Exploring the mechanisms of decreased methane during pig manure and wheat straw aerobic composting covered with a semi-permeable membrane

Efficient elimination of antibiotic resistome in livestock manure by semi-permeable membrane covered hyperthermophilic composting

Livestock manure is a hotspot for antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), and an important contributor to antibiotic resistance in non-clinical settings. This study investigated the effectiveness and potential mechanisms of a novel composting technology, semi-permeable membrane covered hyperthermophilic composting (smHTC), in removal of ARGs and MGEs in chicken manure. Results showed that smHTC was more efficient in removal of ARGs and MGEs (92% and 93%) compared to conventional thermophilic composting (cTC) (76% and 92%). The efficient removal in smHTC is attributed to direct or indirect negative effects caused by the high temperature, including reducing the involvement of bio-available heavy metals (HMs) in co-selection processes of antibiotic resistance, decreasing the bacterial abundance and diversity, suppressing the horizontal gene transfer and killing potential ARGs hosts. Overall, smHTC can efficiently remove the resistome in livestock manure, reducing the risk to crops and humans from ARGs residues in compost products.

Micro-positive pressure significantly decreases greenhouse gas emissions by regulating archaeal community during industrial-scale dairy manure composting

In this study, the effects of micro-positive pressure formed by covering with a semipermeable membrane in the heating phase of dairy manure composting on greenhouse gas emissions and the mechanism of reducing methane emissions by the archaeal community were investigated. A large-scale experiment was conducted with semipermeable membrane-covered composting (SMC), forced aeration composting (FAC), and traditional static composting (TSC) groups. The results showed that the oxygen concentration and methanogen abundance were key factors in regulating methane emissions. In the heating phase of SMC, the micro-positive pressure could enhance the O2 utilization rate and heating rate, resulting in Methanobrevibacter and Methanobacterium greatly decreasing, and the abundance of mcrA decreased by 90.03%, while that of pmoA did not increase. Compared with FAC and TSC, the cumulative methane emissions in SMC decreased by 51.75% and 96.04%, respectively. Therefore, the micro-positive pressure could effectively reduce greenhouse gas emissions by inhibiting the growth of methanogens.

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

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

Semi-permeable membrane-covered high-temperature aerobic composting: A review

Semi-permeable membrane-covered high-temperature aerobic composting (SMHC) is a suitable technology for the safe treatment and disposal of organic solid waste as well as for improving the quality of the final compost. This paper presents a comprehensive summary of the impact of semi-permeable membranes centered on expanded polytetrafluoroethylene (e-PTFE) on compost physicochemical properties, carbon and nitrogen transformations, greenhouse gas emission reduction, microbial community succession, antibiotic removal, and antibiotic resistance genes migration. It is worth noting that the semi-permeable membrane can form a micro-positive pressure environment under the membrane, promote the uniform distribution of air in the heap, reduce the proportion of anaerobic area in the heap, improve the decomposition rate of organic matter, accelerate the decomposition of compost and improve the quality of compost. In addition, this paper presents several recommendations for future research areas in the SMHC. This investigation aims to guide for implementation of semi-permeable membranes in high-temperature aerobic fermentation processes by systematically compiling the latest research progress on SMHC.

Effect of heterogeneous fenton-like pretreatment on semi-permeable membrane-covered co-composting: Humification and microbial community succession

This study focused on the impacts of heterogeneous Fenton-like pretreatment on the humification and bacterial community during co-composting of wheat straw with cattle dung covered with a semi-permeable membrane. In this study, FeOCl and low concentration of H2O2 were used for pretreatment and composting, which lasted for 39 days. The results showed that the pretreatment promoted the humification process, with degree of polymerization and percentage of humic acid increasing by 53.2 % and 7.3 %, respectively. Furthermore, the diversity and structure of bacterial communities were altered by pretreatment. During the thermophilic phase, pretreatment considerably promoted the metabolism of carbohydrate. According to redundancy analysis, C/N, moisture and organic matter were the key environmental factors that dominated the microbial community. In summary, heterogeneous Fenton-like pretreatment provided a novel idea for improving the humic acid content and maturity of the compost pile.

