waste, ultimately transforming it into stable end-products suitable for various applications. The element iron (Fe) exhibits flexibility in form and valence. The typical Fe-related additives include zero-valent-iron, iron oxides, ferric and ferrous ion salts, which can be targeted to drive composting process through different mechanisms and are of keen interest to academics. Therefore, this review integrated relevant literature from recent years to provide more comprehensive overview about the influence and mechanisms of various Fe-related additives on composting process, including organic components conversion, humus formation and sequestration, changes in biological factors, stability and safety of composting end-products. Meanwhile, it was recommended that further research be conducted on the deep action mechanisms, biochemical pathways, budget balance analysis, products stability and application during organic solid waste composting with Fe-related additives. This review provided guidance for the subsequent targeted application of Fe-related additives in compost, thereby facilitating cost reduction and promoting circular economy objectives.

Relationships between different types of biochar and N2O emissions during composting based on roles of nosZ-carrying denitrifying bacterial communities enriched on compost and biochar particles

Biochar has demonstrated the potential in mitigating N2O emissions during composting. However, little is known about how microbial communities on biochar particles interact with N2O emissions. This study selected three types of biochar (corn stalk biochar (CSB), rape straw biochar (RSB), and bamboo charcoal (BC)) to investigate the relationship between N2O emissions and denitrifying bacterial communities on compost and biochar particles. The results showed that N2O emissions rate were higher in the thermophilic phase, and the average emissions rate of BC treatment were lower 40% and 26% than CSB and RSB, respectively. The nosZ-carrying denitrifying bacterial community played a key role in reducing N2O emissions, and the network indicated that Rhizobium and Paracoccus on compost particles may have played major roles in reducing N2O emissions, but only Paracoccus on biochar particles. Notably, BC enhanced the efficiency of N2O emission reduction by enhancing the abundance of these key genera.

Enhanced humus synthesis from Chinese medicine residues composting by lignocellulose-degrading bacteria stimulation: Upregulation of key enzyme activity and neglected indirect effects on humus formation

Chinese medicine residues (CMHRs) resource is attracting widespread attention, as it is expected to be produced into Humus-rich fertilizer for soil application. This study aimed to promote effective humus (HS) production through lignocellulose-degrading bacteria (LDB) addition and explore the biological regulation mechanism of LDB affecting lignocellulose-to-humus conversion. The results showed higher HS production was achieved, with 109.73 and 111.44 g·kg-1, and HA/FA was raised by 12.70-16.02 % in compost products by LDB addition stimulation. Significant upregulation of β-glucanase and xylanase activities catalyzed higher decomposition of lignocellulose toward more HS potential precursors supply. Furthermore, exogenous LDB intervention induced microbial community restructure and microbial network establishment via enriching synergism functional bacteria, i.e., Thermobifida, Paenibacillus, Nonomuraea, etc. Mantel test results showed that it was variation of cellulose, hemicellulose and HS that affected microbial community succession (p < 0.01, r > 0.6), which represented the positive action of LDB addition stimulation on HS synthesis upregulation. Further exploration suggested LDB had an indirect effect on HS formation by enhanced lignin and hemicellulose conversion based on the Random Forest model and Partial least-squares path modeling results. This research provides new insights into the trigger effects of LDB introduction on upregulating HS synthesis and is expected to propose new perspectives for HS efficient production in CMHRs composting.

Electric field-assisted aerobic co-composting of chicken manure and kitchen waste: Ammonia mitigation and maturation enhancement

A low-voltage electric field assisted strategy is considered to be effective in improving compost effect of conventional chicken manure composting (CCMC), but it lacks a critical assessment of NH3 mitigation and suitability for complex initial materials. This study firstly constructed an electric field-assisted aerobic co-composting (EFAC) of chicken manure and kitchen waste to evaluate NH3 mitigation and compost maturity. The results showed that the NH3 emissions of EFAC were 48.73% lower than those of CCMC. The proposed mechanisms suggest that the combined effect of reduced acidity and electric field inhibited the activities and functions related to ammoniation and ammonia-nitrogen conversion. The germination index of EFAC was 54.29% higher than that of CCMC, due to the enhancement of compost maturation. This study demonstrates that the electric field-assisted strategy for co-composting has a broad potential to reduce ammonia emissions and enhance the disposal of complex feedstocks.

