Influence of clay as additive on greenhouse gases emission and maturity evaluation during chicken manure 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.

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.

Contribution of zeolite to nitrogen retention in chicken manure and straw compost: Reduction of NH3 and N2O emissions and increase of nitrate

Co-composting of chicken manure, straw and zeolite was investigated in a water bath heating system to estimate the effect of zeolite on physicochemical properties and metabolic functions related to nitrogen conversion. The results indicated that NH3 catches by zeolite was concentrated in the early stage and zeolite with 10 % addition reduced 28 % NH3 and 55 % N2O emissions as compost ended. The nitrate content in 10 % zeolite group was 17 % higher than that in control group. There was no significant increase of NO2- in zeolite group. More NO2- formed NH3, rather than being converted to NOx through denitrification. The abundance of nitrification genes amoA and hao increased except nxrA in zeolite groups. Denitrification was the most obvious at 20 d and zeolite decreased the abundance of denitrification genes narG, nirK and nosZ at this time.

Effect of different multichannel ventilation methods on aerobic composting and vegetable waste gas emissions

Aerobic composting, especially semipermeable membrane-covered aerobic fermentation, is known to be an effective method for recycling and reducing vegetable waste. However, this approach has rarely been applied to the aerobic composting of vegetable waste; in addition, the product characteristics and GHG emissions of the composting process have not been studied in-depth. This study investigated the effect of using different structural ventilation systems on composting efficiency and greenhouse gas emissions in a semipermeable membrane-covered vegetable waste compost. The results for the groups (MV1, MV2, and MV3) with bottom ventilation plus multichannel ventilation and the group (BV) with single bottom ventilation were compared here. The MV2 group effectively increased the average temperature by 19.06% whilst also increasing the degradation rate of organic matter by 30.81%. Additionally, the germination index value reached more than 80%, 3 days in advance. Compared to those of the BV group, the CH4, N2O, and NH3 emissions of MV2 were reduced by 32.67%, 21.52%, and 22.57%, respectively, with the total greenhouse gas emissions decreasing by 24.17%. Overall, this study demonstrated a multichannel ventilation system as a new method for improving the composting efficiency of vegetable waste whilst reducing gas emissions.

Molecular insight into the transformation of dissolved organic matter during sewage sludge composting: An investigation of a full-scale composting plant

The aim of the study was to explore the molecular dynamics and transformation pathways of dissolved organic matter (DOM) in sewage sludge (SS) during composting, and the DOM of raw material, material experiencing thermophilic phase and material collected from humification phase were characterized using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry. The results indicated that there were approximately 85% of aliphatic/proteins and 75% of carbohydrate preferentially decomposed in the thermophilic phase. Moreover, lignins/carboxylic-rich alicyclic molecules (CRAM) were the main N-containing substances evolved in the decomposition, which leading to a reduction of N/C ratio from 0.073 to 0.041. Whereas aliphatic acids and tryptophan in lignins/CRAM with high oxidizing capacities are preferentially decomposed in the thermophilic phase. As for maturity phase, the carbon of the newly generated compounds (belonging to lignins/CRAM and tannins), possessed an oxidation state that similar to sulfonates and sulfonamides, and these DOM are beneficial for the humic substances formation. Moreover, it was found that the newly formed N2Ox and N3Ox compounds had a more significant contribution to the double bond equivalent (DBE) of the compost, corresponding to 1.0 and 1.7 DBE, respectively. The results would help explore the understanding of DOM transformation and humification during SS composting in the microscopic molecular level.

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.

DATAMAN: A global database of methane, nitrous oxide, and ammonia emission factors for livestock housing and outdoor storage of manure

Livestock manure management systems can be significant sources of nitrous oxide (N₂ O), methane (CH₄ ), and ammonia (NH₃ ) emissions. Many studies have been conducted to improve our understanding of the emission processes and to identify influential variables in order to develop mitigation techniques adapted to each manure management step (animal housing, outdoor storage, and manure spreading to land). The international project DATAMAN (http://www.dataman.co.nz) aims to develop a global database on greenhouse gases (N₂ O, CH₄ ) and NH₃ emissions from the manure management chain to refine emission factors (EFs) for national greenhouse gas and NH₃ inventories. This paper describes the housing and outdoor storage components of this database. Relevant information for different animal categories, manure types, livestock buildings, outdoor storage, and climatic conditions was collated from published peer reviewed research, conference papers, and existing databases published between 1995 and 2021. In the housing database, 2024 EFs were collated (63% for NH₃ , 19.5% for CH₄ , and 17.5% for N₂ O). The storage database contains 654 NH₃ EFs from 16 countries, 243 CH₄ EFs from 13 countries, and 421 N₂ O EFs from 17 countries. Across all gases, dairy cattle and swine production in temperate climate zones are the most represented animal and climate categories. As for the housing database, the number of EFs for the tropical climate zone is under-represented. The DATAMAN database can be used for the refinement of national inventories and better assessment of the cost-effectiveness of a range of mitigation strategies.

