Improvement of pig manure compost lignocellulose degradation, organic matter humification and compost quality with medical stone

Quinones-enhanced humification in food waste composting: A novel strategy for hazard mitigation and nitrogen retention

The harmless and high-value conversion of organic waste are the core problems to be solved by composting technology. This study introduced an innovative method of promoting targeted humification and nitrogen retention in composting by adding p-benzoquinone (PBQ), the composting without any additives was set as control group (CK). The results indicated that the addition of exogenous quinones led to a 30.1% increase in humic acid (HA) content during the heating and thermophilic phases of composting. Spectroscopic analyses confirmed that exogenous quinones form the core skeleton structure of amino-quinones in HA through composting biochemical reactions. This accelerated the transformation of quinones into recalcitrant HA in the early stages of composting, and reduced CO2 and NH3 by 8% and 78%, respectively. Redundancy analysis (RDA) revealed that the decrease in carbon and nitrogen losses primarily correlated with quinones enhancing HA formation and greater nitrogen incorporation into HA (P < 0.05). Furthermore, the compost treated with quinones demonstrated a decrease in phytotoxicity and earthworm mortality, alongside a significant increase in the relative abundance of actinobacteria, which are associated with the humification process. This research establishes and proposes that co-composting with quinones-containing waste is an effective approach for the sustainable recycling of hazardous solid waste.

Effect of Arbuscular Mycorrhizal Fungi and Rock Phosphate on Growth, Physiology, and Biochemistry of Carob under Water Stress and after Rehydration in Vermicompost-Amended Soil

In the Mediterranean region, reforestation programs record failures following successive drought periods. The use of different plant-growth-promoting amendments and the understanding of drought-induced physiological and biochemical responses of carob will contribute to the reforestation program's success. In this study, the effects of arbuscular-mycorrhizal-fungi (AMF), vermicompost (VC), and rock phosphate (RP) on carob seedlings under drought stress (DS) and recovery (REC) conditions were evaluated. A greenhouse experiment was conducted with carob seedlings grown in the presence of AMF, VC, and RP, applied alone or in combination under well-watered (WW), DS (by stopping irrigation for 12 days), and recovery (REC) conditions. The obtained results indicated that the triple combination (AMF + VC + RP) presented the highest improvement in water potential, photosynthetic pigment content, stomatal conductance, and chlorophyll fluorescence compared to the controls under DS and after REC. In addition, this combination resulted in improved tolerance of carob seedlings to DS and a high potential for rapid recovery after rehydration due to a high accumulation of sugars, proteins, and antioxidant enzymes. In summary, the results underline the importance of inoculating carob with AMF in combination with (in)-organic amendments in improving its tolerance to DS and its recovery performances.

Enhanced humification via lignocellulosic pretreatment in remediation of agricultural solid waste

Stover and manure are the main solid waste in agricultural industry. The generation of stover and manure could lead to serious environmental pollution if not handled properly. Composting is the potential greener solution to remediate and reduce agricultural solid waste, through which stover and manure could be remediated and converted into organic fertilizer, but the long composting period and low efficiency of humic substance production are the key constraints in such remediation approach. In this study, we explore the effect of lignocellulose selective removal on composting by performing chemical pretreatment on agricultural waste followed by utilization of biochar to assist in the remediation by co-composting treatment and reveal the impacts of different lignocellulose component on organic fertilizer production. Aiming to discover the key factors that influence humification during composting process and improve the composting quality as well as comprehensive utilization of agricultural solid waste. The results demonstrated that the removal of selective lignin or hemicellulose led to the shift of abundances lignocellulose-degrading bacteria, which in turn accelerated the degradation of lignocellulose by almost 51.2%. The process also facilitated the remediation of organic waste via humification and increased the humic acid level and HA/FA ratio in just 22 days. The richness of media relies on their lignocellulose content, which is negatively correlated with total nitrogen content, humic acid (HA) content, germination index (GI), and pH, but positively correlated with fulvic acid (FA) and total organic carbon (TOC). The work provides a potential cost effective and efficient framework for agricultural solid waste remediation and reduction.

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

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

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.

The transformation of heavy metal speciation during rapid high-temperature aerobic fermentation of food waste and their potential mechanisms

In this study, the content changes of multiple trace heavy metals (HMs) in food waste using a new rapid high-temperature aerobic fermentation (RTAF) technology and their relationships with different physicochemical factors were researched. The results indicated that the content of HMs in the decomposed products met the industry standards for organic fertilizers (NY/T525-2021, China). Physicochemical factors played an important role in controlling the changes in HM content. The component evolution of dissolved organic matter was studied, and its influences on the transformation of HM speciation showed that the RTAF process converted proteins into humus-like substances. Redundancy analysis revealed that the main factors driving the speciation transformation of HMs were tyrosine-like substances or microbial-derived humus (C3), molecular weight of dissolved organic matter (SUVA254) and humification degree (E250/E365). The increase in humification degree contributed to passivating HMs. The correlation network analysis results showed that the exchangeable HMs (Exc-HMs) were related to Lactobacillus and Pediococcu. Additionally, the cytoskeleton, coenzyme transport and metabolic function of microorganisms affected the Exc-HM content. These research results can provide a scientific basis for the prevention and control of HM pollution during the treatment of food waste.

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.

Regulating pH and Phanerochaete chrysosporium inoculation improved the humification and succession of fungal community at the cooling stage of composting

This study aimed to explore the effect of regulating pH and Phanerochaete chrysosporium inoculation at the cooling stage of composting on the lignocellulose degradation, humification process and related precursors as well as fungal community for secondary fermentation. Results showed that composting with P. chrysosporium inoculation and pH regulation (T4) had 58% cellulose decomposition, 73% lignin degradation and improved enzyme activities for lignin decomposition. There was 81.98% increase of humic substance content and more transformation of polyphenols and amino acids in T4 compared to control. Inoculating P. chrysosporium affected the fungal community diversity, and regulating pH helped to increase the colonization of P. chrysosporium. Network analysis showed that the network complexity and synergy between microorganisms was improved in T4. Correlation and Random Forest analysis suggested that enriched Phanerochaete and Thermomyces in the mature stage of T4 were key taxa for lignocellulose degradation, and humic acid formation by accumulating precursors.

Unraveling the effect of added microbial inoculants on ammonia emissions during co-composting of kitchen waste and sawdust: Core microorganisms and functional genes

Despite the role of microorganisms in nitrogen biotransformation has been extensively explored, how microorganisms mitigate NH₃ emissions in the transformation of nitrogen throughout the composting system is rarely addressed. The present study explored the effect of microbial inoculants (MIs) and the contribution of different composted phases (solid, leachate, and gas) on NH₃ emissions by constructing a co-composting system of kitchen waste and sawdust with and without the addition of MI. The results showed that NH₃ emissions increased markedly after adding MIs, in which the contribution of leachate ammonia volatilization to NH₃ emissions was most prominent. The core microorganisms of NH₃ emission had a clear proliferation owing to the MIs reshaping community stochastic process. Also, MIs can strengthen the co-occurrence between microorganisms and functional genes of nitrogen to promote nitrogen metabolism. In particular, the abundances of nrfA, nrfH, and nirB genes, which could augment the dissimilatory nitrate reduction process, were increased, thus enhancing NH₃ emissions. This study bolsters the fundamental, community-level understanding of nitrogen reduction treatments for agricultural.

