This week’s publications cover a wide range of matters related to direct air capture, biochar, enhanced alkalinity and carbon mineralization.
Fuel from Air: A Techno-economic Assessment of E-fuels for Low-Carbon Aviation in China
Aviation remains one of the most challenging sectors to achieve low carbon emissions due to its heavy reliance on fossil fuels and the lack of cost-competitive alternatives. This study evaluates the potential of Direct Air Capture (DAC)-based e-fuels to meet China’s aviation fuel demand by 2050. The research assesses e-fuel production costs and resource requirements under diverse scenarios, incorporating spatio-temporal variations in electricity, water, transportation, and policies. Results show that DAC capital costs and the energy market are the primary determinants. Liquid absorbent DAC (L-DAC), with lower capital costs but higher resource demands, is suitable for resource-abundant regions, while solid absorbent DAC (S-DAC), benefiting from higher learning rates and lower resource requirements, is optimal for water-scarce, high-demand regions like Beijing and Shanghai. By 2050, China could produce 102 Mt of e-fuels, meeting 84% of its demand, requiring 3457 TWh of renewable electricity and 597 billion liters of water, 78% of which would come from desalination. E-fuel costs range from $3176/ton (S-DAC) to $3208/ton (L-DAC), remaining 2.5–4 times higher than fossil jet fuels. Achieving cost parity requires low electricity prices (∼$5/GJ), high DAC learning rates ($80–50/ton), and strong policy incentives. This could reduce e-fuel costs to $900–1000/ton. The study also evaluates an alternative pathway involving Direct Air Capture with Carbon Storage paired with fossil fuel utilization. While this route offers cost and energy efficiency, it may raise long-term sustainability concerns. These findings underscore the potential of e-fuels for net-zero aviation targets, highlighting the urgency of supportive policies to scale their deployment effectively.
Tiwari, S. et al. (2025) Fuel from Air: A Techno-economic Assessment of E-fuels for Low-Carbon Aviation in China. 333 (119796) Energy Conversion and Management.
Read the full paper here: Fuel from Air: A Techno-economic Assessment of E-fuels for Low-Carbon Aviation in China I Energy Conversion and Management.
Evaluating the Two-Pool Decay Model for Biochar Carbon Permanence
Accurate estimation of biochar carbon permanence is essential for assessing its effectiveness as a carbon dioxide removal (CDR) strategy. The widely adopted framework, based on the two-pool carbon exponential decay model, forms the basis of policy guidelines and national CDR accounting. However, our re-analysis of the meta-data used in this model reveals significant deficiencies in its parameterization, leading to two critical issues. First, the current parameterization assigns a disproportionally low percentage of the labile carbon fraction (C1) relative to the recalcitrant fraction (C2), effectively reducing the model to a single-pool approach. Due to the limited duration of incubation experiments, the decay constant of the labile fraction is incorrectly applied to the entire biochar mass, resulting in a considerable overestimation of the biochar decay rate. Second, our analysis reveals a lack of causal correlation between the assigned proportions of C1 and C2 and key carbonization parameters such as production temperature and hydrogen-to-carbon (H/C) ratios, suggesting that the model does not accurately represent the underlying chemistry. This misalignment contradicts the established relationship between increased biochar stability and a higher degree of carbonization. Consequently, the parameterization of current model may not adequately reflect the carbon sequestration potential of biochar. While a multi-pool decay model is suitable for predicting the permanence of biochar, the primary issue with the current model lies in its parameterization rather than its structure. To address these limitations, we recommend that future research prioritize the development of a revised multi-pool decay model with improved parameterization, supported by empirical decomposition data from a variety of experimental methods, including incubation studies, accelerated aging experiments, and comprehensive physicochemical characterization. This refined approach will improve the accuracy of biochar permanence estimations, strengthening its role in global carbon management strategies.
Sanei, H. et al. (2025) Evaluating the Two-Pool Decay Model for Biochar Carbon Permanence. 7 (9) Springer Nature.
Read the full paper here: Evaluating the Two-Pool Decay Model for Biochar Carbon Permanence I Springer Nature.
Contrasting CO2 Dynamics in Seagrass Meadows Between Organic Carbon (OC)-Rich Reef and OC-Poor Terrestrial Sediments: Implications for Enhanced Alkalinity Production
Abstract
Seagrass meadows are increasingly recognized across the globe as a natural climate solution due to their significant potential in alkalinity-driven carbon dioxide (CO2) removal, which possibly represents an overlooked component of ocean carbon removal. This study comprehensively investigated the carbonate chemistry, sediment carbon content, mineral composition, and benthic alkalinity fluxes in two distinct sites with tropical seagrass meadows: one situated in organic carbon (OC)-rich reef sediments and the other in OC-poor terrestrial sediments. Results showed nearly two orders of magnitude higher benthic alkalinity fluxes in the OC-rich reefs than in OC-poor sediments (72.8 ± 64.4 vs. 0.53 ± 0.99 mmol m−2 d−1). This can further substantially increase alkalinity levels and reduce the partial pressure of CO2 in the overlying seawater, thereby enhancing the capacity for CO2 uptake. We propose that seagrass meadows on high-OC reef sediments, the hotspots for alkalinity generation, could amplify the climate change mitigation potential of seagrass restoration initiatives.
