N2O emission factors of full-scale animal manure windrow composting in cold and warm seasons

Insight into N2O emission and denitrifier communities under different aeration intensities in composting of cattle manure from perspective of multi-factor interaction analysis

Nitrous oxide (N2O) emission from composting is a significant contributor to greenhouse effect and ozone depletion, which poses a threat to environment. To address the challenge of mitigating N2O emission during composting, this study investigated the response of N2O emission and denitrifier communities (detected by metagenome sequencing) to aeration intensities of 6 L/min (C6), 12 L/min (C12), and 18 L/min (C18) in cattle manure composting using multi-factor interaction analysis. Results showed that N2O emission occurred mainly at mesophilic phase. Cumulative N2O emission (QN2O, 9.79 mg·kg-1 DW) and total nitrogen loss (TN loss, 16.40 %) in C12 composting treatment were significantly lower than those in the other two treatments. The lower activity of denitrifying enzymes and the more complex and balanced network of denitrifiers and environmental factors might be responsible for the lower N2O emission. Denitrification was confirmed to be the major pathway for N2O production. Moisture content (MC) and Luteimonas were the key factors affecting N2O emission, and nosZ-carrying denitrifier played a significant role in reducing N2O emission. Although relative abundance of nirS was lower than that of nirK significantly (P < 0.05), nirS was the key gene influencing N2O emission. Community composition of denitrifier varied significantly with different aeration treatments (R2 = 0.931, P = 0.001), and Achromobacter was unique to C12 at mesophilic phase. Physicochemical factors had higher effect on QN2O, whereas denitrifying genes, enzymes and NOX- had lower effect on QN2O in C12. The complex relationship between N2O emission and the related factors could be explained by multi-factor interaction analysis more comprehensively. This study provided a novel understanding of mechanism of N2O emission regulated by aeration intensity in composting.

Material flow analysis and global warming potential assessment of an industrial insect-based bioconversion plant using housefly larvae

The significant increase in the demand for biomass waste treatment after garbage classification has led to housefly larvae treatment becoming an attractive treatment option. It can provide a source of protein while treating biomass waste, which means that nutrients can be returned to the natural food chain. However, the performance of this technology in terms of its environmental impacts is still unclear, particularly with regards to global warming potential (GWP).This study used a life cycle assessment (LCA) approach to assess a housefly larvae treatment plant with a treatment capacity of 50 tons of biomass waste per day. The LCA results showed that the 95% confidence intervals for the GWP in summer and winter were determined to be 24.46-32.81 kg CO2 equivalent (CO2-eq)/ton biomass waste and 5.37-10.08 kg CO2-eq/ton biomass waste, respectively. The greater GWP value in summer is due to the longer ventilation time and higher ventilation intensity in summer, which consumes more power. The main GWP contributions are from (1) electricity needs (accounting for 78.6% of emissions in summer and 70.2% in winter) and (2) product substitution by mature housefly larvae and compost (both summer and winter accounting for 96.8% of carbon reduction).

Trends in the management of organic swine farm waste by composting: A systematic review

Pig farming contributes to the economic development of nations and supplies human food demand; however, it generates a large amount of organic waste which, if not managed properly, becomes a risk to the environment and human and animal health. Considering the relevance of composting and its usefulness for the use of waste, this study aimed to determine the global trends in the management of composting manure, mortality and other organic waste produced on pig farms over the last five years (2017-2022). Systematic search involved four databases: ISI Web of Science, Scopus, Ebsco and Scielo. Of the total findings, 56 articles were included in the review, further classified into 14 categories for their respective analysis: co-substrates/additives, microbial communities, antibiotic resistance, heavy metals, polycyclic aromatic hydrocarbons, microbiological/parasitological quality, phytopathogens, nitrogen transformation, bioinoculants, comparison/combination with other waste management techniques, factors affecting composting, swine mortality and plant growth promotion/phytotoxicity. The review exemplified the importance of swine mortality composting as an alternative for organic matter management in pig farms, considering that the process also includes manure, vegetable waste and wood chips, among others. Controlled factors throughout the process are a requirement to obtain a stable product with physicochemical and microbiological quality that complies with national and international regulations and that will be useful and safe for application on crops, ensuring environmental, animal, and human health.

Agriculture-Induced N2O Emissions and Reduction Strategies in China

Greenhouse gases are one of the most important factors in climate change, their emissions reduction is a global problem. Clarifying the spatial patterns of N2O, as an important component of greenhouse gases, it is of great significance. Based on the planting and breeding data of China from 2000 to 2019, this paper measures the N2O emissions of agricultural systems, and uses kernel density to explore the spatial distribution differences between the eight major economic zones. Finally, the proposed emissions reduction countermeasures are provided. The research results show that the N2O emissions of China's agricultural system showed a trend of increasing first and then decreasing, and in 2019, the national N2O emissions were 710,300 tons, agricultural land emissions and animal husbandry emissions were the main sources of N2O emissions. The difference in N2O emissions by province was significant, the concentration trend was more prominent, and the differences of N2O emissions between provinces and regions were diverse. In order to achieve the reduction in N2O emissions, it is necessary to carry out low-carbon production of staple grains for different parts and economic zones, and focusing on low-carbon production in the Central Part and the West Part, as well as the Northeast and the Greater Southwest zones, is essential.