Nitrogen-enriched biochar co-compost for the amelioration of degraded tropical soil

Tropical soils are often deeply weathered and vulnerable to degradation having low pH and unfavorable Al/Fe levels, which can constrain crop production. This study aims to examine nitrogen-enriched novel biochar co-composts prepared from rice straw, maize stover, and gram residue in various mixing ratios of the biochar and their feedstock materials for the amelioration of acidic tropical soil. Three pristine biochar and six co-composts were prepared, characterized, and evaluated for improving the chemical and biological quality of the soil against a conventional lime treatment. The pH, cation exchange capacity (CEC), calcium carbonate equivalence (CCE) and nitrogen content of co-composts varied between 7.78-8.86, 25.3-30.5 cmol (p+) kg-1, 25.5-30.5%, and 0.81-1.05%, respectively. The co-compost prepared from gram residue biochar mixed with maize stover at a 1:7 dry-weight ratio showed the highest rise in soil pH and CEC, giving an identical performance with the lime treatment and significantly better effect (p < .05) than the unamended control. Agglomerates of calcite and dolomite in biochar co-composts, and surface functional groups contributed to pH neutralization and increased CEC of the amended soil. The co-composts also significantly (p < .05) increased the dehydrogenase (1.87 µg TPF g-1 soil h-1), β-glucosidase (90 µg PNP g-1 soil h-1), and leucine amino peptidase (3.22 µmol MUC g-1 soil h-1) enzyme activities in the soil, thereby improving the soil's biological quality. The results of this study are encouraging for small-scale farmers in tropical developing countries to sustainably reutilize crop residues via biochar-based co-composting technology.

Enhanced removal of antibiotic resistance genes during chicken manure composting after combined inoculation of Bacillus subtilis with biochar

This study explored the combined effects of Bacillus subtilis inoculation with biochar on the evolution of bacterial communities, antibiotic resistance genes (ARGs), and mobile genetic elements (MGEs) during the composting of chicken manure. The results showed that B. subtilis inoculation combined with biochar increased bacterial abundance and diversity as well as prolonged the compost thermophilic period. Promoted organic matter biodegradation and facilitated the organic waste compost humification process, reduced the proliferation of ARGs by altering the bacterial composition. Firmicutes and Actinobacteriota were the main resistant bacteria related to ARGs and MGEs. The decrease in ARGs and MGEs was associated with the reduction in the abundance of related host bacteria. Compost inoculation with B. subtilis and the addition of biochar could promote nutrient transformation, reduce the increase in ARGs and MGEs, and increase the abundance of beneficial soil taxa.

Quantifying direct CO2 emissions from organic manure fertilizer and maize residual roots using 13C labeling technique: A field study

Organic manure compost offers benefits like enhanced crop yield, improved soil health, and increased soil carbon storage. However, its application might elevate direct CO2 emissions from organic matter decomposition. Beyond manure compost, significant sources of CO2 emissions in agricultural settings are from residual roots and root exudates of pre-crops, and soil carbon. Quantifying the contribution of these sources to CO2 emissions is crucial for maximizing carbon reduction in crop-livestock systems, yet field studies have not assessed this contribution. Our study at the Yucheng field station in Shandong Province, China employed 13C labeling on summer maize to generate 13C-labeled manure compost and maize root, which is used to differentiate CO2 emissions from these sources. Our results revealed novel insights into the magnitude and patterns of CO2 emissions from these sources. The emission pattern of 13C-CO2 derived from manure compost, root and root exudates was similar, but the magnitude differed. Specifically, manure compost accounted for 5 % of the total CO2 emissions, while residual roots and root exudates contributed 2 % and 57 %, respectively, suggesting a higher labile carbon content in root exudates. The remaining 36 % of CO2 emissions was derived from the soil and other sources. CO2 emission factors were 6 % for manure compost, 12 % for roots, and 2 % for root exudates. By quantifying the direct emissions from manure compost, residual roots, root exudates, and soil, our study highlights the dominant role of managing root exudates in overall CO2 emissions. These findings can guide targeted carbon reduction strategies, emphasizing the importance of managing root exudates and understanding the relative innocuousness of manure compost applications in the context of CO2 emissions. This novel research quantifies the direct contribution of individual manure compost to CO2 emissions, providing valuable data for carbon cycle models and improving understanding of CO2 contributions from new carbon inputs.