Effects of exogenous organic matter addition on agricultural soil microbial communities and relevant enzyme activities in southern China

Soil microbial community composition plays a key role in the decomposition of organic matter, while the quality of exogenous organic matter (EOM: rice straw, roots and pig manure) can influence soil chemical and biological properties. However, the evidences of the effect of combination of crop residues and pig manure on the changes in soil microbial community and enzymes activities are scarce. A greenhouse pot experiment was conducted to investigate the potential effect of EOM by analyzing soil properties, enzyme activities and microbial communities. The experiment consisted of eight treatments: CK (control), S (1% (w/w) rice straw), R (1% (w/w) rice root), SR (1% (w/w) rice straw + 1% (w/w) rice root), and added 1% (w/w) pig manure to CK, S, R and SR, respectively. Results showed that the straw treatment significantly increased the microbial biomass (carbon and nitrogen) and total carbon and nitrogen contents, cellulase and β-1,4-glucosidase activities, bacteria (i.e., gram-positive bacteria and gram-negative bacteria) PLFAs contents relative to CK regardless of whether pig manure was added. Moreover, the interaction between crop residues (e.g., straw and roots) and pig manure significantly influenced the contents of microbial biomass nitrogen and microbial biomass phosphorus, and the ratio of gram-positive bacteria to gram-negative bacteria. Redundance analysis confirmed that pH, nitrate nitrogen, ammonium nitrogen and dissolve organic carbon contents were significantly associated with soil microbial community under crop residues without pig manure addition. Furthermore, the experiment results showed that pig manure application not only provided more abundant nutrients (C, N and P) but also induced higher microbial and enzymatic activity compared with no pig manure addition. Our findings suggest that the combination of above-ground straw and pig manure is a better option for improving the functions of soil ecosystem.

Chemical and microbiological characterization of pig manures and digestates

Livestock and poultry breeding modes, feed compositions and manure collection systems have regional characteristics, which can directly affect the composition of livestock and poultry breeding manure, energy production by anaerobic digestion and resource utilization of products. The chemical, heavy metal contents and microbiological characteristics of pig manures and digestates were characterized in five pig farms and biogas plants in Quzhou (Zhejiang Province) in this study. The results showed that hemicellulose and cellulose of pig manures could be partly degraded in anaerobic digestion, but lignin was difficultly degraded and accumulated in digestates. The content of Zn was highest in the pig manure and digestate samples, followed by Cu, Cr, As, Ni, Pb, Cd, T1 and Hg. The As content was 16.09-31.22 mg kg^-1 in the pig manure and digestate samples, which exceeded the standard limitation requirements in fertilizers in China (≤15 mg kg^-1). Bacteroidota, Firmicutes, Proteobacteria and Spirochaetota dominated in the pig manure and digestate samples, with a relative abundance of 73.6%-99.4%. The microbial community structure in the pig manure samples was quite different among the five farms. The pH, contents of lignin, T1 and As had a significant effect on the microbial community structure in the pig manure samples, while the contents of total phosphorus, NO₃^--N, cellulose and Pb could significantly influence the microbial community structure in the digestate samples. These findings can provide a theoretical basis for recycling manure and improving biogas engineering in large-scale pig farms.

Intermittent aeration to reduce gaseous emission and advance humification in food waste digestate composting: Performance and mechanisms

This study investigated the performance and mechanisms of intermittent aeration to regulate gaseous emission and humification during food waste digestate composting. In addition to continuous aeration, three intermittent aeration regimes were conducted with the on-off interval ratio at 3:1, 2:1, and 1:1 within each 30 min, respectively. Results showed that intermittent aeration regimes reduced gaseous emission and enhanced humification during composting. In particular, intermittent aeration with the on/off ratio of 1:1 was more effective to reduce organic mineralization than other regimes, which alleviated the emission of nitrous oxide and ammonia by 63.1% and 75.7% in comparison with continuous aeration, respectively. In addition, this aeration regime also enhanced the content of humic acid by 24.1%. Further analysis demonstrated that prolonging aeration-off intervals could enrich facultative bacteria (e.g. Atopobium and Clostridium) from digestate and inhibit the proliferation of several aerobic bacteria (e.g. Caldicoprobacter and Marinimicrobium) to retard organic mineralization for humification.

Improving the humification by additives during composting: A review

Humic substances (HSs) are key indicators of compost maturity and are important for the composting process. The application of additives is generally considered to be an efficient and easy-to-master strategy to promote the humification of composting and quickly caught the interest of researchers. This review summarizes the recent literature on humification promotion by additives in the composting process. Firstly, the organic, inorganic, biological, and compound additives are introduced emphatically, and the effects and mechanisms of various additives on composting humification are systematically discussed. Inorganic, organic, biological, and compound additives can promote 5.58-82.19%, 30.61-50.92%, 2.3-40%, and 28.09-104.51% of humification during composting, respectively. Subsequently, the advantages and disadvantages of various additives in promoting composting humification are discussed and indicated that compound additives are the most promising method in promoting composting humification. Finally, future research on humification promotion is also proposed such as long-term stability, environmental impact, and economic feasibility of additive in the large-scale application of composting. It is aiming to provide a reference for future research and the application of additives in composting.

Identification, characteristics and rice growth promotion of a highly efficient cellulolytic bacterial strain, Cellulomonas iranensis ZJW-6, isolated from paddy soil in central China

The microbial degradation of lignocellulose is the best way to treat straw, which has a broad application prospect. It is consistent with the idea of agricultural sustainable development and has an important impact on the utilization of biomass resources. To explore and utilize the microbial resources of lignocellulose degradation, 27 lignocellulose degrading strains were screened from 13 regions in China. ZJW-6 was selected because of its 49.6% lignocellulose weight loss rate. According to the theoretical analysis of the experimental results, the following straw degradation conditions were obtained by ZJW-6: nitrogen source input of 8.45 g/L, a pH of 8.57, and a temperature of 31.63°C, the maximum weight loss rate of rice straw could reach 54.8%. It was concluded that ZJW-6 belonged to Cellulomonas iranensis according to 16S rRNA-encoding gene sequence comparison and identification. ZJW-6 is a Gram-positive bacterium that grows slowly and has a small yellowish green colony. To explain the degradation mechanism of lignocellulose, the experiment of enzymatic properties of the strain was prepared and carried out. It was discovered that ZJW-6 has an excellent ability to degrade cellulose, hemicellulose, and lignin, with cellulose and hemicellulose loss rates reaching almost 50% in 4 days and lignin loss rates reaching nearly 30%. Furthermore, ZJW-6 demonstrated lignocellulose degradation under aerobic and anaerobic conditions, indicating the strain's broad application potential. ZJW-6 was found to be more effective than ordinary humic acid in improving rice soil (available phosphorus, available nitrogen, organic matter) and promoting rice growth in a rice pot experiment (increasing root-shoot ratio, root activity, chlorophyll content and net photosynthetic rate). ZJW-6 plays an important role in promoting the development and utilization of straw resources. It has important significance for the advancement of green agriculture.

