CH4 Reduction Research Articles

Water-based Silicalite-1 porous liquid facilitates adsorption and absorption for CH4 capture

As the key to open the Pandora’s box of gas efficient capture, water-based porous liquids have doubled the popular attention. Nevertheless, the synthesis of water-based porous liquids is a significant challenge due to the inherent limitation in the wettability of nanoporous hosts. In this work, Silicalite-1 was prepared by hydrothermal synthesis, based on which a water-based porous liquid of S-1-PL was successfully prepared, and CH4 capture in the porous liquid via adsorption-absorption synergistic approach was evaluated. It was demonstrated that S-1-PL exhibited excellent stability and flowability, with a pore opening ratio up to 90 %. CH4 capture capacity in S-1-PL with the solid content of 15 wt% was 0.57 mol/L, which was 2.6 times that in pure water system, demonstrating excellent CH4 physisorption performance. When the adsorption-absorption synergistic approach was employed, CH4 capture capacity increases to 1.88 mol/L with an increase by 229.8 %. In addition, a hydrate nano-promoter of −SO3-@PSNS was prepared to enhance hydration efficiency, which resulted in a notable enhancement in the hydration conversion rate, and it increases from 12.54 % to 61.99 % in the system of S-1-PL15wt%, giving rise to a significant increase in CH4 capture to 6.22 mol/L, which is 12.67 times that in the system of −SO3-@PSNS solution. These findings provide clear evidence for the first time on the exceptional adaptability of water-based porous liquid for the capture of CH4 by adsorption-absorption synergistic approach, offering a new strategy for the emission reduction of CH4.

Sources and Variability of Greenhouse Gases over Greece

This study provides an overview of the atmospheric drivers of climate change over Greece (Eastern Mediterranean), focusing on greenhouse gases (GHG: carbon dioxide, CO2; methane, CH4; etc.). CO2 in Greece is mostly produced by energy production, followed by transport, construction, and industry. Waste management is the largest anthropogenic source of methane, accounting for 47% of total CH4 emissions, surpassing emissions from the agricultural sector in 2017, while the energy sector accounts for the remaining 10.5%. In situ simultaneous observations of GHG concentrations in Greece conducted at three sites with different topologies (urban background; Athens, regional background; Finokalia and free troposphere; and Helmos) during the last 5 years (2019–2023) showed increasing trends of the order of 2.2 ppm·yr−1 and ~15 ppb·yr−1 for CO2 and CH4, respectively, in line with the global trends. These increasing trends were found from both ground-based and satellite-based remote-sensing observations. Finally, during the lockdown period due to the COVID-19 global pandemic, a 58% reduction in CO2 levels was observed in the urban background site of Athens after subtracting the regional background levels from Finokalia, while the respective reduction in CH4 was of only the order of 15%, highlighting differences in emission sources.

Boosted Solar Thermochemical Low-Temperature CO2 Splitting On Pt/CeO2 by Interface Catalysis.

Solar thermochemical CO2 splitting using metal oxides is considered as a promising approach to produce solar fuels since it is capable to tap abundant sunlight directly and store solar energy in the renewable fuel. It remains a grand challenge to achieve highly efficient CO2 splitting at low temperature (<800 °C) due to insufficient activation of metal oxides for CO2. Herein, the introduction of a small amount of Pt was found to be able to greatly increase the performance of CO2 splitting with the highest peak CO production rate of about 65 mL min-1 g-1, CO productivity of about 53 mL g-1, nearly 100 % CO2 conversion and long-term stability for 0.5Pt/CeO2, which exceeded most of the state-of-the-art transition metals-based oxides even at lower temperature (700 °C). This could be attributed to the addition of Pt leading to the formation of an interface (Pt0-Ov-Ce3+) after CH4 reduction, which improved CO2 activation and dissociation due to beneficial breakage of C=O bond by the cooperation of Pt0 and oxygen vacancies in the interface.