Reducing the mass and decreasing the bioavailability of heavy mental from organic wastes treated by black soldier fly larvae

Black soldier fly larvae (BSFL), Hermetia illucens L., are widely used to reduce the mass of various wastes. However, the potential metal tolerance mechanisms during periods of waste bioconversion by BSFL remain largely unknown. To further reveal the mechanisms, BSFL were used to treat the agricultural organic wastes, including pig manure (PM), cow manure (COM), spent mushroom substrate (SMS), and wet distiller grains (WDG). After these individual and combined waste(s) were treated by BSFL, we investigated the waste reduction rates and evaluated the responses of BSFL gut microbes to heavy metals of agricultural organic wastes. Additionally, the colloidal particles of residual wastes were characterized by combing energy dispersive X-ray (EDX) spectroscopy, Size potential, Zeta potential, and excitation-emission matrix (EEM) spectroscopy. Results indicated that the waste reduction rates were up to 74% in COM+WDG and 69% in WDG, most of heavy metals (e.g., Zn and Co) from organic wastes were not accumulated in the bodies of mature larvae after treatment. Further, results obtained from the prediction of gene function on the basis of 16 S rRNA data revealed that the presence of multi-resistance genes in the gut of BSFL can help the larvae resist Zn and/or Co stress. In addition, the drug sensitivity test implied that BSFL5_L and BSFL6_L from BSFL gut bacterial strains have multi-resistance to Co and Zn. Additionally, EDX results revealed that the colloidal particles in five waste residues after BSFL treatment are mainly consisted of Fe, Ca and Si, which can capture heavy metals (e.g., Cu, Mn). Results from EEM spectroscopy and PARAFAC showed that tryptophan-like and humic-like accumulatively account for 56%- 68% of all components. Importantly, these two components could strongly bind the metal elements and form colloidal particles with high stability, and therefore reduce the heavy metal pollution of agricultural organic wastes. Our findings offered an environment-friendly method to treat agricultural organic wastes, which would be far-reaching influence to our environment.

The improved bioavailability of zein/soybean protein isolate by puerarin in vitro

As the largest emitter of greenhouse gases, the livestock and poultry industry is facing the challenge of increasing production to meet global demand while reducing environmental impacts. Improving feed digestibility by optimizing feed structure (e.g., exogenous additive) is one of the green breeding measures to alleviate carbon pressure. In this study, the interaction mechanism and in vitro digestibility properties of puerarin (PUE) with feed proteins (zein and soy protein isolate (SPI)) to form Zein-PUE and SPI-PUE complexes were investigated mainly by multispectral and molecular docking techniques. Results indicated that the addition of PUE improved the physicochemical properties of proteins (e.g., solubility and disulfide bond contents). Then, the spectral results showed that the binding processes were spontaneous, and the protein structure tended to loose and disordered after binding, and more hydrophobic residues were exposed to the hydrophilic microenvironment. Moreover, on the basis of molecular docking revealed that PUE bound to zein by hydrogen bond, electrostatic and hydrophobic interactions, while with SPI by hydrogen bond and hydrophobic interaction. Finally, in vitro digestion experiments demonstrated that the bioavailability of Zein-PUE and SPI-PUE complexes increased by 1.15 % and 2.11 %, respectively. Overall, PUE is a promising feed additive beneficial for enhancing protein digestibility and bioavailability.