Regulating the exposed crystal facets of α-Fe2O3 to promote Fe2O3-modified biochar performance in heavy metals adsorption

α-Fe₂O₃ modified biochar (Fe₂O₃/BC) was prepared to remove Cu(II), Pb(II) and As(V). By adjusting the calcination temperature, the morphology and exposed crystal facets of α-Fe₂O₃ on the biochar were changed which further affected the adsorption performance. The kinetics and isotherms were investigated systematically to reveal adsorption effect of the adsorbent on Cu(II), Pb(II) and As(V). The results indicated that chemisorption process was the dominant adsorption mechanism. Fe₂O₃/BC-350 exhibited superior adsorption capacity for Cu(II) (258.22 mg/g) and Pb(II) (390.60 mg/g), and Fe₂O₃/BC-250 showed relatively good adsorption capacity for As(V) (5.78 mg/g). By adsorption mechanism analysis, electrostatic adsorption, ion exchange, precipitation and complexation were coexisted in the process of removing metal ions by Fe₂O₃/BC. The repeatability test and the effect of ion strength exhibited the strong stability of Fe₂O₃/BC. Meanwhile, density functional theory (DFT) calculations manifested that the (202) facet of α-Fe₂O₃ on Fe₂O₃/BC-350 possessed the lowest adsorption energies of Cu(II) and Pb(II). While for As(V), it was the (104) facet of α-Fe₂O₃ on Fe₂O₃/BC-250 that exhibited the lowest adsorption energy. DFT results revealed that different Fe₂O₃/BC had different adsorption affinities to various heavy metals. In general, this work not only prepared a promising adsorbent via a simple procedure, but also served as a reference for researchers in designing absorbents with specific active facet for efficient heavy metals remediation.

Effect of hydrothermal pretreatment and compound microbial agents on compost maturity and gaseous emissions during aerobic composting of kitchen waste

Though aerobic composting is commonly used in kitchen waste (KW) disposal, the high-oil and high-salt characteristics of KW could affect composting efficiency and lead to the land using risk of produced fertilizer. The impact of hydrothermal pretreatment (HTP) and addition of compound microbial agent (CMA) on compost maturity, greenhouse gas (GHGs) emissions and bacterial community during the kitchen waste composting were evaluated in the present work. Results indicated that N2O, CH4 and CO2 emissions from treatment by HTP and CMA addition were reduced by 82.72%, 13.77% and 20.78 %, respectively, comparing with the control (without HTP and without CMA addition). The seed germination index (GI) value of the HTP and CMA addition treatment was 1.03 and had the highest maturity in all treatments. Furthermore, the bacterial community analysis indicated that CMA inoculation could increase the relative abundance of genus Bacillus at the thermophilic stage of composting to accelerate organic biodegradation. This work provided important insight into mitigating GHGs emissions and improving compost quality in kitchen waste composting.

Carbon and N conservation during composting: A review

Composting, as a conventional solid waste treatment method, plays an essential role in carbon and nitrogen conservation, thereby reducing the loss of nutrients and energy. However, some carbon- and nitrogen-containing gases are inevitably released during the process of composting due to the different operating conditions, resulting in carbon and nitrogen losses. To overcome this obstacle, many researchers have been trying to optimize the adjustment parameters and add some amendments (i.e., pHysical amendments, chemical amendments and microbial amendments) to reduce the losses and enhance carbon and nitrogen conservation. However, investigation regarding mechanisms for the conservation of carbon and nitrogen are limited. Therefore, this review summarizes the studies on physical amendments, chemical amendments and microbial amendments and proposes underlying mechanisms for the enhancement of carbon and nitrogen conservation: adsorption or conversion, and also evaluates their contribution to the mitigation of the greenhouse effect, providing a theoretical basis for subsequent composting-related researchers to better improve carbon and nitrogen conservation measures. This paper also suggests that: assessing the contribution of composting as a process to global greenhouse gas mitigation requires a complete life cycle evaluation of composting. The current lack of compost clinker impact on carbon and nitrogen sequestration capacity of the application site needs to be explored by more research workers.

Recent trends and advances in composting and vermicomposting technologies: A review

Composting technologies have come a long way, developing from static heaps and windrow composting to smart, artificial intelligence-assisted reactor composting. While in previous years, much attention has been paid to identifying ideal organic waste streams and suitable co-composting candidates, more recent efforts tried to determine novel process-enhancing supplements. These include various single and mixed microbial cultures, additives, bulking agents, or combinations thereof. However, there is still ample need to fine-tune the composting process in order to reduce its impact on the environment and streamline it with circular economy goals. In this review, we highlight recent advances in integrating mathematical modelling, novel supplements, and reactor designs with (vermi-) composting practices and provide an outlook for future developments. These results should serve as reference point to target adjusting screws for process improvement and provide a guideline for waste management officials and stakeholders.

Effect of inoculation with newly isolated thermotolerant ammonia-oxidizing bacteria on nitrogen conversion and microbial community during cattle manure composting

Nitrogen loss during composting is closely related to NH₄⁺-N conversion, and ammonia-oxidizing bacteria (AOB) are important microorganisms that promote NH₄⁺-N conversion. Since the biological activity of conventional AOB agents used for compost inoculation declines rapidly during the thermophilic phase of composting, new compound inoculants should be developed that are active during that phase. In the current study, the effects of inoculating cattle manure compost with newly isolated AOB (5%, v/w) [thermotolerant AOB X-2 strain (T-AOB-2), mesophilic AOB X-4 strain (M-AOB-4), and AOB X-2 combined with AOB X-4 (MT-AOB-2-4)] on the conversion of nitrogen, compost maturity, and the resident microbial community were studied. During 35 days of composting, compared with the control, AOB inoculation reduced NH₃ emissions by 29.98-46.94%, accelerated the conversion of NH₄⁺-N to NO₂^--N, increased seed germination values by 13.00-25.90%, and increased the abundance of the microbial community at the thermophilic phase (16.38-68.81%). Network analysis revealed that Bacillaceae play a crucial role in the composting process, with the correlation coefficients: 0.83 (p < 0.05) with NH₃, 0.64 (p < 0.05) with NH₄⁺-N, and 0.81 (p < 0.05) with NO₂^--N. In addition, inoculation with MT-AOB-2-4 notably increased the total nitrogen content of compost, prolonged the sanitation stage, and promoted compost maturity. Hence, MT-AOB-2-4 may be used to increase the microbial community abundance and improve the efficiency of cattle manure composting.