Impact of methane and other precursor emission reductions on surface ozone in Europe: scenario analysis using the European Monitoring and Evaluation Programme (EMEP) Meteorological Synthesizing Centre – West (MSC-W) model

Abstract. The impacts of future methane (CH4) and other precursor emission changes are investigated for surface ozone (O3) in the United Nations Economic Commission for Europe (UNECE) region excluding North America and Israel (the EMEP region, for European Monitoring and Evaluation Programme) for the year 2050. The analysis includes a current legislation (CLE) and maximum feasible technical reduction (MFR) scenario, as well as a scenario that combines MFRs with an additional dietary shift that also meets the Paris Agreement objectives with respect to greenhouse gas emissions (LOW). For each scenario, background CH4 concentrations are calculated using a probabilistic Earth system model emulator and combined with other precursor emissions in a three-dimensional Eulerian chemistry-transport model. While focus is placed on peak season maximum daily 8 h average (MDA8) O3 concentrations, a range of other indicators for health and vegetation impacts are also discussed. Our analysis shows that roughly one-third of the total peak season MDA8 reduction achieved between the 2050 CLE and MFR scenarios is attributable to CH4 reductions, resulting predominantly from CH4 emission reductions outside of the EMEP region. The impact of other precursor emission reductions is split nearly evenly between the reductions inside and outside of the EMEP region. However, the relative importance of CH4 and other precursor emission reductions is shown to depend on the choice of O3 indicator, though indicators sensitive to peak O3 show generally consistent results. The analysis also highlights the synergistic impacts of CH4 mitigation as reducing solely CH4 achieves, beyond air quality improvement, nearly two-thirds of the total global warming reduction calculated for the LOW scenario compared to the CLE case.

CH4 and CO2 Reductions from Methanol Production Using Municipal Solid Waste Gasification with Hydrogen Enhancement

This study evaluates the greenhouse gas (GHG) impacts of converting municipal solid waste (MSW) into methanol, focusing on both landfill methane (CH4) emission avoidance and the provision of cleaner liquid fuels with lower carbon intensity. We conduct a life cycle assessment (LCA) to assess potential GHG reductions from MSW gasification to methanol, enhanced with hydrogen produced via natural gas pyrolysis or water electrolysis. Hydrogen enhancement effectively doubles the methanol yield from a given amount of MSW. Special attention is given to hydrogen production through natural gas pyrolysis due to its potential for lower-cost hydrogen and reduced reliance on renewable electricity compared to electrolytic hydrogen. Our analysis uses a case study of methanol production from an oxygen-fired entrained flow gasifier fed with refuse-derived fuel (RDF) simulated in Aspen HYSYS. The LCA incorporates the significant impact of landfill methane avoidance, particularly when considering the 20-year global warming potential (GWP). Based on the LCA, the process has illustrative net GHG emissions of 183 and 709 kgCO2e/t MeOH using renewable electricity for electrolytic hydrogen and pyrolytic hydrogen, respectively, for the 100-year GWP. The net GHG emissions using 20-year GWP are −1222 and −434 kgCO2e/t MeOH, respectively. Additionally, we analyze the sensitivity of net GHG emissions to varying levels of fugitive methane emissions.

Response of denitrifying anaerobic methane oxidation processes in freshwater and marine sediments to polyvinyl chloride microplastics.

Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) plays a crucial role in mitigating methane (CH4) in natural environments. The increasing presence of microplastics (MPs) in these environments due to human activities is a growing concern. However, the impact of MPs on n-DAMO microorganisms and their role in greenhouse gas regulation, particularly CH4 reduction, remains unclear. This study investigates the effects of polyvinyl chloride (PVC) MPs on n-DAMO activity and the associated microbial communities in freshwater and marine sediments at varying concentrations of (R0/M0-no addition, R1/M1-0.5 %, R2/M2-2%). The results showed that the presence of MPs significantly increased the n-DAMO rate (2.89-3.58 nmol 13CO2 g-1 d-1) compared to the control groups (R0: 1.29 nmol 13CO2 g-1 d-1, M0: 0.11 nmol 13CO2 g-1 d-1), with marine sediments showing a more pronounced response. Additionally, the proportional contribution of nitrate-DAMO processes increased following MP exposure. The presence of PVC MPs also altered the microbial diversity of n-DAMO. Upon the addition of MPs, the microbial community composition of n-DAMO in marine sediments changed more significantly. This study provides the first evidence of a positive impact of PVC MPs on n-DAMO processes, suggesting that the presence of PVC MPs in sediments could potentially contribute to the reduction of CH4 emissions.