Artificial Humic Substances as Biomimetics of Natural Analogues: Production, Characteristics and Preferences Regarding Their Use

Various processes designed for the humification (HF) of animal husbandry wastes, primarily bird droppings, reduce their volumes, solve environmental problems, and make it possible to obtain products with artificially formed humic substances (HSs) as analogues of natural HSs, usually extracted from fossil sources (coal and peat). This review studies the main characteristics of various biological and physicochemical methods of the HF of animal wastes (composting, anaerobic digestion, pyrolysis, hydrothermal carbonation, acid or alkaline hydrolysis, and subcritical water extraction). A comparative analysis of the HF rates and HS yields in these processes, the characteristics of the resulting artificial HSs (humification index, polymerization index, degree of aromaticity, etc.) was carried out. The main factors (additives, process conditions, waste pretreatment, etc.) that can increase the efficiency of HF and affect the properties of HSs are highlighted. Based on the results of chemical composition analysis, the main trends and preferences with regard to the use of HF products as complex biomimetics are discussed.

Exploring the nitrogen fixing strategy of bacterial communities in nitrogen cycling by adding calcium superphosphate at various periods during composting

Chicken manure, as an organic solid waste with a high nitrogen content, generates large amounts of ammonia during composting, which leads to pollution of the surrounding environment, and causes a reduction in the quality of the compost product. Nitrogen is transformed through the nitrogen cycle and bacterial communities are the main contributors to the transformation of the nitrogen cycle. The microbial composition changes dramatically at different stages during composting. Therefore, calcium superphosphate (SSP) was added to compost as a nitrogen-fixing agent to elucidate the strategy and function of the bacterial community involved in the nitrogen cycle. The results showed that the addition of SSP at the initial, high temperature and cooling stages increased the inorganic nitrogen (NH4+-N, NO3--N) content by 51.99 %, 202.72 % and 173.37 % compared to CK, respectively. In addition, nitrogen cycle functional genes (gdh, nifH, pmoA-amoA, hao, nxrA, nirK, napA, nosZ, narG) abundance were determined by real-time qPCR. The nitrogen cycle genetic results showed that SSP addition at high temperature phase resulted in a 62.43 % down-regulation of ammonification genes, while nitrogen fixation and nitrification genes were enhanced. Random forests revealed a shift in the participation strategy of bacterial communities (e.g., Mycobacterium, Izemoplasmatales, Paracoccus, Ruminococcus) within the nitrogen cycle, leading to altered importance rankings despite involvement in different nitrogen cycle pathways. Moreover, Regression analysis and structural equation modelling revealed that SSP addition at high temperature stage stimulated the bacterial community engaged in nitrogen fixation and nitrification, resulting in increased nitrogen accumulation as NO3--N during composting. This paper offers the potential to yield novel scientific insights into the impact of microbially mediated nitrogen transformation processes and reduce gaseous pollution.

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

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

Identifying the role of array electrodes in improving the compost quality of food waste during electric field-assisted aerobic composting

Low composting temperature and long maturation periods are two major problems during food waste composting. In this study, a novel array-based electric field-assisted aerobic composting (Pin-EAC) process was tested on food waste compost. Pin-EAC increase the composting temperature to 69.3 °C, and improved the germination index by 15%. The Pin-EAC took at least 40% less time to reach the standard compost maturity. The fluorescent spectroscopy results showed that Pin-EAC could increase humic acid and fulvic acid by 33% and 37%, respectively. Pin-EAC could increase the diversity of thermophilic bacteria during composting. The co-occurrence network shown that Pin-EAC are more closely related to oxygen and temperature. This work has initially shown that the use of an electric field could improve food waste composting quality, suggesting that the Pin-EAC process is an effective strategy for high-water and high-oil organic solid waste aerobic composting.

Feedstock optimization with rice husk chicken manure and mature compost during chicken manure composting: Quality and gaseous emissions

This study investigated the impact of mature compost input on compost quality, greenhouse gases (GHGs, i.e. methane and nitrous oxide) and ammonia emissions during chicken manure and rice husk chicken manure co-composting. The experiment used different volumes of mature compost: 10% (T1), 20% (T2), and 30% (T3) to replace rice husk chicken manure. Results showed that mature compost enhanced compost maturity by promoting the activities of Bacillus, Caldicoprobacter, Thermobifida, Pseudogracilibacillus, Brachybacterium, and Sinibacillus. Compared to CK, T1, T2, and T3 reduced NH3 emission by 32.07%, 33.64%, and 56.12%, and mitigated 14.97%, 16.57%, and 26.18% of total nitrogen loss, respectively. Additionally, T2 and T3 reduced CH4 emission by 40.98% and 62.24%, respectively. The N2O emissions were positive correlation with Lactobacillus, Pseudogracilibacillus and ammonium nitrogen (p < 0.05), while T2 reducing total greenhouse effects. Therefore, replacing rice husk chicken manure with 20% mature compost is an efficient and promising approach for composting.

