Combining slow-release fertilizer and plastic film mulching reduced the carbon footprint and enhanced maize yield on the Loess Plateau.

Agricultural practices significantly contribute to greenhouse gas (GHG) emissions, necessitating cleaner production technologies to reduce environmental pressure and achieve sustainable maize production. Plastic film mulching is commonly used in the Loess Plateau region. Incorporating slow-release fertilizers as a replacement for urea within this practice can reduce nitrogen losses and enhance crop productivity. Combining these techniques represents a novel agricultural approach in semi-arid areas. However, the impact of this integration on soil carbon storage (SOCS), carbon footprint (CF), and economic benefits has received limited research attention. Therefore, we conducted an eight-year study (2015-2022) in the semi-arid northwestern region to quantify the effects of four treatments [urea supplied without plastic film mulching (CK-U), slow-release fertilizer supplied without plastic film mulching (CK-S), urea supplied with plastic film mulching (PM-U), and slow-release fertilizer supplied with plastic film mulching (PM-S)] on soil fertility, economic and environmental benefits. The results revealed that nitrogen fertilizer was the primary contributor to total GHG emissions (≥71.97%). Compared to other treatments, PM-S increased average grain yield by 12.01%-37.89%, water use efficiency by 9.19%-23.33%, nitrogen accumulation by 27.07%-66.19%, and net return by 6.21%-29.57%. Furthermore, PM-S decreased CF by 12.87%-44.31% and CF per net return by 14.25%-41.16%. After eight years, PM-S increased SOCS (0-40 cm) by 2.46%, while PM-U decreased it by 7.09%. These findings highlight the positive effects of PM-S on surface soil fertility, economic gains, and environmental benefits in spring maize production on the Loess Plateau, underscoring its potential for widespread adoption and application.

Impacts of the global food system on terrestrial biodiversity from land use and climate change.

The global food system is a key driver of land-use and climate change which in turn drive biodiversity change. Developing sustainable food systems is therefore critical to reversing biodiversity loss. We use the multi-regional input-output model EXIOBASE to estimate the biodiversity impacts embedded within the global food system in 2011. Using models that capture regional variation in the sensitivity of biodiversity both to land use and climate change, we calculate the land-driven and greenhouse gas-driven footprints of food using two metrics of biodiversity: local species richness and rarity-weighted species richness. We show that the footprint of land area underestimates biodiversity impact in more species-rich regions and that our metric of rarity-weighted richness places a greater emphasis on biodiversity costs in Central and South America. We find that methane emissions are responsible for 70% of the overall greenhouse gas-driven biodiversity footprint and that, in several regions, emissions from a single year's food production are associated with global biodiversity loss equivalent to 2% or more of that region's total land-driven biodiversity loss. The measures we present are relatively simple to calculate and could be incorporated into decision-making and environmental impact assessments by governments and businesses.

Estimation of methane greenhouse gas emissions from livestock in Egypt during 1989 to 2021.

This study investigates methane emissions from the livestock sector, representing by enteric fermentation and manure management, in Egypt from 1989 to 2021, focusing on spatial and temporal variations at the governorate level. Utilizing IPCC guidelines and emission factors, methane emissions were estimated for dairy and non-dairy cattle, buffalo, sheep and goat, poultry, and other livestock categories. Results reveal fluctuating emission patterns over the study period, with notable declines in certain governorates such as Kafr El-Sheikh and Red Sea, attributed to reductions in livestock populations. However, increasing trends were observed overall, driven by population growth in other regions. Hotspots of methane emissions were identified in delta governorates like Behera and Sharkia, as well as agriculturally rich regions including Menia and Suhag. While livestock populations varied between regions, factors such as water availability, climatic conditions, and farming practices influenced distribution. Notably, cluster analysis did not reveal regional clustering among governorates, suggesting emissions changes were not dependent on specific geographic or climatic boundaries. Manure management accounted for only 5-6% of total emissions, with emissions at their lowest in the last three years due to population declines. Despite the highest livestock populations being sheep and goats, emissions from enteric fermentation and manure management were highest from buffalo and cattle. This study underscores the importance of accurate data collection and adherence to IPCC recommendations for estimating GHG emissions, enabling the development of targeted mitigation strategies to address climate change challenges in the livestock sector.