Chou, W. et al. (2025) Contrasting CO2 Dynamics in Seagrass Meadows Between Organic Carbon (OC)-Rich Reef and OC-Poor Terrestrial Sediments: Implications for Enhanced Alkalinity Production. 52 (4) Geophysical Research Letters.
Read the full paper here: Contrasting CO2 Dynamics in Seagrass Meadows Between Organic Carbon (OC)-Rich Reef and OC-Poor Terrestrial Sediments: Implications for Enhanced Alkalinity Production I Geophysical Research Letters.
Nitrogen Addition Increases the Organic Residue-Induced Carbon Mineralization by Shifting Soil Bacterial and the Fungal Community Structure and Co-Occurrence Network
Abstract
Organic residue plus nitrogen (N) fertiliser is an efficient method for improving agricultural soil quality and yield. However, it also induces organic carbon (C) loss through mineralization. Soil microorganisms are involved in regulating the soil C cycle; however, the microbial community and keystone taxa to regulate organic C mineralization and their underlying factors in orchard remain unclear. To address this, soil samples from apple orchard were collected and amended with wheat straw combined with different levels of N (0 mg kg−1, S; 200 mg kg−1, S + RN; 300 mg kg−1, S + CN; 500 mg kg−1, S + HN), soil without any straw or N as CK, and incubated for 110 days in a laboratory. Wheat straw increased the CO2 efflux rate, especially the N supply, in the following order: S + HN > S + CN > S + RN > S > CK. The cumulative mineralization of organic C (Cmin) under straw addition and straw plus N input were higher than that under CK. At the end of incubation, the straw plus N treatments increased Cmin by 15.02% (S + RN), 20.06% (S + CN), and 32.45% (S + HN) compared with treatment S. Straw plus N increased the relative abundance of Actinobacteria and Chloroflexi but decreased that of Acidobacteria, Myxococcota, and Latescibacterota. The co-occurrence network indicated that the additional N supply led to simpler and less complex microbial networks in soil under wheat straw. The keystone taxa of bacteria, Acidobacteria and Latescibacterota, were negatively correlated with Cmin. Meanwhile, Entotheonellaeota and Actinobacteria of the bacterial phylum and Basidiomycota of the fungal phyla were positively correlated with Cmin. Straw plus N application increased the positive/negative links of fungi. This indicates that the alleviated competitive interactions coupled with keystone taxa in the fungal network dominated the promotion of Cmin. Structural equation model analysis showed that soil bacterial communities and fungal networks were key factors that increased soil enzyme activities and induced organic C mineralization. Wheat straw combined with N fertiliser reduction may be a sustainable strategy for mitigating organic C mineralization in orchard soils.
Lang, D. et al. (2025) Nitrogen Addition Increases the Organic Residue-Induced Carbon Mineralization by Shifting Soil Bacterial and the Fungal Community Structure and Co-Occurrence Network 41 (2) Soil Use and Management.
Read the full paper here: Nitrogen Addition Increases the Organic Residue-Induced Carbon Mineralization by Shifting Soil Bacterial and the Fungal Community Structure and Co-Occurrence Network I Soil Use and Management.
A Comprehensive 5E Analysis of Synthetic Natural Gas Production through Direct Air Capture and Renewable Hydrogen: Based on a Specified-Scale Residential Application
Abstract
Synthetic natural gas (SNG) production through direct air capture (DAC) and renewable hydrogen could be a potential solution to address the scarcity of natural gas resources, reduce CO2 emissions from the atmosphere, enable the storage of renewable energies, and improve sustainable production. In this study, a renewable grid-connected SNG production system is analyzed, based on DAC technology and green hydrogen as input feedstock, to meet the natural gas consumption needs of a specified-scale residential application year-round. This energy system incorporates a wind farm as a renewable energy supplier to support hydrogen production and CO2 absorption in the methanation process for a residential application in Sankhast city, North Khorasan, Iran. The aim of this research is to present significant findings regarding the implementation of such a system in Iran, assisting engineers in testing and applying it under real conditions. To analyze the system dynamically from energy, exergy, exergoeconomic, economic, and environmental (5E) perspectives, Aspen Plus and EES software were utilized for modeling and simulation. Additionally, the TOPSIS method, a multi-criteria decision-making approach, was employed to perform multi-objective optimization of the SNG production process and the capacity of renewable wind power. The results revealed that the system produced high-quality SNG with 98.7 % methane purity while addressing SNG shortages during peak months by storing excess SNG produced during hotter months, with the highest storage capacity of 13.5 km3 reported in July. Furthermore, the system achieved energy and exergy efficiencies of 31.17 % and 18.1 %, respectively, and sold the highest excess power of 1240 MWh in July. In the economic analysis, the highest cost was attributed to investment, with the levelized cost of energy (LCOE) reported at 8.65 $/kWh, where the purchase of wind turbines represented the largest expenditure. Finally, environmental analysis reported that the system could potentially reduce CO2 emissions by 1540 tons annually.
Sami, S. et al. (2025) A Comprehensive 5E Analysis of Synthetic Natural Gas Production through Direct Air Capture and Renewable Hydrogen: Based on a Specified-Scale Residential Application. 212 (115376) Renewable and Sustainable Energy Reviews.
Read the full paper here: A Comprehensive 5E Analysis of Synthetic Natural Gas Production through Direct Air Capture and Renewable Hydrogen: Based on a Specified-Scale Residential Application I Renewable and Sustainable Energy Reviews.