Impact of composting factors on the biodegradation of lignin in Eichhornia crassipes (water hyacinth): A response surface methodological (RSM) investigation

Water hyacinth (Eichhornia crassipes) is a hydrophyte weed that causes havoc in the aquatic ecosystem as an invasive plant that can obstruct waterways and bring about nutrient imbalance. This study aims to address how this invasive hydrophyte can be physically harvested and biochemically transformed into a bioproduct that can enhance the restoration of damaged soil. Biocomposting, a low-cost biotechnological technique, was designed to degrade the lignocellulosic Eichhornia crassipes biomass and transform it into a valuable bioproduct. The process used response surface methodology (RSM) to investigate the aggregate effect of moisture content, turning frequency, and microbial isolate (Chitinophaga terrae) inoculum size on the breakdown of lignin over 21 days. The moisture content (A), (45, 55, 65) % v/w, inoculum size (B), (5, 7.5, 10)% v/v, and turning frequency (C), (1, 3, 5) days were considered independent variables, while percentage lignin degradation was considered a response variable. The optimal conditions for lignin breakdown were 65.7 percent (v/w) moisture, 7.5 percent (v/v) inoculum concentration, and 5-day interval turning. The R² score of 0.9733 demonstrates the model's integrity and reliability. Thus, the RSM approach resulted in a fine grain dark brown Nutri-compost that proved effective in enhancing soil fertility. This procedure is recommended for a scale-up process where large quantities of the hydrophyte could be treated for conversion into Nutri compost.

Black soldier fly larvae for organic manure recycling and its potential for a circular bioeconomy: A review

Livestock farming and its products provide a diverse range of benefits for our day-to-day life. However, the ever-increasing demand for farmed animals has raised concerns about waste management and its impact on the environment. Worldwide, cattle produce enormous amounts of manure, which is detrimental to soil properties if poorly managed. Waste management with insect larvae is considered one of the most efficient techniques for resource recovery from manure. In recent years, the use of black soldier fly larvae (BSFL) for resource recovery has emerged as an effective method. Using BSFL has several advantages over traditional methods, as the larvae produce a safe compost and extract trace elements like Cu and Zn. This paper is a comprehensive review of the potential of BSFL for recycling organic wastes from livestock farming, manure bioconversion, parameters affecting the BSFL application on organic farming, and process performance of biomolecule degradation. The last part discusses the economic feasibility, lifecycle assessment, and circular bioeconomy of the BSFL in manure recycling. Moreover, it discusses the future perspectives associated with the application of BSFL. Specifically, this review discusses BSFL cultivation and its impact on the larvae's physiology, gut biochemical physiology, gut microbes and metabolic pathways, nutrient conservation and global warming potential, microbial decomposition of organic nutrients, total and pathogenic microbial dynamics, and recycling of rearing residues as fertilizer.

The important role of tricarboxylic acid cycle metabolism pathways and core bacterial communities in carbon sequestration during chicken manure composting

As a kind of livestock manure, chicken manure (CM) was rich in organic matter and microorganisms. However, a large amount of foul gas discharged by its random stacking not only threatened the environment, but also caused harm to human health. In view of the serious carbon loss and the unclear action mechanism of microbial community on carbon metabolism during CM composting, the effect of adding regulators on the sequestration of organic carbon was explored. Therefore, the purpose of this study was to explore the regulation mechanism of adding tricarboxylic acid cycle (TCA cycle) regulators on the core carbon metabolism pathway during CM composting. The results showed that the adenosine triphosphate (ATP) and malonic acid (MA) slowed down organic carbon degradation, resulting in lower carbon loss rate, which were 64.99% (CK), 62.35% (MA), and 61.26% (ATP) in each treatment. By comparing the abundance and structure of the carbon-related bacterial communities in different treatments, it was found that adding ATP and MA not only reduced the bacterial community abundance, but also tended to be similar in bacterial community composition. Moreover, the microbial specificity related to carbon metabolism pathway was enhanced, while the related gene expression and gene abundance were weakened. The regulation of TCA cycle metabolism pathway was confirmed to be the main way to improve organic carbon content. These findings revealed the positive effects of ATP and MA on carbon fixation from the perspective of gene metabolism.

Evaluation of Co-Composting as an Alternative for the Use of Agricultural Waste of Spring Onions, Chicken Manure and Bio-Waste Produced in Moorland Ecosystems

Composting is an adequate method for treating and valorizing agricultural waste such as those from spring onion (SO) cultivation and chicken breeding (chicken manure–CM). However, the low content of Total Organic Carbon in the waste from SO and the high concentration of total nitrogen in CM are limitations for the composting process. This research studied the co-composting of SO and CM in a moorland ecosystem, together with locally available co-substrates such as biowaste (BW) and woodchips (WC), focusing on the effect of co-composting in process development and end-product quality. A pilot-scale experiment was carried out using three treatments in triplicated composting piles: (i) Treatment A: 43% CM + 41% BW + 16% WC; (ii) Treatment B: 52% CM + 32% SO + 16% WC, and (iii) Treatment C: 70% SO + 30% WC. Treatments A and B reached thermophilic temperatures after two days of the process start and remained at that level for 17 days. However, treatment B reached environmental temperature during curing in a shorter time (43 days) than treatment A (53 days). Treatment C did not achieve thermophilic temperatures. Tests carried out at the end of the process showed end-product stability and non-phytotoxic characteristics (germination indexes 80%). The fertility index of the products showed that treatments A and B presented values of 4.3 (over 5.0) while treatment C obtained a value of 2.5. From the perspective of agricultural use, products from the three treatments had limitations due to deficiencies in essential nutrients like phosphorus. Still, they had potential as a soil amendment for restoration processes. In summary, we have demonstrated that this waste, in combination with other organic materials, could be a good amendment for the composting process and the end product.