Plant diversity decreases greenhouse gas emissions by increasing soil and plant carbon storage in terrestrial ecosystems.

The decline in global plant diversity has raised concerns about its implications for carbon fixation and global greenhouse gas emissions (GGE), including carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). Therefore, we conducted a comprehensive meta-analysis of 2103 paired observations, examining GGE, soil organic carbon (SOC) and plant carbon in plant mixtures and monocultures. Our findings indicate that plant mixtures decrease soil N2O emissions by 21.4% compared to monocultures. No significant differences occurred between mixtures and monocultures for soil CO2 emissions, CH4 emissions or CH4 uptake. Plant mixtures exhibit higher SOC and plant carbon storage than monocultures. After 10 years of vegetation development, a 40% reduction in species richness decreases SOC content and plant carbon storage by 12.3% and 58.7% respectively. These findings offer insights into the intricate connections between plant diversity, soil and plant carbon storage and GGE-a critical but previously unexamined aspect of biodiversity-ecosystem functioning.

Greenhouse gas emissions in the Indian agriculture sector and mitigation by best management practices and smart farming technologies-a review.

The growing demand for agricultural products, driven by the Green Revolution, has led to a significant increase in food production. However, the demand is surpassing production, making food security a major concern, especially under climatic variation. The Indian agriculture sector is highly vulnerable to extreme rainfall, drought, pests, and diseases in the present climate change scenario. Nonetheless, the key agriculture sub-sectors such as livestock, rice cultivation, and biomass burning also significantly contribute to greenhouse gas (GHG) emissions, a driver of global climate change. Agriculture activities alone account for 10-12% of global GHG emissions. India is an agrarian economy and a hub for global food production, which is met by intensive agricultural inputs leading to the deterioration of natural resources. It further contributes to 14% of the country's total GHG emissions. Identifying the drivers and best mitigation strategies in the sector is thus crucial for rigorous GHG mitigation. Therefore, this review aims to identify and expound the key drivers of GHG emissions in Indian agriculture and present the best strategies available in the existing literature. This will help the scientific community, policymakers, and stakeholders to evaluate the current agricultural practices and uphold the best approach available. We also discussed the socio-economic, and environmental implications to understand the impacts that may arise from intensive agriculture. Finally, we examined the current national climate policies, areas for further research, and policy amendments to help bridge the knowledge gap among researchers, policymakers, and the public in the national interest toward GHG reduction goals.

Maximizing pollutant removal and greenhouse gas emission reduction in vertical flow constructed wetlands: an orthogonal experimental approach.

Owing to the impact of the effluent C/N from the secondary structures of urban domestic wastewater treatment plants, the denitrification efficiency in constructed wetlands (CWs) is not satisfactory, limiting their widespread application in the deep treatment of urban domestic wastewater. To address this issue, we constructed enhanced CWs and conducted orthogonal experiments to investigate the effects of different factors (C/N, fillers, and plants) on the removal of conventional pollutants and the reduction of greenhouse gas (GHG) emission. The experimental results indicated that a C/N of 8, manganese sand, and calamus achieved the best denitrification efficiencies with removal efficiencies of 85.7%, 95.9%, and 88.6% for TN, NH4+-N, and COD, respectively. In terms of GHG emission reduction, this combination resulted in the lowest global warming potential (176.8 mg/m2·day), with N2O and CH4 emissions of 0.53 and 1.25 mg/m2·day, respectively. Characterization of the fillers revealed the formation of small spherical clusters of phosphates on the surfaces of manganese sand and pyrite and iron oxide crystals on the surface of pyrite. Additionally, the surface Mn (II) content of the manganese sand increased by 8.8%, and the Fe (III)/Fe (II) and SO42-/S2- on pyrite increased by 2.05 and 0.26, respectively, compared to pre-experiment levels. High-throughput sequencing indicated the presence of abundant autotrophic denitrifying bacteria (Sulfuriferula, Sulfuritalea, and Thiobacillus) in the CWs, which explains denitrification performance of the enhanced CWs. This study aimed to explore the mechanism of efficient denitrification and GHG emission reduction in the enhanced CWs, providing theoretical guidance for the deep treatment of urban domestic wastewater.