New insights into the enteric methane production based on the archaeal genome map of ruminant gastrointestinal tract

IntroductionAs one of the important components of ruminant gastrointestinal tract (GIT) microbiome, archaea are involved in many biological processes, especially methanogenesis. However, the diversity and individual metabolic characteristics of archaea in this habitat remain largely understudied, partly due to the lack of a unified reference genome catalog. ObjectivesThis study aimed to construct a unified genome map for taxonomic and functional exploration of ruminant GIT archaea in the future. MethodsWe collected archaeal genomes from public sources and new data of this study. We performed phylogenetic analysis, functional genomics analyses, prophages identification based on the genomes. Using collected genomes as a reference, we conducted metagenomic and metatranscriptomic analyses on rumen fluid samples from 18 dairy cows with different methane (CH4) production. ResultsWe constructed the ruminant GIT archaeal genomes (RGAG) by compiling 405 strain-level (160 species) non-redundant archaeal genomes from more than 10 ruminant species. The functional heterogeneity and methanogenic structure within RGAG was investigated. RGAG possessed 1,124 (99.5 %) unknown microbial biosynthetic gene clusters. A survey of RGAG-borne prophages identified 63 prophages with 122 host-beneficial genes and 18 auxiliary metabolic genes (AMGs). The pipeline for both metagenomics and metatranscriptomics generated in the study revealed the roles of archaeal genomes under-assessed in general analyses of muti-omics. The highly expressed genus Methanosphaera was negatively correlated with CH4 production. ConclusionA unified genome map of ruminant GIT archaea is constructed in the study. Functional genomics indicates that the multifaceted functions of RGAG remains undiscovered. Multi-omics analyses reveals the advantages of metatranscriptomics over metagenomics in studying rumen archaeal communities. Differences in rumen archaeal community structure among cattle with different CH4 production may reflect the balance between rumen hydrogen production and methanogenesis. Our work provides new understanding of archaeal functions in the ruminant GIT and potential targets for future CH4 reduction.

Experimental Design, Statistical Analysis, and Modeling of the Reduction in Methane Emissions from Dam Lake Treatment Using Agro-Industrial Biochar: A New Methane Capture Index

This study aimed to reduce the methane (CH4) emissions originating from dam lake treatment using malt dust-derived biochar, which is an agro-industrial byproduct of the brewery industry. Optimum operating and water quality parameters for CH4 reduction were determined using statistical analyses based on the Box–Behnken design method. Also, a Monte Carlo simulation was performed to determine the correlation between CH4 emissions and operating parameters. According to the simulation, dissolved oxygen (DO) and the oxidation–reduction potential (ORP) had the highest correlation with CH4 emissions, with values of 92.03% and 94.57%, respectively. According to the Box–Behnken design methodology, the optimum operating parameters were 4 mg/L of dissolved oxygen, −359 mV of ORP, and 7.5 pH for the minimum CH4 emissions. There was a reported reduction of up to 19.4% in CH4 emissions for the dam lake treatment using malt dust-derived biochar. Finally, a new methane capture index, based on the biochar application (MCI), was developed and validated. The largest methane capture capacity was related to the malt dust-derived biochar produced at the lowest temperature (M1).

Emerging research on characterizing the potential of cable bacteria for CH4 mitigation

Methane (CH4) contributes an essential portion for global warming as a pivotal greenhouse gas. Microorganisms are identified as an effective way to mediate and control CH4 emission. Cable bacteria is a promising microorganism to mitigate CH4, however, the studies of distribution, abundance and function for CH4 reduction of cable bacteria in inland water still remain unclear. In this paper, we propose the probable CH4 mitigation metabolism within cable bacteria in anoxic condition, and present the future research directions about the application potential of cable bacteria in CH4 reduction. The viewpoint will help to understand the significant role of cable bacteria in CH4 mitigation and provide a potential way to control CH4 emissions in inland freshwater ecosystem.