Thermophilic-mesophilic biodegradation: An optimized dual-stage biodegradation technique for expeditious stabilization of sewage sludge

The present study investigated the stabilization of fresh sewage sludge through a dual-stage biodegradation process; rotary drum composting in series with vermicomposting. After thermophilic exposure in a rotary drum composter, the partially degraded feedstock was separated into S1 without vermiculture, S2 and S3 with Eudrilus eugeniae and Eisenia fetida vermi-monocultures, respectively. The S3-derived vermicompost exhibited an 80% and 88% reduction in CO₂ and ammonium-nitrogen evolution rates, respectively, demonstrating the expedient stabilization of sludge. The robust, more than 85% seed germination index supported S2 and S3 derived vermicompost viability. A significant decrease in heavy metals was evinced with S2 and S3-derived vermicompost; the S1-derived end product exhibited higher Zn, Cr, and Pb levels in the absence of vermicomposting. Furthermore, soil amended with 20% vermicompost from S3 displayed 50% more plant growth than S1. Thus, the optimized thermophilic-mesophilic dual-biodegradation technique stabilizes sewage sludge quickly, has a lot of potential in sludge management facilities around the world, and produces a marketable end product.

Effects and microbial mechanisms of phosphogypsum and medical stone on organic matter degradation and methane emissions during swine manure composting

The degradation of organic matter (OM) and CH₄ emissions during composting greatly influence the composting efficiency and greenhouse effect. This study evaluated the effects of adding phosphogypsum (PPG) and medical stone (MS) on OM breakdown, CH₄ emissions, and their underlying mechanisms. MS accelerated the breakdown of OM in the early composting stage, whereas PPG increased it in the cooling and maturation periods. At the ending of composting, humification was also significantly promoted by PPG and MS (P < 0.05). Moreover, MS and PPG reduced CH₄ emissions by 27.64% and 23.12%, respectively, and significantly inhibited the activities of methanogens in terms of their abundance (mcrA) and composition (dominant genera such as Methanobrevibacter, Methanocorpusculum, and Methanothermus) (P < 0.05). Interestingly, MS enhanced the activity of enzymes and bacterial metabolism related to OM degradation in the early composting stage, whereas PPG promoted them during the cooling and maturity stages. MS and PPG inhibited the activities of enzymes related to CH₄ release during the cooling and maturity stages. Therefore, PPG and MS may have influenced OM degradation and CH₄ releases during composting via changes in bacterial metabolism and enzyme activity levels. PPG and MS could have altered the activities of methanogens to influence the transformation of carbon and CH₄ emissions according to network analysis and partial least-squares path modeling analysis. These findings provide insights at the molecular level into the effects of adding PPG and MS on OM degradation and CH₄ emissions during composting, thereby facilitating the application of PPG and MS in composting systems.

Succession and change of potential pathogens in the co-composting of rural sewage sludge and food waste

Composting is an effective way to prevent and control the spread of pathogenic microorganisms which could put potential risk to humans and environment, from rural solid waste, especially sewage sludge and food waste. In the study, we aim to analyze the changes of pathogenic bacteria during the co-composting of rural sewage sludge and food waste. The results showed that only 27 pathogenic bacteria were detected after composting, compared to 50 pathogenic bacteria in the raw mixed pile. About 74% of pathogen concentrations dropped below 1000 copies/g after composting. Lactobacillus, Bacillus, Paenibacillus and Comamonas were the core pathogenic bacteria in the compost, of which concentrations were all significantly lower than that in the raw mixed pile at the end of composting. The concentration of Lactobacillus decreased to 3.03 × 10³ copies/g compared to 0 d with 1.25 × 10⁹ copies/g by the end of the composting, while that of Bacillus, Paenibacillus and Comamonas decreased to 2.77 × 10⁴ copies/g, 2.13 × 10⁴ copies/g and 3.38 × 10² copies/g, respectively, with 1.26 × 10⁷ copies/g, 4.71 × 10⁶ copies/g, 1.69 × 10⁸ copies/g on 0 d. Redundancy analysis (RDA) indicated that physicochemical factors and substances could affect the changes of pathogenic bacteria during composting, while temperature was the key influencing factor. In addition, certain potential pathogenic bacteria, such as Bacteroides-Bifidobacterium, show statistically strong and significant co-occurrence during composting, which may increase the risk of multiple infections and also influence their distribution. These findings provide a theoretical reference for biosafety prevention and control in the treatment and disposal of rural solid waste.

Agroindustrial wastes as a substrate for the cultivation of Eruca sativa Miller seedlings: physical-chemical and phytometric parameters assessment

Evaluation was made of the use of organic substrates obtained from the composting of poultry industry wastes, together with crude glycerin, for the production of arugula seedlings (Eruca sativa Miller). The raw materials included hatchery waste, chicken litter, and flotation tank sludge, in combination with other materials such as tree pruning, sugarcane bagasse, crude glycerin (at 0, 1.5, 3.0, 4.5, and 6.0%), and boiler charcoal. Analysis of the organic substrates included determination of nitrogen, phosphorus, and potassium (NPK), pH, electrical conductivity, functional groups, and carboxylic acids. Physical parameters determined were water retention capacity, solids volume, porosity, density, and granulometry. For the arugula seedlings, determinations were made of the ease of removal of the root ball from the tray, the effect of free drop on the root ball, phytometric parameters, and total phenolic compounds. Decreased concentrations of carboxylic acids, together with the presence of aromatic functional groups, indicated maturation/stabilization of the organic substrates. The phytometric measurements indicated that the use of the organic substrates with addition of 3.0, 4.5, and 6.0% of crude glycerin favored arugula production and led to higher contents of total phenolic compounds in the seedlings, with values of 3657.54, 3602.13, and 3232.92 mg GAE g^-1, respectively. The results demonstrated that the use of these organic substrates with the addition of crude glycerin provided satisfactory development of arugula seedlings.

Biodrying of biogas residue through a thermophilic bacterial agent inoculation: Insights into dewatering contribution and microbial mechanism

Biogas residue (BR) is difficult to transport and compost due to its high moisture content. The purpose of this study was to elucidate the dewatering and microbial mechanisms underlying the inoculation of a thermophilic bacterial agent (TBA) onto BR with a high moisture content (i.e., 90.4%). TBA accounted for 78.7% of the water loss rate in BR, dramatically higher than the effects of aeration, external heat, or indigenous microorganisms (i.e., 1.8%, 0.1%, and 19.4%, respectively). Furthermore, TBA inoculation resulted in a stable product [with a low moisture content (9.4%) and a high seed germination index (107.3%)]. Finally, TBA increased microbial diversity and the abundance of functional bacteria (Proteobacteria and Bacteroidota), which might be beneficial for refractory organic compound decomposition and plant growth. Thus, biodrying BR via inoculation with a TBA is recommended economically.