Effect of using households' information and communication technology on CO2 emissions-empirical evidence of the city of Novi Sad.

Globally, the carbon footprint (CF) is constantly increasing, contrasting with the decreasing trend observed for decades in the European Union (EU) countries, where EU guidelines are responsibly followed and outlined in its strategic documents. Information and communication technology (ICT) carbon emissions have historically increased in parallel with global emissions, contributing to continuous increases in ICT's CF over time, even when excluding full life cycle emissions. This study examines the impact of ICT on household electricity consumption, aiming to quantify the potential reduction of greenhouse gas (GHG) emissions through improved household energy efficiency. The methodology includes the data collection on ICT device usage in households within the city of Novi Sad (Republic of Serbia), employing the survey method that queries respondents on device quantities and their usage patterns. This study provides results for decision-makers to recognize concrete benefits from the transition to a circular economy (CE) and low-carbon emissions, which are reflected as benefits for the local community and socio-economic environment.

Changing climatic controls on the greenhouse gas balance of thermokarst bogs during succession after permafrost thaw.

Permafrost thaw in northern peatlands causes collapse of permafrost peat plateaus and thermokarst bog development, with potential impacts on atmospheric greenhouse gas exchange. Here, we measured methane and carbon dioxide fluxes over 3 years (including winters) using static chambers along two permafrost thaw transects in northwestern Canada, spanning young (~30 years since thaw), intermediate and mature thermokarst bogs (~200 years since thaw). Young bogs were wetter, warmer and had more hydrophilic vegetation than mature bogs. Methane emissions increased with wetness and soil temperature (40 cm depth) and modelled annual estimates were greatest in the young bog during the warmest year and lowest in the mature bog during the coolest year (21 and 7 g C-CH4 m-2 year-1, respectively). The dominant control on net ecosystem exchange (NEE) in the mature bog (between +20 and -54 g C-CO2 m-2 year-1) was soil temperature (5 cm), causing net CO2 loss due to higher ecosystem respiration (ER) in warmer years. In contrast, wetness controlled NEE in the young and intermediate bogs (between +55 and -95 g C-CO2 m-2 year-1), where years with periodic inundation at the beginning of the growing season caused greater reduction in gross primary productivity than in ER leading to CO2 loss. Winter fluxes (November-April) represented 16% of annual ER and 38% of annual CH4 emissions. Our study found NEE of thermokarst bogs to be close to neutral and rules out large CO2 losses under current conditions. However, high CH4 emissions after thaw caused a positive net radiative forcing effect. While wet conditions favouring high CH4 emissions only persist for the initial young bog period, we showed that continued climate warming with increased ER, and thus, CO2 losses from the mature bog can cause net positive radiative forcing which would last for centuries after permafrost thaw.

Declining lake ice in response to climate change can impact spending for local communities.

Lake ice is an important socio-economic resource that is threatened by climate change. The cover and duration of lake ice are expected to decline as air temperatures warm in the coming decades, disrupting a previously reliable source of income for many activities dependent on lake ice. The economic consequences of climate-induced lake ice loss remain unexplored, creating a significant research gap. The purpose of this study was to quantify the monetary spending associated with lake ice and how climate change may impact that value. Using a series of General Circulation Models (GCMs), greenhouse gas emissions scenarios, and models for lake ice cover, we predicted changes in lake ice by the end of the 21st century for the Northern Hemisphere. We also synthesized examples of spending associated with lake ice activities and discussed the potential implications expected with declining ice cover. We found that lake ice will decrease in area by 44,000-177,000 km2 and shorten in duration by 13-43 days by 2100. Using 31 examples of revenue from lake ice, we found that lake ice generates spending of over USD 2.04 billion to local communities and economies. We also found that countries predicted to experience the greatest ice loss by the end of the century are those that currently have the largest GDP, highest greenhouse gas emissions, and are most dependent on freshwater withdrawal. Our findings confirm predicted losses in lake ice that are expected because of climate change and quantify some of the potential consequences for local communities. Here we highlight lake ice as another casualty of human-caused climate change that will have profound socio-economic implications.