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.

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.

Greenhouse Gas Emissions From Biofilters for Composting Exhaust Ammonia Removal

Emissions of odorous compounds, such as ammonia (NH₃), from composting have negative agronomic and environmental impacts. A biofilter is widely used for NH₃ removal, with one of its potential detrimental by-products being nitrous oxide (N₂O), which is a higher warming potential greenhouse gas (GHG). The aim of the study was to evaluate the effect of empty bed retention time (EBRT) on GHG emissions from biofilters for removing NH₃ from composting. Composting experimental trials lasted 6 weeks, and composting materials were mixtures of dead pigs and manure. Three groups of biofilters with 1.2 m-height, 0.3 m-inner diameter, and 1.0 m media depth were conducted with EBRT of 30, 60, and 100s, respectively. Each treatment was performed in triplicate, and the gas was monitored using the dynamic emission vessel method. The Spearman’s correlation analysis showed a significantly positive correlation between inlet concentrations (ICs) of NH₃ and increased N₂O concentrations: ρ = 0.707, 0.762, and 0.607 with p ≤ 0.0001 for biofilters with EBRT of 30, 60, and 100s, respectively. The fraction of NH₃-N denitrified into N₂O-N in biofilters with EBRT of 60 and 100s was higher than that with EBRT of 30s. The total global warming potential (GWP) increased by 126%, 162%, and 144% for biofilters with EBRT of 30, 60, and 100s, respectively. These results indicated that biofilters with longer EBRT will lead to higher GWP production. Future research on odorous mitigation for composting with biofilters should focus more on greenhouse gas emissions.

Policy-enabled stabilization of nitrous oxide emissions from livestock production in China over 1978-2017

Mitigating livestock-related nitrous oxide (N₂O) emissions is key for China to meet its 2060 carbon neutrality target. Here we present a comprehensive analysis of the magnitude, spatiotemporal variation and drivers of Chinese livestock N₂O emissions from 1978 to 2017. We developed scenarios to explore emissions mitigation potential and associated marginal abatement costs and social benefits. The average growth rate of China's livestock N₂O emissions increased by 4.6% per year through 2006, falling sharply over 2007-2015 and gradually declining in 2017 due to a slowdown in population and meat-consumption growth rates. We estimate the technical mitigation potential of livestock N₂O emissions in 2030 to be 7-21% (or 23.1-70.9 Gg N₂O), with implementation costs of US$5.5 billion to US$6.0 billion. Priority regions for intervention were identified in the North China Plain, Northeast Plain and Lianghu Plain. Among mitigation opportunities, anaerobic digestion offers the greatest social benefit, while low crude protein feed is the most cost-effective option.

Moisture-Induced Pattern of Gases and Physicochemical Indices in Corn Straw and Cow Manure Composting

This study investigated the altering effect of moisture on the emission pattern of gases and the evolutionary dynamics of physicochemical indices in corn straw and cow manure composting. Exploring this effect was reasonable to unravel the use of moisture as a cheap alternative to control gaseous emissions and improve the final properties of compost. The nutrient dynamics of the compost showed 21.6% losses in total organic carbon content, with a 33.3% increase in total nitrogen content at the end of composting. All the gases (CH4, CO2, N2O and NH3) yielded a common emission pattern despite the differences in moisture content. Except for CH4, the peak and stable emission periods of all the gases were observed on the 5th day (thermophilic phase) and after the 27th day (late mesophilic phase) of composting, respectively. Emission reductions of 89%, 91%, 95% and 100% were recorded for CH4, CO2, N2O and NH3, respectively, during the late mesophilic phase of composting. From the study, the 65% moisture content was efficient in reducing the loss rate of the gasses and nutrient contents of the compost. This study would enable farmers to channel organic residues generated into compost while minimizing pollution and nutrient losses associated with the composting process.

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.

Effects of urease inhibitors on enzymatic activities and fungal communities during the biosolids composting

This study evaluated the influences of urease inhibitors (UIs) on nitrogen conversion, enzyme activities, and fungal communities during aerobic composting. Results showed that UI addition reduced NH₃ emissions by 22.2% and 21.5% and increased the total nitrogen (TN) content by 9.7% and 14.3% for the U1 (0.5% UI of the dry weight of the mixture) and U2 (1% UI of the dry weight of the mixture) treatments, respectively. The addition of UI inhibited the enzyme activity during thermophilic stage while increased enzyme activity during the cool and maturity stages. Ascomycota, Basidiomycota and unclassified fungi were the main phyla, and Ascomycota increased significantly during the maturity period. Network analysis showed that Aspergillus, Penicillium, Trichoderma, Talaromyces, Peseudeurotium, and Exophiala were the main “connecting” genera. The redundancy analysis (RDA) showed that the fungal community was mainly influenced by temperature, DOC, pH, and urease. The results suggested that UI was an effective additive for nitrogen conservation and the increase of enzyme activity reduce nitrogen loss and promote enzyme activity during biosolids composting.

Adding UI was effective for nitrogen conservation and the increase of enzyme activity during biosolid composting.