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.

Uncertainty in non-CO2 greenhouse gas mitigation contributes to ambiguity in global climate policy feasibility

Despite its projected crucial role in stringent, future global climate policy, non-CO₂ greenhouse gas (NCGG) mitigation remains a large uncertain factor in climate research. A revision of the estimated mitigation potential has implications for the feasibility of global climate policy to reach the Paris Agreement climate goals. Here, we provide a systematic bottom-up estimate of the total uncertainty in NCGG mitigation, by developing 'optimistic', 'default' and 'pessimistic' long-term NCGG marginal abatement cost (MAC) curves, based on a comprehensive literature review of mitigation options. The global 1.5-degree climate target is found to be out of reach under pessimistic MAC assumptions, as is the 2-degree target under high emission assumptions. In a 2-degree scenario, MAC uncertainty translates into a large projected range in relative NCGG reduction (40-58%), carbon budget (±120 Gt CO₂) and policy costs (±16%). Partly, the MAC uncertainty signifies a gap that could be bridged by human efforts, but largely it indicates uncertainty in technical limitations.

Pretreatment and composting technology of agricultural organic waste for sustainable agricultural development

With the continuous development of agriculture, Agricultural organic waste (AOW) has become the most abundant renewable energy on earth, and it is a hot spot of research in recent years to realize the recycling of AOW to achieve sustainable development of agricultural production. However, lignocellulose, which is difficult to degrade in AOW, greenhouse gas emissions, and pile pathogenic fungi and insect eggs are the biggest obstacles to its return to land use. In response to the above problems researchers promote organic waste recycling by pretreating AOW, controlling composting conditions and adding other substances to achieve green return of AOW to the field and promote the development of agricultural production. This review summarizes the ways of organic waste treatment, factors affecting composting and problems in composting by researchers in recent years, with a view to providing research ideas for future related studies.

Co-composting of cattle manure and wheat straw covered with a semipermeable membrane: organic matter humification and bacterial community succession

Semipermeable membrane-covered composting is one of the most commonly used composting technologies in northeast China, but its humification process is not yet well understood. This study employed a semipermeable membrane-covered composting system to detect the organic matter humification and bacterial community evolution patterns over the course of agricultural waste composting. Variations in physicochemical properties, humus composition, and bacterial communities were studied. The results suggested that membrane covering improved humic acid (HA) content and degree of polymerization (DP) by 9.28% and 21.57%, respectively. Bacterial analysis indicated that membrane covering reduced bacterial richness and increased bacterial diversity. Membrane covering mainly affected the bacterial community structure during thermophilic period of composting. RDA analysis revealed that membrane covering may affect the bacterial community by altering the physicochemical properties such as moisture content. Correlation analysis showed that membrane covering activated the dominant genera Saccharomonospora and Planktosalinus to participate in the formation of HS and HA in composting, thus promoting HS formation and its structural complexity. Membrane covering significantly reduced microbial metabolism during the cooling phase of composting.

Effects of functional membrane coverings on carbon and nitrogen evolution during aerobic composting: Insight into the succession of bacterial and fungal communities

Carbon and nitrogen evolution and bacteria and fungi succession in two functional membrane-covered aerobic composting (FMCAC) systems and a conventional aerobic composting system were investigated. The micro-positive pressure in each FMCAC system altered the composting microenvironment, significantly increased the oxygen uptake rates of microbes (p < 0.05), and increased the abundance of cellulose- and hemicellulose-degrading microorganisms. Bacteria and fungi together influenced the conversion between carbon and nitrogen forms. FMCAC made the systems less anaerobic and decreased CH₄ production and emissions by 22.16 %-23.37 % and N₂O production and emissions by 41.34 %-45.37 % but increased organic matter degradation and NH₃ production and emissions by 16.91 %-90.13 %. FMCAC decreased carbon losses, nitrogen losses, and the global warming potential by 7.97 %-11.24 %, 15.43 %-34.00 %, and 39.45 %-42.16 %, respectively. The functional membrane properties (pore size distribution and air permeability) affected fermentation process and gaseous emissions. A comprehensive assessment indicated that FMCAC has excellent prospects for application.