Effect of mulching and biochar addition on the distribution and emission characteristics of N2O from furrow-ridge tillage soils

Mulching and biochar are increasingly used individually in agriculture, but little is known about their combined effects on N2O distribution and dispersion in ridge and furrow profiles. We conducted a 2-year field experiment in northern China to determine soil N2O concentrations using the in situ gas well technique and calculate N2O fluxes from ridge and furrow profiles by the concentration gradient method. The results showed that mulch and biochar increased soil temperature and moisture and altered the mineral nitrogen status, leading to a decrease in the relative abundance of nitrification genes in the furrow area and an increase in the relative abundance of denitrification genes, with denitrification remaining as the main source of N2O production. N2O concentrations in the soil profile increased significantly after fertiliser application, and N2O concentrations in the ridge area of the mulch treatment were much higher than those in the furrow area, where vertical and horizontal diffusion occurred. Biochar addition was effective in reducing N2O concentrations but had no effect on the N2O distribution and diffusion pattern. Soil temperature and moisture, but not soil mineral nitrogen, explained the variation in soil N2O fluxes during the non-fertiliser application period. Compared to furrow-ridge planting (RF), furrow-ridge mulch planting (RFFM), furrow-ridge planting with biochar (RBRF) and furrow-ridge mulch planting with biochar (RFRB) resulted in 9.2%, 11.8% and 20.8% increases in yield per unit area and 1.9%, 26.3% and 27.4% decreases in N2O fluxes per unit of yield, respectively. The interaction between mulching and biochar significantly affected the N2O fluxes per unit of yield. Biochar costs aside, RFRB is very promising for increasing alfalfa yields and reducing N2O fluxes per unit of yield.

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

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

Biochar as functional amendment for antibiotic resistant microbial community survival during hen manure composting

The study aim was to reveal the mechanism of impact of two type biochar on composting of hen manure (HM) and wheat straw (WS). Biochar derived from coconut shell and bamboo used as additives to reduce antibiotic resistant bacteria (ARB) in HM compost. The results manifested that effect of biochar amendment was significant to reduce ARB in HM composting. Compared with control, the microbial activity and abundance were increased in both biochar applied treatment, and bacterial community was changed. Additionally, network analysis revealed that biochar amendment increased the quantity of microorganisms related to organic matter degrading. Among them, coconut shell biochar (CSB) played a pioneering role to mitigate ARB to better exert its effects. Structural correlation analysis showed that CSB reduce ARB mobility and promote organic matter degradation via improving beneficial bacterial community structure. Overall, composting with participation of biochar amendment stimulated antibiotic resistance bacterial dynamics. These results evidence practical value for scientific research and lay the foundation for agricultural promotion of composting.

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

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

The Influence of Poultry Manure-Derived Biochar and Compost on Soil Properties and Plant Biomass Growth

Promising methods for managing poultry manure (PM) include converting poultry manure through pyrolysis to biochar, which can be used for soil applications. The overall goal of this study was to determine the effects of poultry manure-derived biochar and compost on the soil and growth of cherry tomatoes. The biochar obtained at 475 °C was characterized by a relatively high organic matter content of 39.47% and nitrogen content of 3.73%, while it had the lowest C/N ratio of 8.18. According to the recommendations of the EBC, the biochar obtained at 475 °C demonstrated the most beneficial effects in terms of fertilizing potential. The composting of poultry manure with the straw was successful, and the limit of 60 °C was exceeded, which allowed for the hygienization of the compost. The produced compost and biochar are sanitary safe and do not exceed the limits of heavy metal content. The lowest plant biomass was obtained from growing medium A with 3.6 g wet weight (0.24 g dry weight). The measurements of the height of cherry tomatoes showed that growing media D, E, and F allowed the plants to obtain from 602 to 654 mm in height.