Impact of three decades of warming, increased nutrient availability, and increased cloudiness on the fluxes of greenhouse gases and biogenic volatile organic compounds in a subarctic tundra heath.

Climate change is exposing subarctic ecosystems to higher temperatures, increased nutrient availability, and increasing cloud cover. In this study, we assessed how these factors affect the fluxes of greenhouse gases (GHGs) (i.e., methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2)), and biogenic volatile organic compounds (BVOCs) in a subarctic mesic heath subjected to 34 years of climate change related manipulations of temperature, nutrient availability, and light. GHGs were sampled from static chambers and gases analyzed with gas chromatograph. BVOCs were measured using the push-pull method and gases analyzed with chromatography-mass spectrometry. The soil temperature and moisture content in the warmed and shaded plots did not differ significantly from that in the controls during GHG and BVOC measurements. Also, the enclosure temperatures during BVOC measurements in the warmed and shaded plots did not differ significantly from temperatures in the controls. Hence, this allowed for assessment of long-term effects of the climate treatment manipulations without interference of temperature and moisture differences at the time of measurements. Warming enhanced CH4 uptake and the emissions of CO2, N2O, and isoprene. Increased nutrient availability increased the emissions of CO2 and N2O but caused no significant changes in the fluxes of CH4 and BVOCs. Shading (simulating increased cloudiness) enhanced CH4 uptake but caused no significant changes in the fluxes of other gases compared to the controls. The results show that climate warming and increased cloudiness will enhance CH4 sink strength of subarctic mesic heath ecosystems, providing negative climate feedback, while climate warming and enhanced nutrient availability will provide positive climate feedback through increased emissions of CO2 and N2O. Climate warming will also indirectly, through vegetation changes, increase the amount of carbon lost as isoprene from subarctic ecosystems.

Assessing carbon tax using a CGE model with firm heterogeneity: An application to Vietnam.

Vietnam's government is considering introducing a carbon market as part of its decarbonization strategy. The carbon tax is an option for the government to regulate greenhouse gas emissions. We evaluate the potential macroeconomic and climate impacts of carbon tax policy in Vietnam using a unique data set and simulation analysis with a multi-sector dynamic computable general equilibrium model. The model allows for firm heterogeneity: domestic firms and foreign-invested enterprises. The results show that with plausible tax rates, emissions can be reduced to levels 1.3-2.8 percent below the target value of emissions in 2030. The cost is a loss in GDP by 1.2-2.7 percent in 2030. The results also show that foreign-invested enterprises tend to increase emissions in the medium run even with a carbon tax while a carbon tax is more effective when applied to domestic firms. In addition, a substantial reduction in emissions from the energy sector and improvement in energy efficiency are keys to success in carbon abatement.

How an Audit-and-Feedback-Based Educational Program Contributed to a Reduction in Environmentally Harmful Waste Anesthetic Gases Among Anesthesiology Residents.

Background Waste anesthetic gases (WAGs) contribute to greenhouse gas emissions. US anesthesiology resident education on how to reduce WAG-associated emissions is lacking, so we developed an electronic audit-and-feedback-based program to teach residents to reduce fresh gas flow (FGF) and WAG-associated emissions. Objective To assess the program's effectiveness, we measured individual and combined mean FGF of residents during their first, second, and last weeks of the 4-week rotation; then, we calculated the extrapolated annual emissions based on the combined resident mean FGFs. Resident attitudes toward the program were surveyed. Methods During 4-week rotations at a teaching hospital, anesthesia records were scanned to extract resident-assigned cases, FGF, and volatile anesthetic choice during the 2020-2021 academic year. Forty residents across 3 training years received weekly FGF data and extrapolated WAG-associated emissions data via email. Their own FGF data was compared to the low-flow standard FGF of ≤1 liter per minute (LPM) and to the FGF data of their peer residents on rotation with them. An online survey was sent to residents at the end of the project period. Results Between their first and last weeks on rotation, residents decreased their mean FGF by 22% (1.83 vs 1.42 LPM; STD 0.58 vs 0.44; 95% CI 1.67-2.02 vs 1.29-1.56; P<.0001). Ten of 18 (56%) residents who responded to the survey reported their individual case-based results were most motivating toward practice change. Conclusions An audit-and-feedback-based model for anesthesiology resident education, designed to promote climate-conscious practices with administration of volatile anesthetics, was effective.