Bio-Enhanced Degradation Strategies for Fluoroquinolones in the Sewage Sludge Composting Stage: Molecular Modification and Resistance Gene Regulation

The molecular/protein–protein docking and the index normalization method assisted by the entropy weight method were used to quantitatively evaluate the biodegradability of fluoroquinolones (FQs) under different biodegradation systems. Four biodegradability three-dimensional quantitative structure–activity relationship (3D-QSAR) models of FQs were constructed to design FQ derivatives with improved biodegradability. Through the evaluation of the environmental friendliness and functional properties, the FQ derivatives with high biodegradability, improved functionality, and environmental friendliness were screened. Moreover, four bio-enhanced degradation scenarios of FQs were set up according to the different temperatures and carbon–nitrogen ratio (C/N) in the sewage sludge composting stage, and the molecular dynamic (MD) simulation assisted by protein–protein docking was used to screen the external environmental factors that promote the degradation of FQs by thermophilic bacteria or group under different scenarios. Finally, MD simulation assisted by sampling method was used to validate and screen the application scheme of field measures to enhance the expression of antibacterial resistance of FQ derivatives in an agricultural soil environment after activated sludge land use. This study aims to provide theoretical support for the development of highly biodegradable FQ derivatives and the mitigation of potential risks that FQs may pose to the environment and humans through the food chain.

Humic Substances Derived From Biomass Waste During Aerobic Composting and Hydrothermal Treatment: A Review

Humic substances (HSs) occupy 80% of organic matter in soil and have been widely applied for soil remediation agents, potential battery materials, and adsorbents. Since the HS extraction rate is very low by microbial degradation in nature, artificial humification processes such as aerobic composting (AC) and hydrothermal treatment (HT) have attracted a great deal of attention as the most important strategies in HS production. This article aims to provide a state-of-the-art review on the development of conversion of biomass waste into HSs based on AC and HT for the first time in terms of mechanisms, characteristics of HSs’ molecular structure, and influencing factors. In addition, some differences based on the aforementioned information between AC and HT are reviewed and discussed in the conversion of biomass waste into HSs in a pioneering way. For biomass waste conversion, a feasible strategy on effective humification processes by combining AC with HT is proposed.

Evaluation of the applicability of organic amendments from microbially driven carbon and nitrogen transformations

Pig manure (PM), wheat straw (WS), compost product (CP) and improved compost product (IC) are very important agricultural organic resources. In this study, their applicability as soil organic fertilizations (OFs) in terms of their properties and influence on soil properties through an incubation experiment and a field verification were evaluated. The property differences indicated that wheat straw has the highest C/N ratio, and compost products contain more aromatic compounds compared with pig manure and wheat straw. The results of incubation experiment showed that OFs promoted the carbon and nitrogen transformation driven by related microorganisms and their functional metabolisms. The PM treatment had the highest proportion of Labile organic carbon to soil organic carbon (LOC/SOC) and ratio of dissolved organic carbon to soil organic carbon (DOC/SOC), while WS treatment had the lowest values. The highest net N mineralization rate and nitrification rate was observed in the WS treatment, but the lowest amounts were under the PM treatment. Additionally, the similar findings were also obtained from the field examination. Therefore, compost products were more applicable in agricultural soil as OF insight from changes in carbon, nitrogen and microbial community. Furthermore, the result of UV-vision showed that the largest amount of aromatic structure was observed in IC relative to CP. It can be concluded that CP was more conducive to fix carbon and provide available nitrogen for crops among four OFs.

Mechanism that allows manno-oligosaccharide to promote cellulose degradation by the bacterial community and the composting of cow manure with straw

The new sugar source manno-oligosaccharide can regulate the structure of the microbial community. This study investigated the effects of adding manno-oligosaccharide at four different levels (0, 0.1%, 0.5%, and 1% w/w compost) to composting cow manure and straw on lignocellulose degradation and the bacterial community. Adding 0.5% manno-oligosaccharide had the greatest effects on accelerating the composting process, reducing its toxicity, and improving the stability of the product. After composting for 25 days, adding 0.5% manno-oligosaccharide decreased the hemicellulose, cellulose, and lignin contents to 2.25%, 11.25%, and 7.07%, respectively, compared with those under CK. Manno-oligosaccharide promoted the degradation of lignocellulose by increasing the abundances of Thermobifida, Streptomyces, and Luteimonas. In addition, manno-oligosaccharide inhibited pathogenic bacteria and increased the abundances of functional genes related to metabolism. Finally, adding 0.5% manno-oligosaccharide mainly affected the degradation of lignocellulose by enhancing the C/N ratio and the abundances of Streptomyces and the secretion system during composting according to redundancy analysis.

Optimising mixed aerobic and anaerobic composting process parameters for reducing bacterial pathogenicity in compost-derived products

Although composting techniques are continuously optimised and adjusted, the removal of bacterial pathogen based on the quality of composting products needs further to ensure safe of agricultural use. In this study, we combined aerobic composting and anaerobic process to determine the optimal combination (turning frequency of once a day, the proportion of swine manure to corn straw (3:1), and mixed 6-day anaerobic process) that benefits the reduction of bacterial pathogens, among which the maximum removal efficiency of up to 92.96% was observed for Clostridium_sensu_stricto_1 reached, thereby improving the quality of the compost products. The variation partition analysis and redundancy analysis indicated that physicochemical factors such as temperature, TOC, and pH significantly affected the removal of bacterial pathogens. Therefore, the additive effects of physicochemical factors on bacterial pathogen removal requires further process optimisation. These findings offer powerful technological support for improving agricultural waste recycling and enhancing the safety of fertiliser application.

Process optimization by combining in-vessel composting and vermicomposting of vegetable waste

The process parameters of in-vessel rotary drum composting (RDC) with vermicomposting (VC) were investigated for the conversion of vegetable waste into vermicompost. After 7-day initial thermophilic exposure (maximal 51.5 °C in 24 h), the partially degraded RDC waste was divided into R1 (no vermiculture), R2, R3, and R4 (with Eudrilus eugeniae; Eisenia fetida; and Perionyx excavates monocultures, respectively). R3 derived vermicompost displayed maximum optimal process parameters and desirable compost qualities. Against the constant 2.2% nitrogen content of R1, an increase from 1.4 to 4.15% was seen in R3, with a 52.5% reduction in total organic carbon (TOC). A clear testimony to the enhanced nutritional content and fitness of the novel combination of RDC thermophilic biodegradation and E. fetida based vermicomposting. In an environmentally compatible mode, the faster organic deconstruction in 27 days could substantially alter organic waste treatment in the immediate future.