Roles of organic matter transformation in the bioavailability of Cu and Zn during sepiolite-amended pig manure composting

The application of clay minerals facilitates the bioavailability of heavy metals and the humification in livestock manure composting. However, whether the humification plays a critical role in the bioavailability of heavy metals is still unclear. Here, with the addition of sepiolite (SEP), the fractions of Cu and Zn, and the spectral characteristics of humic acids (HAs) during aerobic pig manure composting were investigated. The SEP-amended composting had a decreased peak temperature and an increased electrical conductivity, regardless of the SEP dosage. The seed germination index increased by 15.9 ± 0.5% (p < 0.05) with the appropriate dosage of SEP (6%), indicating a higher maturity and a lower phytotoxicity of the SEP-amended compost. The addition of SEP reduced the water-extractable organic matter (WEOM) content and increased the percentage of HAs by 2.8-10.7%. More interestingly, during SEP-amended composting, the reducible fraction of heavy metals was transformed into the oxidizable fraction, and the bioavailability of Cu and Zn decreased by 11.0-15.9% and 15.4-26.5%, respectively. Ultraviolet-visible (UV-vis) spectra and fluorescence spectra analyses showed that the SUVA₂₅₄ and complex fluorescent components of HAs in the SEP-amended composting increased by 4.4-15.8% and 1.2-9.0%, respectively. Nuclear magnetic resonance (NMR) further confirmed that the addition of SEP increased the aromatic index and percentage of carbonyl-carboxyl C of HAs by 3.4-8.3% and 4.6-5.7%, respectively. The redundancy analyses (RDA) described the SUVA₂₅₄, aromatic index and carbonyl-carboxyl C of HAs had a strong positive correlation with the oxidizable fraction of heavy metals, which was further confirmed by variance partitioning analysis (VPA). Overall, this work suggested that the HAs structure play an important role in the bioavailability of Cu and Zn during SEP-amended composting, potentially providing safe organic fertilizer.

Effect of attapulgite on heavy metals passivation and microbial community during co-composting of river sediment with agricultural wastes

This paper investigated the effects of attapulgite addition on the physicochemical processes, heavy metal transformation, and microbial community during the composting of agricultural wastes and sediment. In addition, the correlation between environmental factors, heavy metals (HMs), and microbial community was also assessed by redundancy analysis (RDA). The results showed that pile B with attapulgite addition entered the thermophilic phase earlier and lasted longer than pile A as the control group. The reduction in the bioavailability of HMs (Cr, Cd, and Zn) was also greater in pile B, and the passivation of HMs was ranked as Cd > Zn > Cr. The relative abundance of phylum Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria was the highest throughout the composting process. Furthermore, the RDA showed that the bacterial community composition was significantly correlated with temperature and C/N ratio in pile A, while significantly correlated with organic matter and pH in pile B. And the addition of attapulgite facilitated the conversion of HMs into more stable fractions by Pseudomonas. The study would provide a reference for the application of attapulgite to remediate the river sediment polluted by HMs.

Effects of thermophiles inoculation on the efficiency and maturity of rice straw composting

The present study investigated the effects of separately or simultaneously inoculating thermophilic fungus Aspergillus fumigatus Z5 and bacterium Geobacillus stearothermophilus B5 on lignocellulose degradation, enzyme activities and humification during rice straw composting. The results indicated that inoculation of Z5 accelerated the rise of temperature in the mesophilic phase, and the degradation degree of cellulose and hemicellulose was increased by 25.3% and 20.7%, respectively, due to the higher activities of lignocellulolytic enzymes. Inoculation of B5 increased 5-7 °C of the compost temperature in the thermophilic phase, and also prolonged the duration from 33 to 41 days. Inoculated simultaneously, the secreted hydrolases of Z5 generated more nutrition and promoted the growth of B5. B5 maintained and increased the compost temperature, thus presenting a better hydrolysis environment for extracellular hydrolases. Thermophilic inoculation altered the main physicochemical factors and improved efficiency and maturity in rice straw composting.

Dynamics of fungal species related to nitrogen transformation and their network patterns during cattle manure-corn straw with biochar composting

Fungi are reputed to play a significant role in the composting matrix as decomposers of recalcitrant organic materials like cellulose and lignin. However, information on the fungi communities' roles in nitrogen transformation under a compost-biochar mixture is scarce. This study investigated shifts in fungal species mediating N transformation and their network patterns in cattle manure-corn straw (CMCS) and CMCS plus biochar (CMCB) composting using high-throughput sequencing data. The results revealed that the addition of biochar altered fungal richness and diversity and significantly influenced their compositions during composting. Biochar also altered the compost fungal network patterns; CMCS had a more complex network with higher positive links than CMCB, suggesting stable niche overlap. The consistent agreement of multivariate analyses (redundancy, network, regression, Mantel and path analyses) indicated that Ciliophora_sp in CMCS and unclassified_norank_Pleosporales in CMCB were the key fungal species mediating total N transformation, whereas Scedosporium_prolificans in CMCS and unclassified_Microascaceae in CMCB were identified as major predictive indices determining NO₃^--N transformation. Also, Coprinopsis cinerea and Penicillium oxalicum were the predictive factors for NH₄⁺-N transformation in CMCS and CMCB during composting. These results indicated that the effects of biochar on N conversions in composting could be unraveled using multivariate analyses on fungi community evolution, network patterns, and metabolism.