Economic and environmental benefits of optimized waste transportation routes in Khulna

Urban transportation is a big source of pollution and greenhouse gas emissions. Khulna City handles the waste of 1.23 million people daily, using Heavy Duty Diesel Vehicles (HDDV) that release major environmental pollutants. The current waste transportation routes lack proper planning, leading to extra fuel consumption and pollutant emissions. This study aims to reduce fuel consumption and socio-environmental costs by improving waste transportation routes. Present collection routes, collecting points, and the speed of 30 waste collector vehicles were tracked using GPS devices for ten months between July 2023 and April 2024. The network dataset was modified according to four types of waste collector vehicles. ArcGIS Pro was used to find the optimal paths and their lengths. Fuel usage and prices were estimated using simple fuel consumption rate calculations. The lengths of current and optimal routes were used in COPERT to measure pollutant emissions. The results show that improved routes lower fuel consumption costs by approximately USD 55.39 per day and CO2 emissions by about 38.242 tonnes per year. Reductions in CO, CH4, NMVOC, NO2, PM10, and PM2.5 were roughly 9.3%, 9.53%, 9.21%, 9.29%, 9.35%, and 9.3%, respectively. This study demonstrates a comprehensive approach for improving solid waste management covering both financial efficiency and environmental effects.

94 Associative effects of two potent anti-methanogenic Moringa oleifera accessions mixed at various proportions on in vitro rumen fermentation and methane inhibition

Abstract Moringa is an important anti-methanogenic plant with a potential to develop as multipurpose feed additives. Previous studies identified two potent accessions (accession 07633 designated as A3 and accession collected from Pretoria designated as A11) with high methane (CH4) inhibition characteristics. Two metabolite ion features (MIFs) 4.44_609.1462 and MIF 4.53_433.1112 were identified as bioactive MIFs associated with greater methane inhibition in Moringa accession A3 and A11, respectively. Two separate studies were conducted with an aim to name the MIF associated with methane inhibition and evaluate the benefit of mixing plant extract from A3 and A11 in different proportions to exploit their additive or synergistic effect in inhibiting CH4 emission. In study 1, software and online tools such as MS-DIAl, MS-FINDER, and the mass bank database were used to identify the MIF 4.44_609.1462 and MIF 4.53_433.1112, and the two MIFs were tentatively named as Hesperidin and Isovitexin, respectively (Figure 1). In study 2, the Moringa plant extracts from A3 and A11 were mixed in the following proportion A3100:A110, A380:A1120, A360:A1140, A350:A1150, A340:A1160, A320:A1180, and A30:A11100 proportions (A3:A11), and applied at a rate 50 mg/kg DM of Eragrostis curvula hay incubated in an Incoshake incubator to determine their effect on in vitro gas production and CH4, and in vitro organic matter digestibility (IVOMD) of the hay. In each incubation run, the sole or a mixture of the Moringa plant extract treatments were added to the test feed and incubated in 125 mL serum bottles with four replications per treatment, and the incubation was repeated for three runs. A Chi–square (☐2) test were used to determine the presence of an associative effect for mixtures combined at different proportion. Generally, the mixture resulted in less (P &amp;lt; 0.05) CH4 volume, slightly improved or no effect on IVOMD, propionate concentration decreased acetate while increasing propionate concentration, with higher CH4 inhibition, and % CH4 inhibition was significantly greater when the two accessions were mixed in 50% proportion (Figure 2). Specifically, associative effects were recorded when the two accessions are mixed in 50% proportion in terms of greater CH4 inhibition, propionic acid concentration and total volatile fatty acid production (TVFA), as well as reduction in CH4 per unit TVFA and C2:C3 ratio (Table 1). Therefore a 50% binary cocktail of M. oleifera accession A3 and A11 (A350:A1150) plant extracts can be used as feed additive for CH4 inhibition without affecting the feed fermentation adversely when compared with the sole accession leaf extracts or other proportions of binary cocktails. Detailed mechanisms of action, however, need to be confirmed.

Controlling Methane Ebullition Flux in Cascade Reservoirs of the Upper Yellow River by the Ratio of mcrA to pmoA Genes