Response of bacterial community to iron oxide nanoparticles during agricultural waste composting and driving factors analysis

The succession of bacterial communities and their function, and the core microorganisms for water soluble organic carbon (WSC) and organic matter (OM) changes during agricultural waste composting with addition of iron oxide nanomaterials (FeONPs, Fe₂O₃ NPs and Fe₃O₄ NPs) were investigated. Moreover, driving factors for bacterial composition and metabolism were analyzed. Results showed that FeONPs treatments increased the relative abundance of thermophilic microorganisms for OM degradation. Most of the core genera were responsible for decomposition of OM and synthesis of WSC. Additionally, FeONPs promoted the metabolism of amino acids. The most significant factors for dominant genera in control, Fe₂O₃ NPs and Fe₃O₄ NPs group were moisture (62.1%), moisture (62.0%) and OM (58.2%), respectively. For metabolism, the most significant factors in control, Fe₂O₃ NPs and Fe₃O₄ NPs group were temperature (57.2%), NO₃^--N (60.5%), NO₃^--N (62.6%), respectively. The relationships between compost properties, bacterial community and metabolism were changed by FeONPs.

Effects of microplastics on humification and fungal community during cow manure composting

The effect of microplastics (MPs) on the biological treatment of organic waste has been extensively studied, but little is known about the influence of different MPs on composting humification and the fungal community. In this study, PE, PVC, and PHA MPs were individually mixed with cow dung and sawdust and then composted. The results showed that different MPs had various influences on humification, and the humic acid to fulvic acid ratio of all MP-added treatments (0.44-0.83) was lower than that of the control (0.91). During the composting process, Ascomycota (26.32-89.14%) and Basidiomycota (0.47-4.78%) are the dominant phyla in all treatments and all microplastics decreased the diversity and richness of the fungal community at the thermophilic stage of composting. Exposure to MPs had an obvious effect on the fungal community at the genus level, and the addition of PHA and PE MPs increased the relative abundance of phytopathogenic fungi. LEfSe and network analysis indicated that MPs reduced the number of biomarkers and led to a simpler and more unstable fungal community structure compared to the control. This study has important implications for assessing microplastic pollution and organic waste disposal.

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.

Insight into the effects of regulating denitrification on composting: Strategies to simultaneously reduce environmental pollution risk and promote aromatic humic substance formation

Denitrification during composting is a hidden danger that causes environmental pollution risk and aromatic humic substance damage, which needs to be better regulate urgently. In this study, two denitrification regulation methods, moisture and biochar amendment, were conducted during chicken manure composting. Denitrification performance data showed two regulation methods obviously reduced NO₃^--N, NO₂^--N and N₂ contents. Humic substance increased by 25.3 % and 29.1 % under two regulations. Microbiological analysis indicated that two regulation methods could decreasing denitrifying functional microbes with aroma degradation capability. Subsequently, denitrification gene narG, nirS, nosZ were significantly inhibited (p < 0.05) and the aromatic degradation metabolism pathways were down-regulated. Correlation analysis further revealed the important influence of interspecific interactions and non-biological characteristics on functional microbes. These results provided important scientific basis to denitrification regulation in the practice of composting, which achieved the purpose of simultaneously controlling environmental pollution risk and conducing end-product formation.

Nitrate shifted microenvironment: Driven aromatic-ring cleavage microbes and aromatic compounds precursor biodegradation during sludge composting

The aim of this study was to clarify the aromatic cleavage pathways and microbes involved in the adverse effect of nitrate on aromatic compounds humic substances during sludge composting. Results showed that the functional microbes involved in aromatic compounds humic substances precursors (catechol, tyrosine, tryptophan and phenylalanine) cleavage pathways significantly enriched after nitrate addition. Linear regression analysis showed that aromatic-ring cleavage functional microbes exhibited significant negative correlation with aromatic humic substances (p < 0.05). Furthermore, network analysis indicated that most of microbial communities prefer cooperative with aromatic-ring cleavage functional microbes. Structural equation model further revealed that composting microenvironment drove aromatic-ring cleavage functional microbes activities, resulting in the biodegradation of complex aromatic compounds. This study parsed the effect of a negative factor on aromatic compounds humic substances from an opposing perspective. Properly controlling nitrate concentration and aromatic-ring cleavage functional microbes involved in precursors cleavage was suggested to the practice of composting.

Illite/smectite clay regulating laccase encoded genes to boost lignin decomposition and humus formation in composting habitats revealed by metagenomics analysis

The aim of this study was to use metagenomics to investigate how Illite/smectite clay (I/S) affected Auxiliary Activities (AA1, AA2, AA3) thereby enhancing lignin decomposition and humification. Metagenomics analysis illustrated that the abundances of AA1, AA2, AA3 in test group (TG) with 10% I/S were 28.98%, 15.18%, 14.36% higher than that in reference group (RG), respectively. Meanwhile, I/S greatly boosted the efficiency of lignin degradation (17.96%) and humus formation (7.16%) compared with RG (13.10%, 3.49%). Furthermore, Actinobacteria was the microorganism with the greatest contribution in RG and TG to secreting AA1 (41.12%, 57.37%), AA2 (62.42%, 65.28%), AA3 (47.04%, 55.47%). Redundancy analysis (RDA) demonstrated that I/S could make the laccase encoding gene-AA1 contribute more to HS formation relative to AA2 and AA3. In conclusion, applying I/S in cattle manure composting effectively improved the abundance, bioavailability of lignin degradation functional gene enzymes and the composting efficiency.

Increased enzyme activities and fungal degraders by Gloeophyllum trabeum inoculation improve lignocellulose degradation efficiency during manure-straw composting

The present study investigated the effect of brown-rot fungus Gloeophyllum trabeum inoculation on lignocellulose degradation, enzyme activities and fungal community during co-composting of swine manure and wheat straw. G. trabeum inoculation shortened the maturation period of composting from 39 to 30 days. Composting piles inoculated with G. trabeum showed a higher degree of maturity as indicated by 31.6% lower C/N ratio and 29.4% higher GI. The decomposition rate of cellulose, hemicellulose and lignin was increased by 181.1%, 49.4% and 109.4%, respectively, due to higher activities of filter paper enzyme, xylanase, manganese peroxidase and laccase. Redundancy analysis showed that inoculating G. trabeum influenced the succession of fungal communities by changing the main physicochemical parameters, resulting in the increased relative abundance of Aspergillus, Mycothermus and Melanocarpus. Pearson correlation analysis indicated that more dominant fungal genera were involved in the production of lignocellulose-degrading enzymes after G. trabeum inoculation.

Hydrogen peroxide plus ascorbic acid enhanced organic matter deconstructions and composting performances via changing microbial communities

This work aims to investigate the influence of hydrogen peroxide (H₂O₂) and ascorbic acid (ASCA) on the physicochemical characteristics, organic matter (OM) deconstructions, humification degree and succession of bacterial communities for co-composting of bagasse pith and dairy manure. The results indicated that H₂O₂ and ASCA accelerated the degradation of lignocellulose, improved the transformation of dissolved organic matter (DOM), and enhanced the content of humic substance (HS) and the degree of its aromatization. The bacterial communities were significantly changed in the presence of additives, in which the relative abundances of Firmicutes and Actinobacteria significantly increased. Redundancy analysis (RDA) indicated that the degradation of OM and lignocellulose more influenced the bacterial community compositions. Conclusively, adding H₂O₂ and ASCA accelerated lignocellulose degradation efficiency, and improved the composting process, which provided an optimized method to dispose of lignocellulose wastes and livestock manure.