Toxicity and physicochemical parameters of composts including distinct residues from agribusiness and slaughterhouse sludge

Composting is useful for treatment of residues from agribusiness, but the potential toxicity of the final compost should be evaluated before its agricultural destination. The objective of this study was to evaluate the physicochemical characteristics and the toxicity of agribusiness residues using onion seeds as bioindicators. All tested treatments were composed by sludge from a swine slaughterhouse and sawdust. Besides the control, which included no additional materials, the other treatments included aviary bedding, rice husk and residue from tobacco industries as structuring materials. After 120 days of composting, for all treatments, the temperature inside the composting piles approached the environmental temperature, the physicochemical parameters indicated that the composts were stabilized and, except for the treatment including tobacco residues, that could be used for agriculture without impairing plant germination. Although the treatments including tobacco residues and rice husk showed evidence of cytotoxicity and genotoxicity at the beginning of the composting period, that was not observed for the treatment including aviary bedding. Such potential toxicity was not observed at the end of composting for any of the tested treatments.

Effects of bulking agents on greenhouse gases and related genes in sludge composting

The effect of organic bulking agents on CO₂, NH₃, N₂O and CH₄ emission and related genes was evaluated in 40 days sludge composting with wood chip, wheat straw and rice husk, respectively. The results showed wood chip had the highest C/N of 111.3, total porosity of 93.13% and aeration porosity of 78.98% among three bulking agents. Wheat straw had the highest water-holding porosity of 25.62%, which could be critical factor increasing CH₄ production and reducing NH₃ emission. Moreover, there was no significant difference in N₂O emission rates in three composting systems with three bulking agents. RDA analysis showed a negative correlation between mcrA and NH + 4-N. Nitrate content in raw feedstock was dominant factor limiting N₂O yield due to low amoA. The continuous increase of oxidation-reduction potential was significantly positive correlated with pmoA and negative correlation with nirK and norB, which reduced N₂O and CH₄ production in the curing period.

Selection of sensitive seeds for evaluation of compost maturity with the seed germination index

The seed germination index (GI) is a widely used indicator of compost maturity and is a required index in many national standards. However, seeds of different species vary markedly in sensitivity to the biological toxicity of compost. Therefore, suitable seed selection is essential for evaluation of compost maturity with the GI. This study systematically investigated the germination percentage and root length for seeds of 17 species incubated in deionized water for 48 h at 25 °C in the dark. Based on the germination percentage, seeds of eight species (white radish, cucumber, fruit radish, edible rape, round radish, hybrid cucumber, cress, and Chinese cabbage) were selected for determination of the GI of chicken manure composted with differing proportions of tobacco powder and mushroom substrate. The GI of hybrid cucumber seeds showed a significant positive correlation with temperature and pH, and a significant negative correlation with E₄/E₆ ratio and ammonium-nitrogen content. The change in GI of hybrid cucumber seeds during composting and the GI value at the completion of composting were consistent with other maturity indicators. Among the tested seeds, the biological toxicity of the compost was best characterized by hybrid cucumber seeds, which thus represented a sensitive and reliable seed suitable for evaluation of compost maturity with the GI.

Bioengineered biochar as smart candidate for resource recovery toward circular bio-economy: a review

Biochar's ability to mediate and facilitate microbial contamination degradation, as well as its carbon-sequestration potential, has sparked interest in recent years. The scope, possible advantages (economic and environmental), and future views are all evaluated in this review. We go over the many designed processes that are taking place and show why it is critical to look into biochar production for resource recovery and the role of bioengineered biochar in waste recycling. We concentrate on current breakthroughs in the fields of engineered biochar application techniques to systematically and sustainable technology. As a result, this paper describes the use of biomass for biochar production using various methods, as well as its use as an effective inclusion material to increase performance. The impact of biochar amendments on microbial colonisation, direct interspecies electron transfer, organic load minimization, and buffering maintenance is explored in detail. The majority of organic and inorganic (heavy metals) contaminants in the environment today are caused by human activities, such as mining and the use of chemical fertilizers and pesticides, which can be treated sustainably by using engineered biochar to promote the establishment of a sustainable engineered process by inducing the circular bioeconomy.

Composting-a solution of eliminating a nitrite-rich wastewater by reusing it as a moisture conditioning agent

Composting could be applied to dispose various organic solid wastes and liquid wastes. Literature suggested that reusing a nitrogen-rich wastewater as a composting moisture conditioning agent could promote the maturity and nitrogen content of compost. However, it's unclear whether a nitrite-rich wastewater could be eliminated by composting because of the toxicity of nitrite. In this study, a nitrite-rich wastewater (STL, pH = 7.9) was reused as a composting moisture conditioning agent. The influence of STL reusing period (i.e., adding STL from the first day of mesophilic, thermophilic, and cooling period, and the addition lasted for 10 days) on composting performance was also discussed. Results revealed that organic matter decomposition was strongly suppressed by high concentration of free nitrous acid when STL was added in mesophilic period, whereas the organic matter hydrolysis was prompted when STL was added in thermophilic and cooling period. STL addition enhanced nitrification at high temperatures during composting, thus increasing the nitrate content of compost by 2-10 times compared with that of the control group (using tap water as a moisture conditioning agent). Nitrite addition also stimulated nitrous oxide emissions yielded by biotic or chemical processes during STL addition, especially under the transient condition at 50°C-55 °C, and resulted in a 28%-39% increase in greenhouse gas emissions compared with that of the control group. Therefore, the composting could be a solution of eliminating a nitrite-rich wastewater by reusing it as a moisture conditioning agent when nitrous oxide emission issue was properly addressed.