Exploring the mechanism associated with methane emissions during composting: Inoculation with lignocellulose-degrading microorganisms

Inoculation with microorganisms is an effective strategy for improving traditional composting processes. This study explored the effects of inoculation with lignocellulose-degrading microorganisms (LDM) on the degradation of organic matter (OM), methane (CH₄) emissions, and the microbial community (bacteria and methanogens) during composting. The results showed that LDM accelerated the degradation of OM (including the lignocellulose fraction) and increased the CH₄ releases in the later thermophilic and cooling stages during composting. At the ending of composting, LDM increased the CH₄ emissions by 38.6% compared with the control. Moreover, LDM significantly increased the abundances of members of the bacterial and methanogenic community during the later thermophilic period (P < 0.05). In addition, LDM promoted the growth and activity of major bacterial genera (e.g., Ureibacillus) with the ability to degrade macromolecular OM, as well as affecting key methanogens (e.g., Methanocorpusculum) in the composting system. Network analysis and variance partitioning analysis indicated that OM and temperature were the main factors that affected the bacterial and methanogen community structures. Structural equation modeling demonstrated that the higher CH₄ emissions under LDM were related to the growth of methanogens, which was facilitated by the anaerobic environment produced by large amounts of CO₂. Thus, aerobic conditions should be improved during the end of the thermophilic and cooling composting period when inoculating with lignocellulose-degrading microorganisms in order to reduce CH₄ emissions.

Effects of 3D-printed bulking agent on microbial community succession and carbohydrate-active enzymes genes during swine manure composting

The bulking agent plays an important role in aerobic composting, but their shape, porosity, and homogeneity need to be optimized. In the present work, a bulking agent with a uniform shape was prepared by 3D printing to explore its influence on physicochemical parameters, microbial community succession, and gene abundance of carbohydrate-active enzymes (CAZymes) in swine manure aerobic composting. The results showed that adding 3D-printed bulking agents can increase maximum temperature, prolong the thermophilic period, and improve the degradation rate of volatile solids, which was attributed to ameliorative air permeability by the porous 3D-printed bulking agent. The abundances of some pathogenic bacteria decreased and CAZymes genes increased respectively in response to the addition of the 3D-printed bulking agent, implying it has a certain positive effect on improving the safety of compost products and promoting the degradation of organic matter. In summary, the 3D-printed bulking agent has good application potential in laboratory-scale aerobic composting.

Membrane-covered composting significantly decreases methane emissions and microbial pathogens: Insight into the succession of bacterial and fungal communities

In this study, the effects of semipermeable membrane-covered on methane emissions and potential pathogens during industrial-scale composting of the solid fraction of dairy manure were investigated. The results showed that the oxygen concentration in the membrane-covered group (CT) was maintained above 10 %, and the cumulative methane emission in CT was >99 % lower than that in the control group (CK). Microbial analysis showed that the bacterial genus Thermus and the fungal genus Mycothermus were dominant in CT, and the richness and diversity of the bacterial community were greater than those of the fungal community. At the end of the composting, the relative abundance of potential bacterial pathogens in CT was 32.59 % lower than that in CK, and the relative abundance of potential fungal pathogens in each group was <2 %. Structural equation models revealed that oxygen concentration was a major factor influencing the bacterial diversity in CT, and the increase of oxygen concentration could limit methane emissions by inhibiting the growth of anaerobic bacteria. Therefore, membrane-covered composting could effectively improve compost safety and reduce methane emissions by regulating microbial community structure.