Climate impacts of landfill gas emissions: Analysis for 20-year and 100-year time horizons.

Climate impacts of landfill gas emissions were investigated for 20- and 100-year time horizons to identify the effects of atmospheric lifetimes of short- and long-lived drivers. Direct and indirect climate impacts were determined for methane and 79 trace species. The impacts were quantified using global warming potential, GWP (direct and indirect); atmospheric degradation (direct); tropospheric ozone forming potential (indirect); secondary aerosol forming potential (indirect) and stratospheric ozone depleting potential (indirect). Effects of cover characteristics, landfill operational conditions, and season on emissions were assessed. Analysis was conducted at five operating municipal solid waste landfills in California, which collectively contained 13% of the waste in place in the state. Climate impacts were determined to be primarily due to direct emissions (99.5 to 115%) with indirect emissions contributing -15 to 0.5%. Methane emissions were 35 to 99% of the total emissions and the remainder mainly greenhouse gases (hydro)chlorofluorocarbons (up to 42% of total emissions) and nitrous oxide. Cover types affected emissions, where the highest emissions were generally from intermediate covers with the largest relative landfill surface areas. Landfill-specific direct emissions varied between 683 and 103,411 and between 381 and 37,925 Mg CO2-eq./yr for 20- and 100-yr time horizons, respectively. Total emissions (direct + indirect) were 680 to 103,600 (20-yr) and were 374 to 38,108 (100-yr) Mg CO2-eq./yr. Analysis time horizon significantly affected emissions. The 20-yr direct and total emissions were consistently higher than the 100-yr emissions by up to 2.5 times. Detailed analysis of time-dependent climate effects can inform strategies to mitigate climate change impacts of landfill gas emissions.

Willingness to adopt green house gas mitigation measures: Agricultural land managers in the United Kingdom.

Rapid uptake of greenhouse gas (GHG) mitigation measures is central to reducing agricultural and land use emissions and meeting the UK Net Zero policy. The socioeconomic challenges and barriers to uptake are poorly understood, with yet unclear structural pathways to the uptake of GHG mitigation measures. Using an online survey of 201 agricultural land managers across the UK, and applying multiple linear regression and stepwise regression analysis, this research established farm and farmers' factors influencing perceptions and willingness to adopt GHG mitigation measures. The results consistently show that farm sector, farmers' business perception, and labour availability influence willingness to adopt GHG mitigation measures. Based on the farmers' qualitative feedback, other barriers to adoption include costs and concerns for profitability, lack of flexibility in land tenancy contracts, poor awareness and knowledge of the application of some GHG mitigation measures, perception about market demand e.g bioenergy crops, and scepticism about the future impacts of adopting varying GHG mitigation measures. In the midst of the ongoing net zero transition, this study identifies existing barriers to the uptake of GHG mitigation measures, and specifically, a substantial gap between farmers and the science of GHG mitigation measures and the need to incentivise a farm and farming community-led policy interventions to promote adoption of GHG mitigation measures.

Climate impacts of alternative beef production systems depend on the functional unit used: Weight or monetary value.

Beef production has been identified as a significant source of anthropogenic greenhouse gas (GHG) emissions in the agricultural sector. United States and Canada account for about a quarter of the world's beef supply. To compare the GHG emission contributions of alternative beef production systems, we conducted a meta-analysis of 32 studies that were conducted between 2001 and 2023. Results indicated that GHG emissions from beef production in North America varied almost fourfold from 10.2 to 37.6 with an average of 21.4 kg CO2e/kg carcass weight (CW). Studies that considered soil C sequestration (C-seq) reported the highest mitigation potential in GHG emissions (80%), followed by growth enhancement technology (16%), diet modification (6%), and grazing management improvement (7%). Our study highlights the implications of using carbon intensity per economic activity (i.e., GHG emissions per monetary unit), compared to the more common metric of intensity on per weight of product basis (GHG emissions per kg CW) for comparisons across differentiated beef cattle products. While a positive association was found between the proportion of lifespan on grassland and the conventional weight-based indicator, grass-finished beef was found to have lower carbon intensity per economic activity than feedlot-finished beef. Our study emphasizes the need to incorporate land use and management effects and soil C-seq as fundamental aspects of beef GHG emissions and mitigation assessments.