Reservoirs are an important source of methane (CH4) emissions, but the relative contribution of CH4 ebullition and diffusion fluxes to total fluxes has received little attention in the past. In this study, we systematically monitored the CH4 fluxes of nine cascade reservoirs (Dahejia, Jishixia, Huangfeng, Suzhi, Kangyang, Zhiganglaka, Lijiaxia, Nina, and Longyangxia) in the upper reaches of the Yellow River in the dry (May 2023) and wet seasons (August 2023) using the static chamber gas chromatography and headspace equilibrium methods. We also simultaneously measured environmental physicochemical properties as well as the abundance of methanogens and methanotrophs in sediments. The results showed the following: (1) All reservoirs were sources of CH4 emissions, with an average diffusion flux of 0.08 ± 0.05 mg m−2 h−1 and ebullition flux of 0.38 ± 0.41 mg m−2 h−1. Ebullition flux accounted for 78.01 ± 7.85% of total flux. (2) Spatially, both CH4 diffusion and ebullition fluxes increased from upstream to downstream. Temporally, CH4 diffusion flux in the wet season (0.09 ± 0.06 mg m−2 h−1) was slightly higher than that in the dry season (0.08 ± 0.04 mg m−2 h−1), but CH4 ebullition flux in the dry season (0.38 ± 0.48 mg m−2 h−1) was higher than that in the wet season (0.32 ± 0.2 mg m−2 h−1). (3) qPCR showed that methanogens (mcrA gene) were more abundant in the wet season (5.43 ± 3.94 × 105 copies g−1) than that in the dry season (3.74 ± 1.34 × 105 copies g−1). Methanotrophs (pmoA gene) also showed a similar trend with more abundance found in the wet season (7 ± 2.61 × 105 copies g−1) than in the dry season (1.47 ± 0.92 × 105 copies g−1. (4) Structural equation modeling revealed that the ratio of mcrA/pmoA genes, water N/P, and reservoir age were key factors affecting CH4 ebullition flux. Variation partitioning further indicated that the ratio of mcrA/pmoA genes was the main factor causing the spatial variation in CH4 ebullition flux, explaining 35.69% of its variation. This study not only reveals the characteristics and influencing factors of CH4 emissions from cascade reservoirs on the Qinghai Plateau but also provides a scientific basis for calculating fluxes and developing global CH4 reduction strategies for reservoirs.

Energy utilization in lactating Jersey cows consuming a mixture of DDGS and straw replacing alfalfa hay

Some forages require significant amounts of water to grow, causing the dairy industry to be dependent on a limited resource. Feeding crop residues and feed coproducts in dairy rations may represent opportunities when alfalfa is not readily available, and to reduce the industry's use of water. A study using indirect calorimetry and 12 multiparous lactating Jersey cows (BW = 447.5 ± 43.7 kg; DIM = 71 ± 11 d, mean ± SD) was conducted to determine the effect of feeding dried distillers grains and solubles (DDGS) and straw in replacement of alfalfa hay on milk production and energy utilization. A triplicated 4 × 4 Latin square design was used to evaluate the replacement of alfalfa hay with a coproduct mixture (COP) of wheat straw and DDGS. Animals were blocked by milk yield and randomly assigned to 1 of 4 experimental treatments including (proportions on a DM basis): a control diet (CON) containing 18.2% of alfalfa hay, a low-coproduct diet (LCOP) that contained 8.1% of COP, a medium-coproduct diet (MCOP) that contained 16.3% of COP, and a high-coproduct diet (HCOP) that contained 24.3% of COP. No differences were observed for daily dry matter intake or milk yield (mean ± SEM) 19.5 kg ± 0.60, 29.6 kg ± 0.91, respectively. A quadratic tendency was observed where increasing inclusion of COP up to 16.3% maintained ECM and milk fat yield but decreased when animals were fed 24.3% COP. Total methane production decreased linearly from 429.4 to 345.0 ± 22.8 L/d from CON to HCOP diets, respectively. The digestibility of CP increased linearly from 64.0 to 70.4 ± 0.95% and N balance increased linearly from 43.3 to 90.7 ± 15.0 g/d in animals consuming CON to HCOP diets. Total time spent ruminating was lowest in animals consuming the HCOP diet. A linear increasing tendency in digestible and metabolizable energy of 2.92 to 3.02 ± 0.041 Mcal/kg and 2.58 to 2.70 ± 0.047 Mcal/kg was observed in animals consuming CON to HCOP. The proportion ME from DE (ME/DE) tended to linearly increase from 88.3 to 89.4 ± 0.454 when COP was added to the diet. Results of this study indicate that alfalfa hay with a mixture of straw and DDGS can maintain milk production and DMI, but the partial or full replacement of alfalfa with the COP mixture may result in differences in energy utilization in part driven by effects on CH4 reduction.