Micro-aerobic conditions based on membrane-covered improves the quality of compost products: Insights into fungal community evolution and dissolved organic matter characteristics

This study investigated the effects of micro-aerobic conditions on fungal community succession and dissolved organic matter transformation during dairy manure membrane-covered composting. The results showed that lignocellulose degradation in the micro-aerobic composting group (AC: oxygen concentration < 5 %) was slower than that in the static composting group (SC: oxygen concentration < 1 %), but the dissolved organic carbon in AC was greatly increased. The degree of aromatic polymerization was higher in AC than in SC. But the carboxyl carbon and alcohol/ether biodegradations were faster in SC than in AC, which promoted carbon dioxide and methane emissions, respectively. The relative abundances of pathogenic and dung saprotrophic fungi in AC were 44.6 % and 10.59 % lower than those in SC on day 30, respectively. Moreover, the relative abundance of soil saprotrophs increased by 5.18 % after micro-aerobic composting. Therefore, micro-aerobic conditions improved the quality of compost products by influencing fungal community evolution and dissolved organic matter transformation.

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.

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.

Effects of functional-membrane covering technique on nitrogen succession during aerobic composting: Metabolic pathways, functional enzymes, and functional genes

This study investigated and assessed the effect of the functional-membrane covering technique (FMCT) on nitrogen succession during aerobic composting. By comparative experiments involving high-throughput sequencing and qPCR, nitrogen metabolism (including the ko00910 pathway and functional enzyme and gene abundances) was analyzed, and the nitrogen succession mechanism was identified. The FMCT created a micro-positive pressure, improved the aerobic conditions, and increased the oxygen utilization rate and temperature. This strongly affected the nitrogen metabolism pathway and down-regulated the nitrifying and denitrifying bacteria abundances. The FMCT up-regulated the relative abundance of glutamate dehydrogenase and down-regulated the absolute abundances of AOB and nxrA. This and the high temperature increased NH₃ emissions by 13.78%-73.37%. The FMCT down-regulated the abundances of denitrifying gene groups (nirS + nirK)/nosZ and nitric oxide reductase associated with N₂O emissions and decreased N₂O emissions by 16.44%-41.15%. The results improve the understanding of the mechanism involved in nitrogen succession using the FMCT.

Exploring the microbial mechanism of reducing methanogenesis during dairy manure membrane-covered aerobic composting at industrial scale

In this study, the microbial mechanism of reducing methanogenesis during membrane-covered aerobic composting from solid dairy manure was investigated. An industrial-scale experiment was carried out to compare a static composting group (SC) and a forced aeration composting group (AC) with a semipermeable membrane-covered composting group (MC + AC). The results showed that the semipermeable membrane-covered could improve the oxygen utilization rate and inhibit the anaerobic bacterial genus Hydrogenispora and archaea order Methanobacteriales. During the membrane-covered period, the acetoclastic methanogenesis module in MC + AC, AC and SC decreased by 0.58%, 0.05% and 0.04%, respectively, and the cdhC gene in the acetoclastic pathway was found to be decreased by 65.51% only in MC + AC. Changes in methane metabolism pathways resulted in a 27.48% lower average methane concentration in MC + AC than in SC. Therefore, the semipermeable membrane-covered strategy can effectively reduce methane production during dairy manure aerobic composting by restricting the methanogenesis of the acetoclastic pathway.