Evaluation of Maturity and Greenhouse Gas Emission in Co-Composting of Chicken Manure with Tobacco Powder and Vinasse/Mushroom Bran

This study investigated the effects of different proportions (0%, 5%, 10%, 15%) of bulking agent (vinasse, mushroom bran, and tobacco powder) on maturity and gaseous emissions in chicken manure composting. The results showed that all of the treatments reached the standard of harmless disposal. With the exception of the control treatment, the CH4, N2O, and NH3 emissions in the treatments that had been prepared using the addition of mixed bulking agents were effectively reduced by 2.9–30.6%, 8.30–80.9%, and 37.3–26.6%; their compost maturity also met the Chinese national standard. Specifically, 10% mushroom bran combined with 5% tobacco powder was the optimal combination for simultaneously improving the maturity and reducing greenhouse gas emission in chicken manure composting.

Effects of the functional membrane covering on the gas emissions and bacterial community during aerobic composting

The effects of the functional membrane covering on the gas emissions and bacterial community during dairy cow manure aerobic composting were investigated. A lab-scale aerobic composting experiment was conducted with the control group (CK), Gore group (Gore), and ZT group (ZT), namely, without and with two functional membranes. Covering the functional membrane retained heat and improved the seed germination index in Gore and ZT groups. Compared with the CK group, the Gore membrane decreased NH₃ and N₂O emissions by 11.77% and 26.40%, respectively. The ZT membrane decreased N₂O and CO₂ emissions by 68.44% and 1.56%, respectively. The Gore and ZT membranes decreased the global warming potential by 16.97% and 53.41%, respectively. Moreover, Covering the two functional membranes improved the Actinobacteria relative abundance and were conducive to the degradation of volatile solid. Altogether, membrane-covered aerobic composting is an important technology for the resource utilization of organic waste.

Evaluation of cornstalk as bulking agent on greenhouse gases emission and bacterial community during further composting

The aim of current work was to explore the impact of Cornstalk (CS) on greenhouse gaseous emission and maturation during further composting and analyzed its impact on bacterial diversity. Three kinds of immature fertilizers were collected from chicken, pig and dairy manure namely T1, T2 and T3 as control, T4, T5 and T6 were added CS into T1 to T3 and adjusted C/N to 25 namely treatment. The results illustrated that gases (N₂O, CH₄ and NH₃) emission of CS added treatments decreased by 6.39%-24.68%, 10.60%-23.23% and 13.00%-19.58%, respectively. But the CS amendment increased CO₂ emission by 15.53%-30.81%. The mineralization of carbon and nitrogen was mainly correlated to Firmicutes, Actinobacteria, Proteobacteria and Bacteroidota, CS amendment increased abundance by 22.28%, 17.79%, 1.48% and 35.90%, respectively. The strategy of employing CS would be the most feasible approach for recycling of immature manure, considering its compost quality and environmental from farm.

Sustainability of the Dairy Industry: Emissions and Mitigation Opportunities

Dairy cattle provide a major benefit to the world through upcycling human inedible feedstuffs into milk and associated dairy products. However, as beneficial as this process has become, it is not without potential negatives. Dairy cattle are a source of greenhouse gases through enteric and waste fermentation as well as excreting nitrogen emissions through their feces and urine. However, these negative impacts vary widely due to how and what these animals are fed. In addition, there are many promising opportunities for further reducing emissions through feed and waste additives. The present review aims to further expand on where the industry is today and the potential avenues for improvement. This area of research is still not complete and additional information is required to further improve our dairy systems impact on sustainable animal products.

Bacterial agents affected bacterial community structure to mitigate greenhouse gas emissions during sewage sludge composting

The present work studied the influence of bacterial agents (B1, B2) and bamboo biochar (BB) on greenhouse gas emissions and bacterial community during the sewage sludge composting. Results showed that compared with CK, the total methane emissions ofC, B1, B1C, B2, and B2C treatments declined by 16.4%, 25.2%, 45.4%, 7.8%, and 44.4%, respectively. The total N₂O emissions ofC and B1C treatments declined by 5.1% and 3.7% while B1, B2, and B2C treatments increased the total N₂O emissions by 6.7%, 21.6%, and 10.4%, respectively. These results illustrated that the addition of BB is conducive for reducing greenhouse gas emissions while different bacterial agents have various effects. According to pearson correlation analysis, N₂O emissions and Acidimicrobiia, Alphaproteobacteria, Gammaproteobacteria, and Tepidiformia have strong negative correlation while positive correlation with Bacilli and Clostridia. Methane emissions have a strong negative correlation with Actinobacteria. CO₂ emissions have a strong positive correlation with Bacilli.

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.