National Greenhouse Gas Emission Reduction Potential from Adopting Anaerobic Digestion on Large-Scale Dairy Farms in the United States.

Waste-to-energy systems can provide a functional demonstration of the economic and environmental benefits of circularity, innovation, and reimagining existing systems. This study offers a robust quantification of the greenhouse gas (GHG) emission reduction potential of the adoption of anaerobic digestion (AD) technology on applicable large-scale dairy farms in the contiguous United States. GHG reduction estimates were developed through a robust life cycle modeling framework paired with sensitivity and uncertainty analyses. Twenty dairy configurations were modeled to capture important differences in housing and manure management practices, applicable AD technologies, regional climates, storage cleanout schedules, and methods of land application. Monte Carlo results for the 90% confidence interval illustrate the potential for AD adoption to reduce GHG emissions from the large-scale dairy industry by 2.45-3.52 MMT of CO2-eq per year considering biogas use only in renewable natural gas programs and as much as 4.53-6.46 MMT of CO2-eq per year with combined heat and power as an additional biogas use case. At the farm level, AD technology may reduce GHG emissions from manure management systems by 58.1-79.8% depending on the region. Discussion focuses on regional differences in GHG emissions from manure management strategies and the challenges and opportunities surrounding AD adoption.

The challenge of estimating global termite methane emissions.

Methane is a powerful greenhouse gas, more potent than carbon dioxide, and emitted from a variety of natural sources including wetlands, permafrost, mammalian guts and termites. As increases in global temperatures continue to break records, quantifying the magnitudes of key methane sources has never been more pertinent. Over the last 40 years, the contribution of termites to the global methane budget has been subject to much debate. The most recent estimates of termite emissions range between 9 and 15 Tg CH4 year-1, approximately 4% of emissions from natural sources (excluding wetlands). However, we argue that the current approach for estimating termite contributions to the global methane budget is flawed. Key parameters, namely termite methane emissions from soil, deadwood, living tree stems, epigeal mounds and arboreal nests, are largely ignored in global estimates. This omission occurs because data are lacking and research objectives, crucially, neglect variation in termite ecology. Furthermore, inconsistencies in data collection methods prohibit the pooling of data required to compute global estimates. Here, we summarise the advances made over the last 40 years and illustrate how different aspects of termite ecology can influence the termite contribution to global methane emissions. Additionally, we highlight technological advances that may help researchers investigate termite methane emissions on a larger scale. Finally, we consider dynamic feedback mechanisms of climate warming and land-use change on termite methane emissions. We conclude that ultimately the global contribution of termites to atmospheric methane remains unknown and thus present an alternative framework for estimating their emissions. To significantly improve estimates, we outline outstanding questions to guide future research efforts.

Regulating greenhouse gas dynamics in tidal wetlands: Impacts of salinity gradients and water pollution.

Tidal wetlands play a critical role in emitting greenhouse gases (GHGs) into the atmosphere; our understanding of the intricate interplay between natural processes and human activities shaping their biogeochemistry and GHG emissions remains lacking. In this study, we delve into the spatiotemporal dynamics and key drivers of the GHG emissions from five tidal wetlands in the Scheldt Estuary by focusing on the interactive impacts of salinity and water pollution, two factors exhibiting contrasting gradients in this estuarine system: pollution escalates as salinity declines. Our findings reveal a marked escalation in GHG emissions when moving upstream, primarily attributed to increased concentrations of organic matter and nutrients, coupled with reduced levels of dissolved oxygen and pH. These low water quality conditions not only promote methanogenesis and denitrification to produce CH4 and N2O, respectively, but also shift the carbonate equilibria towards releasing more CO2. As a result, the most upstream freshwater wetland was the largest GHG emitter with a global warming potential around 35 to 70 times higher than the other wetlands. When moving seaward along a gradient of decreasing urbanization and increasing salinity, wetlands become less polluted and are characterized by lower concentrations of NO3-, TN and TOC, which induces stronger negative impact of elevated salinity on the GHG emissions from the saline wetlands. Consequently, these meso-to polyhaline wetlands released considerably smaller amounts of GHGs. These findings emphasize the importance of integrating management strategies, such as wetland restoration and pollution prevention, that address both natural salinity gradients and human-induced water pollution to effectively mitigate GHG emissions from tidal wetlands.