Inoculation with thermophiles enhanced the food waste bio-drying and complicated interdomain ecological networks between bacterial and fungal communities

Bio-drying is a practical approach for treating food waste (FW). However, microbial ecological processes during treatment are essential for improving the dry efficiency, and have not been stressed enough. This study analyzed the microbial community succession and two critical periods of interdomain ecological networks (IDENs) during FW bio-drying inoculated with thermophiles (TB), to determine how TB affects FW bio-drying efficiency. The results showed that TB could rapidly colonize in the FW bio-drying, with the highest relative abundance of 5.13%. Inoculating TB increased the maximum temperature, temperature integrated index and moisture removal rate of FW bio-drying (55.7 °C, 219.5 °C, and 86.11% vs. 52.1 °C, 159.1 °C, and 56.02%), thereby accelerating the FW bio-drying efficiency by altering the succession of microbial communities. The structural equation model and IDEN analysis demonstrated that TB inoculation complicated the IDENs between bacterial and fungal communities by significantly and positively affecting bacterial communities (b = 0.39, p < 0.001) and fungal communities (b = 0.32, p < 0.01), thereby enhancing interdomain interactions between bacteria and fungi. Additionally, inoculation TB significantly increased the relative abundance of keystone taxa, including Clostridium sensu stricto, Ochrobactrum, Phenylobacterium, Microvirga and Candida. In conclusion, the inoculation of TB could effectively improve FW bio-drying, which is a promising technology for rapidly reducing FW with high moisture content and recovering resources from it.

From waste to wealth: Innovations in organic solid waste composting

Organic solid waste (OSW) is not only a major source of environmental contamination, but also a vast store of useful materials due to its high concentration of biodegradable components that can be recycled. Composting has been proposed as an effective strategy for recycling OSW back into the soil in light of the necessity of a sustainable and circular economy. In addition, unconventional composting methods such as membrane-covered aerobic composting and vermicomposting have been reported more effective than traditional composting in improving soil biodiversity and promoting plant growth. This review investigates the current advancements and potential trends of using widely available OSW to produce fertilizers. At the same time, this review highlights the crucial role of additives such as microbial agents and biochar in the control of harmful substances in composting. Composting of OSW should include a complete strategy and a methodical way of thinking that can allow product development and decision optimization through interdisciplinary integration and data-driven methodologies. Future research will likely concentrate on the potential in controlling emerging pollutants, evolution of microbial communities, biochemical composition conversion, and the micro properties of different gases and membranes. Additionally, screening of functional bacteria with stable performance and exploration of advanced analytical methods for compost products are important for understanding the intrinsic mechanisms of pollutant degradation.

Comparison of the basic processes of aerobic, anaerobic, and aerobic-anaerobic coupling composting of Chinese medicinal herbal residues

Chinese medicinal herbal residues (CMHRs) are waste generated after extracting Chinese medicinal materials, and they can be used as a renewable bioresource. This study aimed to evaluate the potential of aerobic composting (AC), anaerobic digestion (AD), and aerobic-anaerobic coupling composting (AACC) for the treatment of CMHRs. CMHRs were mixed with sheep manure and biochar, and composted separately under AC, AD, and AACC conditions for 42 days. Physicochemical indices, enzyme activities, and bacterial communities were monitored during composting. Results showed that AACC- and AC-treated CMHRs were well-rotted, with the latter exhibiting the lowest C/N ratio and maximal germination index (GI) values. Higher phosphatase and peroxidase activities were detected during the AACC and AC treatments. Better humification was observed under AACC based on the higher catalase activities and lower E4/E6. AC treatment was effective in reducing compost toxicity. This study provides new insights into biomass resource utilisation.