Influence of reusable polypropylene packing on ammonia and greenhouse gas emissions during sewage sludge composting-a lab-scale investigation

Bulking agents are particularly important for sewage sludge composting. In this study, reusable polypropylene packing (RPP) was mixed with sawdust to improve composting. The effect of the mix ratio of sawdust and RPP on the physicochemical characteristics, nitrogen transformation, and emissions of greenhouse gas (GHG) as well as differences in the germination index values was detected in a lab-scale composting experiment. The results showed that the unique use of RPP as a bulking agent increased the moisture content over 70%, which resulted in poorer porosity and a less efficient O₂ utilization environment and thus suppressed the degradation of organic matter. The highest CH₄ 9275.8 mg and lowest CO₂ 202.6 g emissions were detected after 25 days of composting in the treatment with RPP used as a bulking agent. When the mixing ratio of sawdust and RPP was 1:1, the temperature, oxygen supply, and dissolved organic carbon degradation were improved. The NH₃, N₂O, and CH₄ emissions were reduced by 32.2, 18.3, and 90.7% compared with a treatment with RPP as a unique bulking agent. The RPP had no effect on conserving nitrogen during sludge composting; the total nitrogen loss was reduced from 29.3 to 18.2% when sawdust was mixed with RPP in a ratio of 1:1. Therefore, mixing RPP and sawdust in the dry weight ratio of 1:1 (sawdust: RPP) can be potentially used for reducing composting cost and improving the sewage sludge composting by reducing the amount of sawdust mixed and mitigating GHG and NH₃ emissions.

Gases emission during the continuous thermophilic composting of dairy manure amended with activated oil shale semicoke

NH₃ and greenhouse gases emission are big problems during composting, which can cause great nitrogen nutrient loss and environmental pollution. This study investigated effects of the porous bulking agent of oil shale semicoke and its activated material on the gases emission during the continuous thermophilic composting. Results showed addition of semicoke could significantly reduce the NH₃ emission by 74.65% due to its great adsorption capacity to NH₄⁺-N and NH₃, further the effect could be enhanced to 85.92% when utilizing the activated semicoke with larger pore volume and specific surface area. In addition, the CH₄ emission in the semicoke and activated semicoke group was also greatly mitigated, with a reduction of 67.23% and 87.62% respectively, while the N₂O emission was significantly increased by 93.14% and 100.82%. Quantification analysis of the functional genes found the abundance of mcrA was high at the massive CH₄-producing stage and the archaeal amoA was dominant at the N₂O-producing stage in all the composting groups. Correlation and redundancy analysis suggested there was a positive correlation between the CH₄ emission and mcrA. Addition of semicoke especially activated semicoke could reduce the CH₄ production by inhibiting the methanogens. For the NH₃ and N₂O, it was closely related with the nitrification process conducted by archaeal amoA. Addition of semicoke especially activated semicoke was beneficial for the growth of ammonia-oxidizing archaea, causing the less NH₄⁺-N transformation to NH₃ but more N₂O emission.

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.

Re-using ammonium-rich wastewater as a moisture conditioning agent during composting thermophilic period improves composting performance

A weakly acidic ammonium-rich wastewater (STL) was intended to reuse as a moisture conditioning agent for composting to increase nitrogen content of compost. The influence of adding STL in the mesophilic period (MP), thermophilic period (TP), and cooling period (CP) on composting performance was investigated. Results revealed that organic degradation was strongly suppressed in MP, whereas no difference (p > 0.05) was observed between CP and control group (using tap water as moisture conditioning agent). The hydrolysis and mineralization of organic matter in TP were partly stimulated because reusing STL reduced free ammonia concentrations (<400 mg/L) of windrows. Additionally, the ammonium and nitrate nitrogen content of compost in TP increased by 71% and 425% without additional greenhouse gas emissions compared with control group. Therefore, ammonium-rich wastewater like STL could substitute tap water to condition compost moisture content and increase the nitrogen content of compost during the thermophilic composting period.

The action difference of metabolic regulators on carbon conversion during different agricultural organic wastes composting

The purpose of this study is to explore the action characteristics of metabolic regulators like adenosine tri-phosphate (ATP) and malonic acid (MA) during rice straw (RS) and fruit and vegetable waste (FVW) composting. Results showed that due to the easy degradation difference, ATP and MA reduced CO₂ emission in RS and FVW, respectively. Moreover, adding ATP and MA increased humic acids (HA) content in FVW more significantly (p < 0.05), especially for ATP. However, adding MA accelerated organic matter degradation during RS composting, which was basically consistent with CO₂ emission, but it was not effective in promoting HA formation. Furthermore, the microbial community was reshaped by adding ATP and MA. Eventually, structural equation model further confirmed that adding metabolic regulators enhanced the biotic and abiotic pathways of HA formation, and the promotion effect of adding ATP was more obvious. The study has great practical significance for the dispose of agricultural waste.

Corn cobs efficiently reduced ammonia volatilization and improved nutrient value of stored dairy effluents

Dairy farms produce considerable quantities of nutrient-rich effluent, which is generally stored before use as a soil amendment. Unfortunately, a portion of the dairy effluent N can be lost through volatilization during open pond storage to the atmosphere. Adding of covering materials to effluent during storage could increase contact with NH₄⁺ and modify effluent pH, thereby reducing NH₃ volatilization and retaining the effluent N as fertilizer for crop application. Here the mitigation effect of cover materials on ammonia (NH₃) volatilization from open stored effluents was measured. A pilot-scale study was conducted using effluent collected at the Youran Dairy Farm Company Limited, Luhe County, Jiangsu, China, from 15 June to 15 August 2019. The study included seven treatments: control without amendment (Control), 30-mm × 25-mm corn cob pieces (CC), light expanded clay aggregate - LECA (CP), lactic acid (LA) and lactic acid plus CC (CCL), CP (CPL) or 20-mm plastic balls (PBL). The NH₃ emission from the Control treatment was 120.1 g N m^-2, which was increased by 38.1% in the CP treatment, possibly due to increased effluent pH. The application of CC reduced NH₃ loss by 69.2%, compared with the Control, possibly due to high physical resistance, adsorption of NH₄⁺ and effluent pH reduction. The lactic acid amendment alone and in combination with other materials also reduced NH₃ volatilization by 27.4% and 31.0-46.7%, respectively. After 62 days of storage, effluent N conserved in the CC and CCL treatments were 21.0% and 22.0% higher than that in the Control (P < 0.05). Our results suggest that application of corn cob pieces, alone or in combination with lactic acid, as effluent cover could effectively mitigate NH₃ volatilization and retain N, thereby enhancing the fertilizer value of the stored dairy effluent and co-applied as a soil amendment after two months open storage.