Molecular characterization of the composition and transformation of dissolved organic matter during the semi-permeable membrane covered hyperthermophilic composting

Current knowledge of dissolved organic matter (DOM) in semi-permeable membrane-covered thermophilic compost (smHTC) is limited. Therefore, this study provided a comprehensive characterization of composition and transformation of DOM in smHTC using multiple spectroscopic methods and ultrahigh resolution mass spectrometry. The results showed that the values of SUVA₂₈₀, SUVA₂₅₄, A_240-400 (0.042, 0.048, 34.193) in smHTC were higher than those of conventional thermophilic composting (cTC) (0.030, 0.037, 18.348), and the increment of P_V,n in smHTC were 2.4 times higher than that of cTC. These results suggested that smHTC accelerated the humification process by promoting the degradation of labile DOM and the production of humus-like substances. Mass spectrometry further confirmed that the DOM of smHTC possessed higher degree of aromatization and humification, based on the lower H/C (1.14), higher aromaticity index (0.34) and double bond equivalence (10.36). Additionally, smHTC increased the proportion of carboxyl-rich, unsaturated and aromatic compounds, and simultaneously improved the degradation of aliphatic/proteins, lipids, carbohydrates, along with even some refractory substances such as CHO subcategory (24.1%), especially lignin-like structures (14.8%). This investigation provided molecular insights into the composition and transformations of DOM in smHTC, and extended the current molecular mechanisms of humification in composting.

Influence of microbial inoculants on co-composting of lignocellulosic crop residues with farm animal manure: A review

The rapidly developing agro-industry generates huge amounts of lignocellulosic crop residues and animal manure worldwide. Although co-composting represents a promising and cost-effective method to treat various agricultural wastes simultaneously, poor composting efficiency prolongs total completion time and deteriorates the quality of the final product. However, supplementation of the feedstock with beneficial microorganisms can mitigate these negative effects by facilitating the decomposition of recalcitrant materials, enhancing microbial enzyme activity, and promoting maturation and humus formation during the composting process. Nevertheless, the influence of microbial inoculation may vary greatly depending on certain factors, such as start-up parameters, structure of the feedstock, time of inoculation, and composition of the microbial cultures used. The purpose of this contribution is to review recent developments in co-composting procedures involving different lignocellulosic crop residues and farm animal manure combined with microbial inoculation strategies. To evaluate the effectiveness of microbial additives, the results reported in a large number of peer-reviewed articles were compared in terms of composting process parameters (i.e., temperature, microbial activity, total organic carbon and nitrogen contents, decomposition rate of lignocellulose fractions, etc.) and compost characteristics (humification, C/N ratio, macronutrient content, and germination index). Most studies confirmed that the use of microbial amendments in the co-composting process is an efficient way to facilitate biodegradation and improve the sustainable management of agricultural wastes. Overall, this review paper provides insights into various inoculation techniques, identifies the limitations and current challenges of co-composting, especially with microbial inoculation, and recommends areas for further research in this field.

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.

Evolution of physicochemical properties and bacterial community in aerobic composting of swine manure based on a patent compost tray

The objective of this study was to explore the changes in physicochemical properties and bacterial community during swine manure composting with a new compost tray (CT). The results showed that the organic matter (OM), moisture content (MC), and C/N decreased. The total Kjeldahl nitrogen (TKN), P₂O₅, K₂O and humic acids (HAs) contents of the compost increased. The properties of the final compost product comply with the requirements of regulation except for the moisture according to NY/T 525-2012. Firmicutes, Actinobacteria, Proteobacteria and Bacteroidetes were the major phyla during the composting. Genus Terrisporobacter played a key role in degrading organic (OM). The content of K₂O was main factors driving the succession of bacterial communities. These findings shed some novel lights into the dynamic changes of physicochemical propertied and their impact on bacterial community in a composting process.

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.

Hyperthermophilic composting significantly decreases methane emissions: Insights into the microbial mechanism