Dietary supplementation with calcium peroxide improves methane mitigation potential of finishing beef cattle

Calcium peroxide (CaO2) offers potential as an anti-methanogenic dietary feed material. The compound has been previously assessed in vitro, with methane (CH4) reductions of > 50% observed. The objective of this study was to assess dietary supplementation of CaO2 at different inclusion levels and physical formats in a finishing beef system on the effects of animal performance, gaseous emissions, rumen fermentation parameters and digestibility. Seventy-two dairy-beef bulls (465 kg; 16 months of age) were randomly allocated to one of four treatments supplemented with CaO2; in a coarse ration (1) CON (0% CaO2), (2) LO (1.35% CaO2), (3) HI (2.25% CaO2), and in a pellet (4) HP (2.25% CaO2) (n = 18). Animals received their respective treatments for a 77 d finishing period, during which DM intake (American Calan Inc., Northwood, NH), average daily gain (ADG), feed efficiency and enteric emissions (GreenFeed emissions monitoring system; C-Lock Inc., Rapid City, SD) were measured. The finishing diet was isonitrogenous and isoenergetic across the four treatment groups, composed of 60:40 grass silage:concentrate. Silage was offered each morning (0900 h), and concentrates were offered twice daily (0800 and 1500 h). Supplementation of CaO2 had no effect on final weight (P = 0.09), ADG (P = 0.22) or feed efficiency (P = 0.13). Regarding DM intake, the HI treatment group consumed in the order of 1 kg less than CON (P < 0.01), while HP did not affect DM intake compared to CON (P = 0.79). Across treatments, DM intake ranged from 8.43 to 9.57 kg/d, equating to 1.6–1.8% of BW. Daily CH4 values for the control were 240 g/d, while CaO2 supplemented diets ranged from 202 to 170 g/d, resulting in daily CH4 reductions of 16, 29 and 27% for LO, HI and HP, respectively, compared to CON (P < 0.0001). Additionally, hydrogen was reduced in CaO2 supplemented animals by 32–36% relative to CON (P < 0.0001), with a simultaneous reduction in volatile fatty acid production (P < 0.01) and an increase in propionate concentration (P < 0.0001). Across all universally accepted CH4 metrics (yield, intensity, production), the dietary inclusion of CaO2 whether at a low or high rate, or indeed, through a coarse ration or pelleted format reduced CH4 in the order of 16–32%. This study also concluded that CaO2 can successfully endure the pelleting process, therefore, improving ease of delivery if implemented at farm level.

Effects of a Proprietary Kelp Blend Product on Enteric Methane Production and Tissue Residues in Cattle.

Three experiments were performed investigating bovine enteric methane (CH4) production inhibition using a proprietary kelp blend product (PKBP) containing a halogenated methane analog (i.e., bromoform). Calves were fed a corn-silage basal diet top-dressed with the assigned treatment, with rations provided at 1.5 × NEm in Experiments 1 and 2 (n = 12 and 6 steers, respectively) and ad libitum in Experiment 3 (n = 9 steers). In Experiment 1, we evaluated bromoform's potency in decreasing CH4. Dry matter intake (DMI) was not affected by treatment (p ≥ 0.11; 0 vs. 52.5 ± 10.5 ppm bromoform), whereas bromoform supplementation decreased CH4 (p < 0.01). In Experiments 2 and 3, treatments were 0, 9.5 ± 1.5, or 20 ± 3 ppm bromoform. In Experiment 2, we examined CH4 recovery following bromoform removal from the ration. Bromoform treatments were fed on d1, but not the subsequent 8 d, to investigate residual effects. On d1, CH4 was below limits of detection for 20 ppm bromoform inclusion. Across days, a cubic response (p < 0.01) was observed with 20 ppm bromoform inclusion, but not with 0 and 9.5 ppm inclusion levels. Experiment 3 (30 d finishing trial) tested bromoform effects on feeder calves. DMI (p = 0.53), average daily gain (p = 0.55), and gain:feed (p = 0.82) were not influenced by bromoform inclusion. Bromoform residues were undetectable in liver, kidney, adipose, and muscle samples collected at harvest. These experiments demonstrated that cattle fed PKBP experience short-term reductions in CH4 without tissue accumulation of bromoform and without evidence of effects on animal growth or feed consumption.