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.

Use of an in situ thermoelectric generator for electric field-assisted aerobic composting

Electric field-assisted aerobic composting (EAAC) is a simple and effective process. To further improve the EAAC process and make good use of waste heat during composting, in this study, we designed an in situ thermoelectric generator using thermoelectric sheets and applied it for EAAC. The findings show that the voltage generated was 8.8-18.6 V, and the maximum power was over 7 W. A direct current-to-direct current (DC-DC) voltage converter was used to stabilize the output at 6.0 V. Self-powered EAAC (sp-EAAC) enhanced compost maturity compared to conventional aerobic composting (CAC). The germination index reached 118% and 88% in sp-EAAC and CAC, respectively, at the end of composting. This work verified that the temperature gap between compost and the environment could be used for the EAAC process, opening a new way to recover waste heat during aerobic composting and accelerate compost maturity.

Influence of fine coal gasification slag on greenhouse gases emission and volatile fatty acids during pig manure composting

This study was evaluated industrial waste fine coal gasification slag (FCGS) as an additive on pig manure composting by parameters of greenhouse gases, NH₃, volatile fatty acids (VFAs) and maturity. Six treatments of FCGS (0%, 2%, 4%, 6%, 8% and 10%) were added into the mixture raw material and composted 42 days. Results illustrated that the FCGS amendment could prolong sanitation stage and promote the degree of maturity, germination index and C/N ratio during composting. With the increasing amendment of FCGS, GI was increased from 9.97 to 28.45%. Compared with control, increasing of FCGS proportion could reduce the mitigation of global warming potential (N₂O and CH₄), NH₃ and cumulative of VFAs from 8.89-77.04%, 3.81-71.65%, 5.18-28.02% and 8.79-83.33%. Finally, present study results revealed that 10%FCGS could improve composting and reduced the maturity period as well as compost quality, thus recommended as effective dosage for efficient pig manure composting.

Effects of inoculation with lignocellulose-degrading microorganisms on nitrogen conversion and denitrifying bacterial community during aerobic composting

The present study compared the effects of inoculation (WSD treatment) and non-inoculation (CK treatment) with lignocellulose-degrading microorganisms on nitrogen conversion, nitrogen functional genes, and the denitrifying bacterial community during aerobic composting, and their potential relations to NH₃ and N₂O emissions were also explored. Results showed that, WSD reduced the NH₃ and N₂O emissions by 25.9% and 34.98%, respectively, compared with CK. WSD also reduced the abundances of nitrifying (bacteria amoA) and denitrifying (nirS, nirK, and nosZ) genes during composting, which were significantly positively correlated with N₂O emissions (P < 0.01). The most important nosZ denitrifying microorganisms belonged to Proteobacteria. Redundancy analysis showed that environmental factors could affect the succession of the denitrifying bacterial community during composting. Based on these results, structural equation modeling demonstrated that the reduction in N₂O emissions under WSD was related to the lower accumulation of NO₃^--N utilized by denitrifying microorganisms during the compost maturation period.

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.

Effect of red kaolin on the diversity of functional genes based on Kyoto Encyclopedia of Genes and Genomes pathways during chicken manure composting

The transcription and expression of functional genes governed the biotransformation of nutrients during composting. In this study, the diversities of functional genes were investigated in 50 days chicken manure composting through six treatments amended with different dosage of red kaolin. Results showed that based on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation, Metabolism possessed largest proportion and richest genes number among six pathways, of which carbohydrate metabolism (81007) were significantly greater than others; while Human Disease and Organismal Systems were relatively lower. Meanwhile, the addition of red kaolin has an important impact on dynamics of KEGG genes, the relative abundance of detected genes were distinctively different in all treatments. Similarity analysis also showed the varying influence of different proportion of red kaolin on functional genes during chicken manure composting. In conclusion, application of red kaolin in chicken manure composting effectively improved the relative abundance of functional genes.

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

The effects of chicken manure biochar (CMB) and chicken manure integrated microbial consortium (CMMC) as co-amendments were assessed on compost maturity and reduction of greenhouse gases and ammonia (NH₃) emissions during chicken manure composting. Composting was conducted using six combinations of CMB and CMCC (0 % CMB + 0 % CMMC, 0 % CMB + 10 % CMMC, 2 % CMB + 10 % CMMC, 4 % CMB + 10 % CMMC, 6 % CMB + 10 % CMMC, 10 % CMB + 10 % CMMC added on a dry weight basis) in six polyvinyl chloride composting reactors for 42 days under an aerobic environment. Co-amendment of CMB and CMMC extended the thermophilic stage and promoted compost maturity. The release of greenhouse gases [nitrous oxide (N₂O) and methane (CH₄)] and NH₃ from treatments co-amended by CMB and CMMC were reduced by 19.0-27.4 %, 9.3-55.9 % and 24.2-56.9 %, respectively, compared with the control. In addition, a redundancy analysis showed that the C/N ratio and temperature had a significant relationship with greenhouse gases and NH₃ emissions among all physiochemical characteristics.