Methane (CH₄) emissions from thermophilic composting (TC) are a substantial contributor to climate change. Hyperthermophilic composting (HTC) can influence CH₄-related microbial communities at temperatures up to 80 °C, and thus impact the CH₄ emissions during composting. This work investigated CH₄ emissions in sludge-derived HTC, and explored microbial community succession with quantitative PCR and high-throughput sequencing. Results demonstrated that HTC decreased CH₄ emissions by 52.5% compared with TC. In HTC, the CH₄ production potential and CH₄ oxidation potential were nearly 40% and 64.1% lower than that of TC, respectively. There was a reduction in the quantity of mcrA (3.7 × 10⁸ to 0 g^-1 TS) in HTC, which was more significant than the reduction in pmoA (2.0 × 10⁵ to 2.1 × 10⁴ g^-1 TS), and thus lead to reduce CH₄ emissions. It was found that the abundance of most methanogens and methanotrophs was inhibited in the hyperthermal environment, with a decline in Methanosarcina, Methanosaeta and Methanobrevibacter potentially being responsible for reducing the CH₄ emissions in HTC. This work provides important insight into mitigating CH₄ emissions in composting.

Mitigation of carbon and nitrogen losses during pig manure composting: A meta-analysis

Composting is a reliable way to recycle manure for use on croplands in sustainable agriculture. Poor management of the composting process can result in a decrease in the final compost quality and negative environmental impacts. Optimization technologies during composting have varied effects on the mitigation of carbon (C) and nitrogen (N) losses. To determine the feasibility and effectiveness of mitigation options, a meta-analysis was performed based on 68 studies in which C and/or N losses were investigated during pig manure composting. The results indicated that 48.7% of the total C (TC) was lost with 34.8% as CO₂-C and 0.9% as CH₄-C, and 27.5% of the total N (TN) was lost with 17.1% as NH₃-N and 1.5% as N₂O-N. The composting method and bulking agent type obviously influenced the C and N losses. CO₂-C and CH₄-C emission was significantly influenced by the initial C/N ratio and moisture, respectively. At the same time, NH₃-N and N₂O-N emissions were remarkably affected by the initial pH and composting duration, respectively. The results of the meta-analysis showed that TC and TN losses were reduced by 12.4% and 27.5%, respectively. Controlling feedstock, including the C/N ratio and moisture, could be regarded as N conservation technology. Controlling aeration, including turning frequency and ventilation rate, would be reliable in reducing greenhouse gas emissions. Applying additives, especially biochar and superphosphate, was found to be an effective method for synergistically mitigating C and N losses. Therefore, the production of high-quality compost products and minimization of environmental pollution will be achieved by a combination of adjusting the initial substrate properties, controlling the composting process conditions and applying additives.

Effects of semi-permeable membrane covering coupled with intermittent aeration on gas emissions during aerobic composting from the solid fraction of dairy manure at industrial scale

In this study, the effects of covering the compost pile with a semi-permeable membrane in combination with intermittent aeration on the gas emissions during aerobic composting from the solid fraction of dairy manure at industrial scale were investigated. A large-scale composting experiment was carried out to compare a membrane-covered (CT) group with a control (CK) group. The results indicated that the CT group could maintain a suitable aerobic and positive micro-pressure environment. The carbon dioxide, methane, nitrous oxide, and ammonia emissions outside the membrane during the aeration interval were reduced by 64.23%, 70.07%, 54.87%, and 11.32%, respectively, compared with that inside the membrane. It was also determined that the methane and nitrous oxide emissions from the CT group were reduced by 99.89% and 60.48% relative to the CK group, confirming that the combined process represented a novel strategy for reducing gas emissions during dairy manure composting.

Nitrogen transformation and dynamic changes in related functional genes during functional-membrane covered aerobic composting

The effects of functional membrane covering (FMC) on nitrogen transformation and related functional genes during aerobic composting were investigated by performing a comparable experiment. The FMC increased the pile temperature, promoted compost maturity, and decreased nitrogen loss. The FMC reduced NH₃ and N₂O emissions by 7.34% and 26.27%, respectively. The water film and the micro-positive pressure environment under the membrane effectively prevented NH₃ escaping. The FMC up-regulated the amoA gene copy number (promoting NH₃/NH₄⁺ oxidation). The reduction of N₂O emission by the FMC was mainly related to denitrifying genes (nirK, nirS, and nosZ). The FMC down-regulated the nirK and nirS gene copy numbers, but up-regulated the nosZ gene copy number. Pearson correlation analysis indicated that the functional membrane characteristics and differences between the composting pile environments caused by the FMC significantly affected the nitrogen forms and the related functional genes. The FMC strongly decreased nitrogen emissions and therefore conserved nitrogen.