The effects of biochar/compost for adsorption behaviors of sulfamethoxazole in amended wetland soil

Biochar and compost were two common amendments for the polluted soil. However, few studies were conducted to study the sorption of organic pollutants on combined biochar-compost and the relative adsorption mechanisms in mixed soil. The work had studied the adsorption and desorption behaviors of sulfamethoxazole (SMX) onto wetland soil after amended with biochar and/or compost. Moreover, the physicochemical and morphology properties of biochar/compost and amended soils were analyzed to discuss the relative adsorption mechanisms. Studies showed that the adsorption capacity of amended soils increased with the total amount of biochar or/and compost added, which was positively related to SOM, CEC, and EC of amended soils, but had nothing to do with the type of additives. Compared with the compost-treated treatments, the biochar-treated treatments generally achieved lower desorption rates, which also had demonstrated both different adsorption mechanisms. Pore filling and hydrophobic partitioning were the main adsorption mechanisms for biochar and compost, respectively. Though biochar owned developed pore structure, however, pore-filling of biochar was overwhelmingly weakened due to pore-blocking in mixed soils. Hence, in soil environment, compost is a kind of a more desirable amendment than biochar in absorbing and degrading organic pollutants.

Current status of global warming potential reduction by cleaner composting

The global living standards are currently undergoing a stage of growth; however, such improvement also brings some challenges. Global warming is the greatest threat to all living things and attracts more and more attention on a global scale due to the rapid development of economy. Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are the common components of greenhouse gases, which contribute to the global warming. Mitigation technologies for these gas emissions are urgently needed in every industry for the aim of cleaner production. Traditional agriculture also contributes significantly to enhance the greenhouse gases emission. Composting is a novel and economic greenhouse gases mitigation strategy compared to other technologies in terms of the organic waste disposal. Some of the European countries showed an increase of more than 50% in the composting rate. The microbial respiration, nitrification and denitrification processes, and the generation of anaerobic condition makes the emission of greenhouse gases inevitable during composting. However, although there have been a lot of papers that focused on the reduction of greenhouse gases emission in composting, none of these has summarized the methods of reducing the emission of greenhouse gases during the composting. This review discusses the benefit of composting in greenhouse gases mitigation in the organic waste management and the current methods to improve mitigation efficiency during cleaner composting. Key physical, chemical, and biological parameters related to greenhouse gases mitigation strategies were precisely studied to give a deep understanding about the emission of greenhouse gases during cleaner composting. Furthermore, the mechanism of greenhouse gases emission mitigation strategies for cleaner composting based on various external measures would be helpful for the exploration of novel and effective mitigation strategies.

Citrus Segment Degradation Potential, Enzyme Safety Evaluation, and Whole Genome Sequence of Aspergillus aculeatus Strain ZC-1005

Aspergillus aculeatus ZC-1005 (ZC-1005 was used as the abbreviation of this strain) is a hemicellulase-producing strain isolated from rotten citrus rind buried in the soil. Our previous study has shown its biochemical properties including high xylanase activity, mannanase activity, and degradation reaction with citrus mesocarp. In this study, we focused more on the enzyme safety evaluation and the genome sequencing via PacBio and Illumina platforms. High biological safety of the crude enzymes of ZC-1005 has been proven by the acute oral toxicity test, sub-chronic toxicity test, micronucleus test, and sperm malformation test. The genome of ZC-1005 had a GC content of 52.53%, with a size of 35,458,484 bp, and encoded 10,147 genes. Strain ZC-1005 harbored 269 glycosyl hydrolase (GH) genes of 64 families. The fungus produces cellulose-acting (GH3, GH5, GH12, and GH1) and hemicellulose-acting enzymes (GH16, GH31, GH2, and GH92). In genome annotation, we paid more attention to the genes encoding xylanase, such as gene 01512, gene 05833, gene 05469, gene 07781, gene 08432, gene 09042, gene 08008, and gene 09694. The collaboration between complete genome information and the degradation test confirmed that ZC-1005 could degrade cellulose and xylan. Our results showed that the citrus enzymatic decapsulation technology was efficacious and safe for canned citrus product processing, which may also solve the industrial waste problem. Therefore, ZC-1005 and the crude enzyme secreted from the strain were very promising to be used in the citrus processing industry.

Additive grain-size: An innovative perspective to investigate the transformation among heavy metal and phosphorus fractions during aerobic composting

Considerable researches have been devoted to ascertain the transformation among heavy metal (HM) or phosphorus (P) fractions during aerobic composting. However, available information that additives with different grain-sizes regulate the activation mechanism on P through influencing the passivation effect on HMs remains limited. Thus, this work aimed to investigate the dynamic changes in HM-fractions and P-fractions, and ascertain the interaction pathway between HMs and P during aerobic composting amended with medical stone (Coarse medical stone, 3-5 mm; Fine medical stone, < 0.1 mm). Medical stone, especially for coarse-grained medical stone, significantly enhanced the HM-passivation and P-activation during the composting (P < 0.05). The bioavailability factor of HMs decreased by 48.05% (Cu), 20.65% (Pb), 15.58% (Cd) and 6.10% (Zn), and the content of labile available P (LAP) increased by 6.45%. HMs, with the explanatory capacity of 65.9%-84.9%, was important parameter superior to temperature (0.8%-5.4%), moisture content (MC, 0.1%-1.7%), pH (0.1%-8.7%), electric conductivity (EC, 0.8%-9.8%), carbon-to-nitrogen (C:N, 0.3%-2.3%) ratio and dissolved organic carbon (DOC, 0.4%-3.1%), to evaluate the transformation among P-fractions. Our results cast a new light on P-activation with respect to HM-passivation during aerobic composting.

Elucidating the optimum added dosage of Diatomite during co-composting of pig manure and sawdust: Carbon dynamics and microbial community

Six dosages of DM (0%, 2.5%, 5.0%, 10%, 15% and 20%) were added into initial mixtures for 42 days of aerobic composting to investigate the optimum added dosage of Diatomite (DM) during co-composting of pig manure and sawdust. The results showed that adding DM was beneficial for reducing CH₄ emissions and greenhouse gas emission equivalent (GHGE) values by 15.63-24.25% and 14.33-69.08%, respectively. Meanwhile, the main contributor to the GHGE value was N₂O (58.76-75.98%), followed by CH₄ (17.22-29.16%) and NH₃ (6.38-13.36%). Moreover, the maximum values in the degradation of total organic matter and the formation rate of humic acid were 20.46% and 82.19% in 10% DM added treatment (T3), respectively. Furthermore, the increase in spectral parameters, including the specific UV absorbance at 254 nm (SUVA₂₅₄), the specific UV absorbance at 280 nm (SUVA₂₈₀) and Fourier transform - infrared parameters were facilitated by DM amendment. Additionally, the higher values of the relative abundances of Proteobacteria (50.98%) and Bacteroidetes (12.73%), and related metabolisms such as carbohydrate metabolism and amino acid metabolism, as well as the lower value of methane metabolism reported in T3, supported the difference in CH₄ and humification of the two treatments. In conclusion, DM was determined to be an eco-practical additive to improve the quality of end products and reduce potential risks, and the best treatment in this study was 10% added treatment based on dry weight.