Hydrothermal carbonization aqueous phase promotes nutrient retention and humic substance formation during aerobic composting of chicken manure

The aqueous phase (AP) of hydrothermal carbonization is rich in humic substances (HSs), which could influence the poultry manure composting process and the product quality. Here, raw AP and its modified product (MAP) with different nitrogen (N) contents were added into chicken manure composting at low (5%) or high (10%) rate. Results showed that all APs addition decreased the temperature and pH but AP-10% increased total N, HSs, and humic acid (HA) of compost by 12%, 18% and 27%, respectively. MAP applications increased the total phosphorus by 8-9% and MAP-10% enhanced the total potussium content by 20%. Additionally, both AP and MAP additions increased the contents of three major components of dissolved organic matter by 20-64%. In conclusion, both AP and MAP can generally improve the chicken manure compost quality, which provides a new idea for the recycling of APs derived from agro-forestry wastes during hydrothermal carbonization.

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

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

Effects of magnesite on nitrogen conversion and bacterial community during pig manure composting

The objective of this research was to elucidate the effect of varying proportions of magnesite (MS) addition - 0% (T1), 2.5% (T2), 5% (T3), 7.5% (T4), and 10% (T5) - on nitrogen transformation and bacterial community dynamics during pig manure composting. In comparison to T1 (control), MS treatments amplified the abundance of Firmicutes, Actinobacteriota, and Halanaerobiaeota, bolstered the metabolic functionality of associated microorganisms, and enhanced the nitrogenous substance metabolic pathway. A complementary effect in core bacillus species played a key role in nitrogen preservation. Compared to T1, 10% MS demonstrated the most substantial influence on composting because Total Kjeldahl Nitrogen increased by 58.31% and NH₃ emission decreased by 41.52%. In conclusion, 10% MS appears to be optimal for pig manure composting, as it can augment microbial abundance and mitigate nitrogen loss. This study offers a more ecologically sound and economically viable method for curtailing nitrogen loss during composting.

The dominant role of cooperation in fungal community drives the humification process of chicken manure composting under addition of regulatory factors

This study aimed to explore the action mechanism of fungal community on the enhancement of humification during chicken manure composting by regulating the core pathway of carbon metabolism - the tricarboxylic acid cycle. Regulators adenosine triphosphate (ATP) and malonic acid were added at the beginning of composting. The analysis of changes in humification parameters showed that the humification degree and stability of compost products were improved by adding regulators. Compared with CK, the humification parameters of adding regulators group increased by 10.98% on average. Meanwhile, adding regulators not only increased key nodes, but also strengthened the positive correlation between fungi, and network relationship was closer. Moreover, core fungi associated with humification parameters were identified by constructing OTU networks, and the division and cooperation mechanism of fungi were confirmed. Ultimately, the functional role of the fungal community acting on humification was confirmed by statistical means, that was, the fungal community promoting humification was the main group of composting process. And the contribution was more obvious in ATP treatment. This study was helpful to gain insight into the mechanism of regulators addition to advance the humification process, and provided new ideas for the safe, efficient and harmless disposal of organic solid waste.

Exploring gaseous emissions and pivotal enzymatic activity during co-composting of branch and pig manure: the effect of particle size of bulking agents

The purpose of current study was to probe the effect of various length of branch on gaseous emissions and vital enzymatic activity. Four lengths (<2 cm, 2 cm, 5 cm, and 10 cm) of clipped branch were mingled with collected pig manure for 100 days aerobic fermentation. The consequence demonstrated that the amendment of 2 cm of branch showed conducive to decline the greenhouse gas emissions, which the CH₄ emissions decreased by 1.62-40.10%, and the N₂O emissions decreased by 21.91-34.04% contrasted with other treatments. Furthermore, the peak degree of enzymatic activities was also observed in 2 cm of branch treatment by the optimizing living condition for microbes. In view of microbiological indicators, the most abundant and complex bacterial community could be monitor in 2 cm of branch composting pile, which verified the microbial facilitation. Summing up, the strategy of 2 cm branch amendment would be recommended.