Decreased Methane Emissions Associated with Methanogenic and Methanotrophic Communities in a Pig Manure Windrow Composting System under Calcium Superphosphate Amendment

With the rapid growth of livestock breeding, manure composting has evolved to be an important source of atmospheric methane (CH4) which accelerates global warming. Calcium superphosphate (CaSSP), as a commonly used fertilizer, was proposed to be effective in reducing CH4 emissions from manure composting, but the intrinsic biological mechanism remains unknown. Methanogens and methanotrophs both play a key role in mediating CH4 fluxes, therefore we hypothesized that the CaSSP-mediated reduction in CH4 emissions was attributed to the shift of methanogens and methanotrophs, which was regulated by physicochemical parameter changes. To test this hypothesis, a 60-day pig manure windrow composting experiment was conducted to investigate the response of CH4 emissions to CaSSP amendment, with a close linkage to methanogenic and methanotrophic communities. Results showed that CaSSP amendment significantly reduced CH4 emissions by 49.5% compared with the control over the whole composting period. The decreased mcrA gene (encodes the α-subunit of methyl-coenzyme M reductase) abundance in response to CaSSP amendment suggested that the CH4 emissions were reduced primarily due to the suppressed microbial CH4 production. Illumina MiSeq sequencing analysis showed that the overall distribution pattern of methanogenic and methanotrophic communities were significantly affected by CaSSP amendment. Particularly, the relative abundance of Methanosarcina that is known to be a dominant group for CH4 production, significantly decreased by up to 25.3% accompanied with CaSSP addition. Only Type I methanotrophs was detected in our study and Methylocaldum was the dominant methanotrophs in this composting system; in detail, CaSSP amendment increased the relative abundance of OTUs belong to Methylocaldum and Methylobacter. Moreover, the increased SO42- concentration and decreased pH acted as two key factors influencing the methanogenic and methanotrophic composition, with the former has a negative effect on methanogenesis growth and can later promote CH4 oxidation at a low level. This study deepens our understanding of the interaction between abiotic factors, function microbiota and greenhouse gas (GHG) emissions, as well as provides implication for practically reducing composting GHG emissions.

Can white clover facilitate apple orchard residue composting?

Aiming to assess the efficiency of white clove (WC) as an alternative nitrogen source for composting and to facilitate the utilization of orchard waste, WC as compared with chicken manure (CM) was aerobically composted with apple tree leaves (ATL) in initial C/N ratios of 25(R25), 30(R30) and 35(R35). The results show that WC facilitated the rapid and harmless treatment of ATL with the compost temperature above 55°C for more than 3 days. After composting, for all final products, organic matter content was 69.9%-72.9%, electrical conductivity (EC) 1.48-2.31 ms cm^-1, germination index (GI) more than 80% and C/N ratios less than 20. Among all treatments, the product from R30 was most nutrient-rich. Compared with CM, WC facilitated the harmless treatment of ATL and required less time for high quality compost production. It is concluded that WC is an excellent replacement for animal manure as a nitrogen source in field composting of orchard waste in areas with limited transportation. WC and ATL can produce high quality organic fertilizer and initial C/N ratio of 30 is recommended.