Beyond the single-basket mindset: a multi-gas approach to better constrain overshoot in near term warming

Abstract The remaining carbon budget framework tracks progress towards the Paris Agreement’s goal to limit longer-term warming to well below 2 °C, but no analogous framework exists for constraining mid-century warming. Established single-basket methods of combining gases into CO2-equivalents using Global Warming Potentials (GWPs) lead to ambiguity over what combination of short- and long-lived emissions reductions are needed because they obscure the distinct warming impacts of each. We investigate to what extent a multi-basket approach that separates short-lived and long-lived pollutants can better estimate the likelihood for emission pathways to meet a near-term warming goal. We develop logistic regression models to categorize IPCC emission pathways (AR6) based on whether they exceed a mid-century temperature threshold. We focus on two baskets, using CO2 for long-lived and methane (CH4) for short-lived gases. For comparison, we consider several single-basket approaches (e.g. GWP100, GWP20, GWP*). We further apply our framework to a synthetic dataset covering a broader emissions space. Across both datasets, the two-basket outperforms all single-baskets. Using an illustrative near-term goal (1.7 °C), the two-basket approach reduces the magnitude of overshoot by a factor of 7 compared with the traditional single-basket. The two-basket’s advantage is smaller with the AR6 pathways, which we attribute to the high correlation between CO2 and CH4 emissions and confounding effects from other pollutants. Our results indicate that the two-basket approach better constrains overshoot magnitude, particularly if future emissions deviate from the AR6 assumption of correlated CO2 and CH4 reductions. Our approach allows the determination of a metric value and reduction target in the context of a chosen set of scenarios and temperature threshold; the outcome is a near-term methane-specific emissions budget that can be adopted by decisionmakers in a way that is analogous and complementary to the carbon budget. Future work could consider a third basket for very short-lived pollutants.

Improving contaminant removal and inhibiting CH4 and H2S emissions from septic tanks: Nitrified human urine as a source of electron acceptor

Septic tanks are widely adopted in decentralized household wastewater treatment systems serving billions of people globally. Due to the lack of effective electron acceptors, insufficient nutrient removal and the emission of harmful gases, e. g. H2S, CH4, etc., are the common drawbacks. In the present work, we attempted to supplement nitrite into septic tanks as an electron acceptor, via nitrifying human urine source-separated from blackwater, to overcome these drawbacks. Partial or complete nitritation of source-separated urine was achieved in a sequencing batch reactor. The addition of nitrified urine into septic tanks improved organic and nitrogen removals in blackwater up to 90 % and 70 %, respectively. The emission of harmful gases from the septic tanks was stably diminished, with more than 75 % of CH4, CO2 and H2S reductions. Nitrite addition significantly reduced the abundance of hydrogenotrophic methanogens in septic tanks. Though the activity of sulfate-reducing bacteria recovered after the initial inhibition upon nitrite addition, the bio-generated H2S was retained in water since the increased wastewater pH after nitrite addition promoted the disassociation of H2S in aqueous solution.

Retrieval of dominant methane (CH4) emission sources, the first high-resolution (1–2 m) dataset of storage tanks of China in 2000–2021

Abstract. Methane (CH4) is a significant greenhouse gas in exacerbating climate change. Approximately 25 % of CH4 is emitted from storage tanks. It is crucial to spatially explore the CH4 emission patterns from storage tanks for efficient strategy proposals to mitigate climate change. However, due to the lack of publicly accessible storage tank locations and distributions, it is difficult to ascertain the CH4 emission spatial pattern over a large-scale area. To address this problem, we generated a storage tank dataset (STD) by implementing a deep learning model with manual refinement based on 4403 high-spatial-resolution images (1–2 m) from the Gaofen-1, Gaofen-2, Gaofen-6, and Ziyuan-3 satellites over city regions in China with officially reported numerous storage tanks in 2021. STD is the first storage tank dataset for over 92 typical city regions in China. The dataset can be accessed at https://doi.org/10.5281/zenodo.10514151 (Chen et al., 2024). It provides a detailed georeferenced inventory of 14 461 storage tanks wherein each storage tank is validated and assigned the construction year (2000–2021) by visual interpretation of the collected high-spatial-resolution images, historical high-spatial-resolution images of Google Earth, and field survey. The inventory comprises storage tanks with various distribution patterns in different city regions. Spatial consistency analysis with the CH4 emission product shows good agreement with storage tank distributions. The intensive construction of storage tanks significantly induces CH4 emissions from 2005 to 2020, underscoring the need for more robust measures to curb CH4 release and aid in climate change mitigation efforts. Our proposed dataset, STD, will foster the accurate estimation of CH4 released from storage tanks for CH4 control and reduction and ensure more efficient treatment strategies are proposed to better understand the impact of storage tanks on the environment, ecology, and human settlements.