Manipulation of composting oxygen supply to facilitate dissolved organic matter (DOM) accumulation which can enhance maize growth

Promotion of crop yield by compost application is generally thought to be ascribed to a better supply of macro and micronutrients, however the importance of compost DOM on plant growth has not been well demonstrated. In this study, composting of chicken manure, spent mushroom and sawdust was conducted under aerobic or anaerobic condition to determine the effects of compost DOM on plant growth. It was found that dissolved organic matter (DOM) first increased and then decreased in compost, and DOM of anaerobic compost was slightly higher than that of aerobic compost. When compost extract was applied to maize, among N, P, K and DOM content, it was DOM content that was most significantly and strongly related to plant biomass (r = 0.843, p＜0.001). Compost DOM was also strongly related to soil properties, the improvement of which can also promote plant growth. Compost application confirmed that higher compost DOM results in greater plant biomass. In order to facilitate compost DOM accumulation, we designed a novel composting process which combined aerobic and anaerobic treatments, and the resulting compost (A-Ana compost) with the highest amount of DOM displayed the best performance in promotion of plant growth. A-Ana compost was able to increase maize biomass by 32.71% and 12.40% compared with only anaerobic or aerobic compost, respectively. Therefore, DOM is a critical factor determining compost quality and it is feasible to manipulate composting oxygen supply condition to increase compost DOM, which will lead to increased plant yield.

The influences of illite/smectite clay on lignocellulose decomposition and maturation process revealed by metagenomics analysis during cattle manure composting

The purpose of this study was to analyze the effects of illite/smectite clay (I/S) on lignocellulosic degradation and humification process via metagenomics analysis during cattle manure composting. The test group (TG) with 10% I/S and the reference group (RG) were established. The results indicated that the addition of I/S made the degradation rate of cellulose, hemicellulose and lignin in TG (1.56%, 29.01%, 19.95%) was higher than that in RG (1.16%, 17.24%, 13.14%). Compared with RG, the abundance values of AA2, AA10, GH1 and GH10 in TG increased by 15.18%, 29.28%, 31.08%, 21.65%, respectively. Meanwhile, humic substance (HS) content was increased by 3.49% and 7.16% during RG and TG composting. Furthermore, the microbial community in TG changed, in which the relative abundance of Actinobacteria increased and Proteobacteria decreased. Redundancy analysis (RDA) showed that the temperature was positively correlated with the abundance of AA2, AA10, GH1 and GH10, whereas the organic matter content was negatively correlated. Overall, adding I/S to the composting could stimulate microbial activity, promote the degradation of lignocellulose and humification process.

Consumers’ and Farmers’ Perceptions in Europe Regarding the Use of Composted Bedding Material from Cattle

By-products like sawdust and straw are applied in compost bedded-pack barns (CBP) for cattle. These materials, which are gradually mixed with excreta and undergo a composting process, serve as a lying bed for the cattle. This study aims to assess the perception of consumers and farmers regarding the use of CBP during the grazing season of cattle for raising other animals or for growing food crops. This was examined by combining surveys with consumers from eight European countries and cattle farmers, focus groups with consumers, and in-depth interviews with individual farmers who implemented alternative uses of compost. The results showed that farmers preferred the compost bedded-pack system to the cubicle system in terms of sustainability and market aspects, although the cost of the bedding material required for CBP was seen as a significant negative aspect. Around half of all consumers indicated that the compost can be used for non-edible products and 26% indicated the compost can be used for raising other animals. Furthermore, 5% of consumers felt that compost should not be used for any other purpose. There were statistically significant differences between countries; therefore, regional specificities should be taken into account when marketing products from compost in CBP barns.

Microbial degradation in the co-composting of pig manure and biogas residue using a recyclable cement-based synthetic amendment

This research investigated a synthetic amendment to improve composting and resource recycling of pig manure and biogas residue. We further examined whether adding a synthetic amendment impacts the microbial ecosystem in the composted materials. Three mixing ratios were used to investigate composting performance: no synthetic amendment (T0), 5% synthetic amendment (T1), and 10% synthetic amendment (T2) (T1 and T2 were measured as a wet weight ratio). There were no significant differences in the fundamental characteristics between composting products in T0 and T1. The moisture content of composting material in T0, T1, and T2 significantly decreased from a baseline of approximately 65% to 35.5%, 37.3%, and 55.9%, respectively. Meanwhile, the germination index significantly increased to 111.6%, 155.6%, and 62.3%, respectively. When an optimal proportion of synthetic amendment was added, T1 showed high degree of humification, lignocellulase activities, and effective biodegradation. Firmicutes, Actinobacteria, Proteobacteria, and Bacteroidetes were the dominant bacteria, while Ascomycota and Basidiomycota were the dominant fungi in all treatment groups. Amino sugar and nucleotide sugar metabolism, glycolysis, starch, and sucrose metabolism were among the primary pathways in predicted functions. The synthetic amendment can generate a mature composting product and can be reused or recycled to conserve resources.

Does biochar inhibit the bioavailability and bioaccumulation of As and Cd in co-contaminated soils? A meta-analysis

Biochar, an effective and low-cost amendment for immobilizing heavy metals, has been extensively studied. However, the simultaneous inhibition effects of biochar on the plant uptake for arsenic (As) and cadmium (Cd) in co-contaminated soils are still ambiguous due to their distinct environmental behaviors. A meta-analysis was conducted to quantitatively assess the effects using 1030 individual observations from 52 articles. On average, biochar application significantly decreased the bioavailability of Cd in soils by 50.12%, while slightly increased the bioavailability of As in soils by 2.39%. The more instructive result is that biochar application could also simultaneously reduce the concentration of As and Cd in plants by 25.48% and 38.66%, respectively. The orders of the decreased percentage of As and Cd in various tissues were root < stem< leaf < grain, and root < leaf < stem < grain, respectively. According to the analysis of critical factors, manure biochar, low pyrolysis temperature (at <400 °C), low application rate (<2%), and high SOC (>30 g/kg) were more conducive to reduce the bioaccumulation of As and Cd simultaneously in co-contaminated soils. Pristine and modified biochar could inhibit As and Cd accumulation in crops, but their efficiencies need to be further improved to ensure the safety of crop productions. Overall, the meta-analysis suggests that biochar has the potential to remedy the As and Cd co-contaminated soils.