A Review of Composting Process Models of Organic Solid Waste with a Focus on the Fates of C, N, P, and K

To foster a circular economy in line with compost quality assessment, a deep understanding of the fates of nutrients and carbon in the composting process is essential to achieve the co-benefits of value-added and environmentally friendly objectives. This paper is a review aiming to fill in the knowledge gap about the composting process. Firstly, a systematic screening search and a descriptive analysis were conducted on composting models involving the fates of Carbon (C), Nitrogen (N), Phosphorus (P) and Potassium (K) over the past decade, followed by the development of a checklist to define the gap between the existing models and target models. A review of 22 models in total led to the results that the mainstream models involved the fates of C and N, while only a few models involved P and K as target variables. Most of the models described the laboratory-scale composting process. Mechanism-derived models were relatively complex; however, the application of the fractionation of substrates could contribute to reducing the complexity. Alternatively, data-driven models can help us obtain more accurate predictions and involve the fates of more nutrients, depending on the data volume. Finally, the perspective of developing composting models for the fates of C, N, P, and K was proposed.

Microbial mechanisms related to the effects of bamboo charcoal and bamboo vinegar on the degradation of organic matter and methane emissions during composting

In this study, functional microbial sequencing, quantitative PCR, and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) were employed to understand the microbial mechanisms related to the effects of bamboo charcoal (BC) and bamboo vinegar (BV) on the degradation of organic matter (OM) and methane (CH₄) emissions during composting. BC + BV resulted in the highest degradation of OM. BV was most effective treatment in controlling CH₄ emissions and it significantly reduced the abundance of the mcrA gene. Methanobrevibacter, Methanosarcina, and Methanocorpusculum were closely related to CH₄ emissions during the thermophilic composting period. PICRUSt analysis showed that BC and/or BV enhanced the metabolism associated with OM degradation and reduced CH₄ metabolism. Structural equation modeling indicated that BC + BV strongly promoted the metabolic activity of microorganisms, which had a positive effect on CH₄ emissions. Together these results suggest that BC + BV may be a suitable composting strategy if the aerobic conditions can be effectively improved during the thermophilic composting period.

Enhanced removal of antibiotic resistance genes and mobile genetic elements during sewage sludge composting covered with a semi-permeable membrane

Transmission of antibiotic resistance genes (ARGs) via air media, such as particulate matter, has been intensively investigated due to human exposure through inhalation. However, whether particulate matter originating from the atmospheric environment of composting plants can impact ARG abundance during composting is unknown. Here, we investigated the effects of the atmospheric environment of composting plants on ARG abundance during sewage sludge composting using semi-permeable membrane-covered thermophilic composting (smTC) and conventional thermophilic composting (cTC). After smTC treatment, the total abundances of ARGs and mobile genetic elements (MGEs) decreased by 42.1 % and 38.1 % compared with those of the initial phase, respectively, but they increased by 4.5- and 1.6-fold after cTC, respectively. This result suggested that smTC was more efficient at decreasing ARGs and MGEs than cTC, mainly due to a significant reduction in bacterial contamination from the atmospheric environment of composting plants that accelerated the resurgence of ARGs and MGEs. Furthermore, culture experiments demonstrated that the abundance and diversity of antibiotic-resistant bacteria during the mature phase of smTC were also significantly (P <  0.05) lower than those in the cTC treatment. Thus, covering composting with a semi-permeable membrane could decrease the risk of ARGs spreading.

Exploring the mechanisms of organic matter degradation and methane emission during sewage sludge composting with added vesuvianite: Insights into the prediction of microbial metabolic function and enzymatic activity

Effect mechanisms of organic matter (OM) degradation and methane (CH₄) emission during sewage sludge (SS) composting with added vesuvianite (V) were studied by high-throughput sequencing (HTS) and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt). Results show that the addition of V accelerated the OM degradation and decreased the cumulative CH₄ emissions by 33.6% relative to the control. In addition, V significantly decreased the mcrA gene abundance and the methanogen community richness at the genus level. PICRUSt also indicated that V strengthens the microbial metabolic function and enzymatic activity related to OM degradation, and reduced the enzymatic activity related to CH₄ production. Methanogens community variation analysis proved the ratio of carbon and nitrogen and moisture content are the significant variables affecting CH₄ emissions. Thus, optimizing the ratio of carbon and nitrogen and moisture content will decrease CH₄ emission during SS composting.