Direct reduction of calcium carbonate by coupling with methane dry reforming using NiO/S-1 as catalyst

Thermal decomposition of carbonate is an important process in the production of cement, refractory materials, and steel. Nevertheless, this process requires high temperature and is always accompanied with large amounts of CO2 emission. To reduce the decomposition temperature and simultaneously mitigate CO2 emissions, direct reduction of carbonate under a reducing atmosphere has been proposed as a novel strategy. This work mainly investigated the feasibility of direct reduction of CaCO3 by CH4 in the presence of a highly dispersed NiO/S-1 catalyst. It was found that the introduction of a CH4 atmosphere without a catalyst had little promotion effect on CaCO3 decomposition (as compared to air atmosphere), and no notable conversion of CO2 was observed. However, the presence of a highly dispersed NiO/S-1 catalyst significantly decreased the decomposition temperature of CaCO3 in a CH4 atmosphere, and most of the carbon species in CaCO3 can be converted to CO. To gain a comprehensive understanding of CaCO3 reduction in CH4, the effects of reaction temperature, CH4 concentration, and NiO loading in the NiO/S-1 catalyst were systematically explored. With the best-performing catalyst, i.e., 7NiO/S-1, complete CaCO3 decomposition and approximate 90 % CH4/CO2 conversion can be achieved under the condition of 750 °C and 25 vol% CH4. Characterization results indicated that the CaO particles obtained in the CH4 reducing atmosphere exhibited a more porous structure compared to that attained in air, due to the more intensive CaCO3 decomposition in CH4. Further data analysis revealed that reverse water-gas shift reaction also contributed to CO2 conversion during the reduction of CaCO3 in CH4. The findings obtained in this research can provide new perspectives for CO2 emission control and energy saving in traditional heavy-emission and high energy consumption industries.

Loss of microbial diversity increases methane emissions and arsenic release in paddy soils

Microorganisms are vital to the emission of greenhouse gases and transforming pollutants in paddy soils. However, the impact of microbial diversity loss on anaerobic methane (CH4) oxidation and arsenic (As) reduction under flooded conditions remains unclear. In this study, we inoculated microbial suspensions into natural As-contaminated paddy soils using a dilution approach (untreated, 10−2, 10−4, 10−6, 10−8 dilutions) to manipulate microbial diversity levels. The results revealed that the 10−4 and 10−6 dilutions resulted in the highest CH4 emissions (97.0 μmol and 102.3 μmol) compared to untreated groups (27.6 μmol). However, anaerobic CH4 oxidation was not observed in 10−4 dilution groups and higher dilutions, suggesting the loss of diversity inhibited the natural reduction of CH4. Moreover, the porewater As concentration in the dilution groups was 1.8–8.2 times greater than in the untreated groups. The loss of microbial diversity promoted the reductive dissolution of iron (Fe) minerals bearing As, leading to increased concentrations of Fe(II) and dissolved organic carbon (DOC), which further enhanced As release (Fe(II), R = 0.9, p < 0.001) (DOC, R = 0.8, p < 0.001) from soil to porewater. However, CH4-dependent As(V) reduction was almost entirely inhibited under diversity loss. The decline in microbial diversity increased the relative abundances of methanogens (e.g., Methanobacterium and Methanomassiliicoccus), Fe(III)/As(V)-reducing bacteria (e.g., Bacillus, Clostridium_sensu_stricto_10, and Geobacter), and the related functional genes (i.e., mcrA and Geo). These findings suggest that microbial diversity is critical for specialized soil processes, highlighting the detrimental effects of biodiversity loss on CH4 emissions and As release in As-contaminated paddies.