Effects of phosphogypsum and medical stone on nitrogen transformation, nitrogen functional genes, and bacterial community during aerobic composting

This study explored the effects of adding phosphogypsum (PPG), medical stone (MS), and both (PPM) during composting on nitrogen transformation, nitrogen functional genes, the bacterial community, and their relationships with NH₃ and N₂O emissions. Adding MS and PPM reduced NH₃ emissions by 25.78-68.37% and N₂O emissions by 19.00-42.86%. PPG reduced NH₃ emissions by 59.74% but slightly increased N₂O emissions by 8.15%. MS was strongly correlated with the amoA-dominated nitrification process. PPG and PPM had strong correlations with nirS- and nirK-dominated, and nosZ-dominated denitrification processes, respectively. PPM promoted nitrification and denitrification processes more than PPG and MS. Different functional bacteria had key roles in nitrification and denitrification during different composting stages. Firmicutes probably contributed to the conversion and release of nitrogen in the thermophilic period, whereas Proteobacteria, Chloroflexi, Bacteroidetes, and other phyla might have played important roles in the cooling and maturation periods. PPM obtained the greatest reductions in NH₃ and N₂O release via the regulation of environmental variables, nitrogen functional genes, and the bacterial community. Overall, these results provide insights at a molecular level into the effects of PPG and MS on nitrogen transformation and NH₃ and N₂O emissions during composting.

Effect of clay on greenhouse gas emissions and humification during pig manure composting as supported by spectroscopic evidence

To evaluate the effect of clay on greenhouse gas (GHGs) emissions and humification during pig manure (PM) composting, two lab-scale composting experiments, a control and a 10% clay treatment, were established. The results showed that adding clay reduced the emissions of CH₄ and N₂O by 45.88% and 86.79%, respectively, promoted the degradation of organic matter (OM) and facilitated the synthesis of humic acid (HA). The spectrum of dissolved organic matter (DOM) indicated that adding clay promoted the formation of aromatic carbon compounds and the degradation of aliphatic carbon. Furthermore, compared with the control, the spectral parameters including the specific UV absorbance at 254 nm (SUVA₂₅₄), the specific UV absorbance at 280 nm (SUVA₂₈₀) and the ration of the area at 435-480 nm and at 300-345 nm (A₄/A₁) of DOM were increased by 5.45%, 3.66% and 29.26%, respectively. Combined with the excitation - emission matrix (EEM) and the percentage fluorescence response (Pi,n), the clay amendment promoted the decomposition of tyrosine and Tryptophan and the formation of humic-like substances, and thus increased humification. The variation in the HA/fulvic acid and the humification index confirmed these results. Therefore, clay amendment is beneficial for reducing GHG emissions, promoting humification and aromatization during pig manure composting.

Effects of carbon-based additives and ventilation rate on nitrogen loss and microbial community during chicken manure composting

Aerobic composting is a sustainable method for chicken manure recycling, while its unsuitable porosity and carbon to nitrogen ratio (C/N) may result in high nitrogen loss and incomplete composting. With the aim to investigate the effects of carbon-based additives and two ventilation rates on chicken manure composting and microbial community, two series of treatments were set up for chicken manure composting, in order to investigate their effects on the biodegradation process, ammonia (NH₃) emission, nitrogen loss, physiochemical properties and microbial community. The results showed that additives and ventilation rates set in the current study influenced the carbon dioxide (CO₂) production from the 2^nd week and also the physiochemical parameters during the entire process, while no inhibitory effect on the maturity were observed. With woody peat as additive, the NH₃ emission amount and nitrogen loss rate were shown as 15.86 mg and 4.02%, less than those in other treatments, 31.08–80.13 mg and 24.26–34.24%, respectively. The high aeration rate increased the NH₃ emission and nitrogen loss, which were varied when the additives were different. The terminal restriction fragment length polymorphism (T-RFLP) results showed that the additives and the ventilation rates changed the microbial community, while the prominent microbial clones belonged to the class of Bacilli and Clostridia (in the phylum of Firmicutes), and Alphaproteobacteria, Deltaproteobacteria and Gammaproteobacteria (in the phylum of Proteobacteria). Bacillus spp. was observed to be the most dominant bacteria in all the composting stages and treatments. It was concluded that woody peat could improve chicken manure composting more than other additives, especially on reducing nitrogen loss, meanwhile 0.18 L‧min^-1‧kg^-1 DM was suitable for various additives. Therefore, suitable additive and aeration rate could be used in practical application, which could significantly reduce nitrogen loss without influence on the compos maturity process.

Stabilization of heavy metal-contaminated soils by biochar: Challenges and recommendations

Various types of biochar have been widely used to remediate soil contamination from heavy metals (HMs) and to reduce HM mobility and bioavailability in soils in recent years. Most researchers have paid attention to the beneficial effects of biochar during the remediation process, but few have emphasized their negative effects and the challenges for their application. In this review, the negative effects and challenges of applying biochar for the remediation of HM-contaminated soils are thoroughly summarized and discussed, including the changeable characteristics of biochar, biochar over-application, toxic substances in biochar, activation of some HMs in soils by biochar, nonspecific adsorption, and the negative influences of biochar on soil microorganisms and plants. In addition, further research directions and several recommendations (standardization, long-term field experiments, mechanisms research and designer biochars) were also proposed to enable the large-scale application of biochar for the remediation of HM-contaminated soils.

Improvement of humification and mechanism of nitrogen transformation during pig manure composting with Black Tourmaline

This study aimed to reveal the role of Black Tourmaline (TM) in the humification enhancement and the mechanism of nitrogen transformation during pig manure composting. Results showed that adding TM promoted the maturity and improved the humification degree by 20.13-33.77%. And TM was beneficial for the transformation from NH₄⁺-N to amino organic nitrogen to fix more nitrogen in compost mass. Then NH₃ and N₂O volatilization were decreased by 22.88-34.76% and 69.79-87.47% by comparison with the control, and the minimum value in nitrogen loss (26.78%) was observed in the 10% TM blended treatment. Furthermore, through RDA analysis, the protease an upmost contributor to nitrogen transformation. Meanwhile, total organic carbon was dominant factor affected enzymatic activities. Therefore, 10% TM was suggested to reduce nitrogen loss and increase humification in this research. Deeply related research in gene and specific addition amounts of TM will be investigated later.

An analysis of the versatility and effectiveness of composts for sequestering heavy metal ions, dyes and xenobiotics from soils and aqueous milieus

The persistence and bioaccumulation of environmental pollutants in water bodies, soils and living tissues remain alarmingly related to environmental protection and ecosystem restoration. Adsorption-based techniques appear highly competent in sequestering several environmental pollutants. In this review, the recent research findings reported on the assessments of composts and compost-amended soils as adsorbents of heavy metal ions, dye molecules and xenobiotics have been appraised. This review demonstrates clearly the high adsorption capacities of composts for umpteen environmental pollutants at the lab-scale. The main inferences from this review are that utilization of composts for the removal of heavy metal ions, dye molecules and xenobiotics from aqueous environments and soils is particularly worthwhile and efficient at the laboratory scale, and the adsorption behaviors and effectiveness of compost-type adsorbents for agrochemicals (e.g. herbicides and insecticides) vary considerably because of variabilities in structure, topology, bond connectivity, distribution of functional groups and interactions of xenobiotics with the active humic substances in composts. Compost-based field-scale remediation of environmental pollutants is still sparse and arguably much challenging to implement if, furthermore, real-world soil and water contamination issues are to be addressed effectively. Hence, significant research and process development efforts should be promptly geared and intensified in this direction by extrapolating the lab-scale findings in a cost-effective manner.