Techno-economic evaluation of GHG emissions mitigation of biomethane upgrading technologies.

The current trend in the European biogas industry is to shift away from electricity production towards the production of biomethane for the need to replace natural gas. The upgrading of biogas to biomethane is normally performed by separating the biogas in a stream containing natural gas grid quality methane and a stream containing mostly CO2. The CO2 stream is normally released into the atmosphere; however, part of the methane may still remain in it, and, if not oxidized, even a small fraction of methane released may jeopardise all the GHG emissions savings from producing the biomethane, being methane a powerful climate forcer. Scope of this work is to assess the opportunity cost of installing an Off Gas Combustion (OGC) device in biomethane upgrading plants. The currently available technologies for biogas upgrading to biomethane and the most common technology of OGC (the Regenerative Thermal Oxidisers, RTO) are described according to their performances and cost. Then the cost per tonne of CO2eq avoided associated to the adoption of RTO systems in relation to the upgrading performance is calculated to identify a potential threshold for an effective and efficient application of the RTO systems. It is found that, in case of upgrading technologies which can capture almost all biomethane in the upgrading off-gas (i.e. 99.9%), currently the adoption of an RTO to oxidise the methane left in the off-gas would add costs and need additional fuel to be operated, but would generate limited GHG emission savings, therefore the cost per tonne of CO2eq emissions avoided would result not competitive with other GHG emissions mitigation investments. While the installation of RTOs on upgrading systems with a methane slip of 0.3%, or higher, normally results cost competitive in reducing GHG emissions. The installation of an RTO on systems with a methane slip of 0.2% results in a cost per tonne of CO2eq emissions avoided of 50-100 euro, which is comparable to the current cost of CO2 emissions allowances in the EU ETS carbon market, representing therefore a reasonable choice for a threshold on methane slip regulation for biogas upgrading systems.

Reveling the micromolecular biological mechanism of acetate, thiosulfate and Fe0 in ecological floating beds for treating low C/N wastewater: Insight into nitrogen removals and greenhouse gases reductions.

Selecting an appropriate electron donor to enhance nitrogen removal for treating low C/N wastewater in ecological floating beds (EFBs) is controversy. In this study, a systematic and comprehensive evaluation of sodium acetate (EFB-C), sodium thiosulfate (EFB-S) and iron scraps (EFB-Fe) was performed in a 2-year experiment on long-term viability including nitrogen removal and greenhouse gas emissions associated with key molecular biological mechanisms. The results showed that EFB-C (43-85 %) and EFB-S (40-88 %) exhibited superior total nitrogen (TN) removal. Temperature and hydraulic retention time (HRT) have significant impacts on TN removal of EFB-Fe, however, it could reach 86 % under high temperature (30-35 °C) and a long HRT (3 days), and it has lowest N2O (0-6.2 mg m-2 d-1) and CH4 (0-5.3 mg m-2 d-1) fluxes. Microbial network analysis revealed that the microbes changed from competing to cooperating after adding electron donors. A higher abundance of anammox genera was enriched in EFB-Fe. The Mantel's test and structural equation model provided proof of the differences, which showed that acetate and thiosulfate were similar, whereas Fe0 was different in the nitrogen removal mechanism. Molecular biology analyses further verified that heterotrophic, autotrophic, and mixotrophic coupled with anammox were the main TN removal pathways for EFB-C, EFB-S, and EFB-Fe, respectively. These findings provide a better understanding of the biological mechanisms for selecting appropriate electron donors for treating low C/N wastewater.