The effect of calcium superphosphate addition in different stages on the nitrogen fixation and ammonification during chicken manure composting

Nitrogen losses through ammonia (NH₃) emission were an unavoidable issue during chicken manure composting. Calcium superphosphate can be added to effectively limit the emission of NH₃. The results show that adding calcium superphosphate in the heating, high temperature and cooling stages reduces ammonia emission by 18.48 %, 28.19 % and 0.91 % respectively. Furthermore, adding calcium superphosphate at high temperature stage increased the ammonium nitrogen content (NH₄⁺-N), reducing the conversion of organic nitrogen (HON) to NH₄⁺-N. Network analysis indicated that adding calcium superphosphate during the high temperature stage reduced NH₃-related microorganisms and effectively inhibited ammonification. Moreover, the results of qPCR of the ammonification gene gdh and structural equation model (SEM) verify that adding calcium superphosphate at the high temperature stage reduced ammonification and drove ammonification-related bacterial communities to decrease ammonia emissions. Adding superphosphate at high temperature can effectively increase the nitrogen content and reduce gas pollution during composting.

Greenhouse gas emission during swine manure aerobic composting: Insight from the dissolved organic matter associated microbial community succession

Greenhouse gas emissions during aerobic composting is unavoidable, but good practices can minimize emission. Therefore, to explore the key factors influencing the release of greenhouse gas emissions during composting, the inaction of organic matter conversion, greenhouse gas emissions and bacterial community structure during co-composting with different ratio (pig manure and corn straw) over a 6-week period was studied. The excitation-emission matrix fluorescence spectroscopy with the parallel factor was used to identify that dissolved organic matter associated microbial community succession mainly influenced greenhouse gas emissions. Protein-like fractions of dissolved organic matter were more likely to decompose and promote CH₄ and CO₂ emissions, while the humic-like fractions of dissolved organic matter positively affected N₂O emissions. The largest of greenhouse gas emissions was appeared in MR2 with 12.7 kg CO₂-eq, and the MR3 and MR4 reduced greenhouse gas emissions by 26.8 % and 11.4 %, respectively.

Effectiveness of mixing poultry litter compost with rice husk biochar in mitigating ammonia volatilization and carbon dioxide emission

Nitrogen-rich materials such as poultry litter (PL) contributes to substantial N and C loss in the form of ammonia (NH₃) and carbon dioxide (CO₂) during composting. Biochar can act as a sorbent of ammonia (NH₃) and CO₂ emission released during co-composting. Thus, co-composting poultry litter with rice husk biochar as a bulking agent is a good technique to mitigate NH₃ volatilization and CO₂ emission. A study was conducted to evaluate the effects of composting the mixtures of poultry litter with rice husk biochar at different ratios on NH₃ and CO₂ emissions. Four mixtures of poultry litter and rice husk biochar at different rate were composted at 0:1, 0.5:1, 1.3:1 and 2.3:1 ratio of rice husk biochar (RHB): poultry litter (PL) on a dry weight basis to achieve a suitable C/N ratio of 15, 20, 25, and 30, respectively. The results show that composting poultry litter with rice husk biochar can accelerate the breakdown of organic matter, thereby shortening the thermophilic phase compared to composting using poultry litter alone. There was a significant reduction in the cumulative NH₃ emissions, which accounted for 78.38%, 94.60%, and 97.30%, for each C/N ratio of 20, 25, and 30. The total nitrogen (TN) retained relative was 75.96%, 85.61%, 90.24%, and 87.89% for each C/N ratio of 15, 20, 25, and 30 at the completion of composting. Total carbon dioxide lost was 5.64%, 6.62%, 8.91%, and 14.54%, for each C/N ratio of 15, 20, 21, and 30. In addition, the total carbon (TC) retained were 66.60%, 72.56%, 77.39%, and 85.29% for 15, 20, 25, and 30 C/N ratios and shows significant difference as compared with the initial reading of TC of the compost mixtures. In conclusion, mixing and composting rice husk biochar in poultry litter with C/N ratio of 25 helps in reducing the NH₃ volatilization and CO₂ emissions, while reducing the overall operational costs of waste disposal by shortening the composting time alongside nitrogen conservation and carbon sequestration. In formulating the compost mixture with rice husk biochar, the contribution of C and N from the biochar can be neglected in the determination of C/N ratio to predict the rate of mineralization in the compost because biochar has characteristic of being quite inert and recalcitrant in nature.