This week’s publication highlights cover a number of issues such as the use of triethanolamine solution for CDR and CDR potential of temperate macroalgal forests as well as other matters pertaining to direct air capture, afforestation, bioenergy with carbon capture and storage and enhanced rock weathering.
Carbon Dioxide Removal from Triethanolamine Solution Using Living Microalgae-Loofah Biocomposites
Abstract
Nowadays, the climate change crisis is an urgent matter in which carbon dioxide (CO2) is a major greenhouse gas contributing to global warming. Amine solvents are commonly used for CO2 capture with high efficiency and absorption rates. However, solvent regeneration consumes an extensive amount of energy. One of alternative approaches is amine regeneration through microalgae. Recently, living biocomposites, intensifying traditional suspended cultivation, have been developed. With this technology, immobilizing microalgae on biocompatible materials with binder outperformed the suspended system in terms of CO2 capture rates. In this study, living microalgae-loofah biocomposites with immobilized Scenedesmus acuminatus TISTR 8457 using 5%v/v acrylic medium were tested to remove CO2 from CO2-rich triethanolamine (TEA) solutions. The test using 1 M TEA at various CO2 loading ratios (0.2, 0.4, 0.6, and 0.8 mol CO2/mol TEA) demonstrated that the biocomposites achieved CO2 removal rates 3 to 5 times higher than the suspended cell system over 28 days, with the highest removal observed at the 1 M with 0.4 mol CO2/mol TEA (4.34 ± 0.20 gCO2/gbiomass). This study triggers a new exploration of integration between biological and chemical processes that could elevate the traditional amine-based CO2 capture capabilities. Nevertheless, pilot-scale investigations are necessary to confirm the biocomposites’s efficiency.
Komkhum, T. et al. (2025) Carbon Dioxide Removal from Triethanolamine Solution Using Living Microalgae-Loofah Biocomposites. 7247 (15) Scientific Reports.
Read the full paper here: Carbon Dioxide Removal from Triethanolamine Solution Using Living Microalgae-Loofah Biocomposites I Scientific Reports.
Carbon dioxide removal (CDR) potential in temperate macroalgal forests: A comparative study of chemical and biological net ecosystem production (NEP)
Abstract
The carbon dioxide removal (CDR) capacity of macroalgae, a crucial component in climate regulation, has gained increasing attention. However, accurately estimating the CDR potential of macroalgae in natural conditions remains challenging, necessitating the use of multiple independent methods to reduce the uncertainties in these estimates. In this study, we compared two methods for estimating net ecosystem production (NEP), a key parameter in determining CDR potential: 1) NEPChem., derived from seawater carbonate chemistry and 2) NEPBiol., based on photorespiratory measurements using benthic tent incubation. This study, conducted in a macroalgal forest dominated by Ecklonia cava, involved simultaneous measurements of NEPChem. and NEPBiol. over a course of one year. Our findings revealed that NEPBiol. was 1.23 times higher than NEPChem., with an annual rate of 3.69 tons CO2 ha−1 yr−1. These results suggest that both independent methods are reliable and can be used complementarily to improve the accuracy of NEP measurements, thereby enhancing estimates of the CDR potential of macroalgae.
Kim, J. et al. (2025) Carbon dioxide removal (CDR) potential in temperate macroalgal forests: A comparative study of chemical and biological net ecosystem production (NEP). Marine Pollution Bulletin 117327 (210).
Read the full paper here: Carbon dioxide removal (CDR) potential in temperate macroalgal forests: A comparative study of chemical and biological net ecosystem production (NEP) I Marine Pollution Bulletin.
Carbonation of MgO Single Crystals: Implications for Direct Air Capture of CO2
Abstract
Direct air capture (DAC) may be feasible to remove carbon dioxide (CO2) from the atmosphere at the gigaton scale, holding promise to become a major contributor to climate change mitigation. Mineral looping using magnesium oxide (MgO) is potentially an economical, efficient, and sustainable pathway to gigaton-scale DAC. The hydroxylation and carbonation of MgO determine the efficiency of the looping process, but their rates and mechanisms remain uncertain. In this work, MgO single crystals were reacted in air or CO2 at varying humidities and characterized by X-ray scattering, microscopy, and vibrational spectroscopy. Results show that the hydroxylation formed a brucite (Mg(OH)2)-like layer immediately after crystal cleaving. Concurrently, the carbonation formed hydrated magnesium carbonate phases, including barringtonite (MgCO3·2H2O) and nesquehonite (MgCO3·2H2O), in the layer. Rapid initial growth of the layer is also manifested in short-range bending/warping of nanocrystallites, resulting in multiple orientations of the same phases on the surface. The layer growth slowed down over time, indicating surface passivation. The formation of barringtonite and nesquehonite with 1:1 CO3/Mg ratio indicates an efficient carbonation when compared to other magnesium carbonate phases of lower ratio. Our results are essential for understanding surface passivation mechanisms and tackling the passivation issue of mineral looping DAC technology.
Yang, P. et al. (2025) Carbonation of MgO Single Crystals: Implications for Direct Air Capture of CO2. 59 (7) Environmental Science & Technology.
Read the full paper here: Carbonation of MgO Single Crystals: Implications for Direct Air Capture of CO2 I Environmental Science & Technology.
Earth System Modeling-Based Comparison between Afforestation and Bioenergy with Carbon Capture and Storage
Abstract
Afforestation and bioenergy with carbon capture and storage (BECCS) are two typical land-based carbon dioxide removal strategies to combat climate change. We use life cycle assessment (LCA)-integrated Earth system modeling to compare their carbon sequestration efficiencies and associated environmental impacts. The results show that, for achieving the same 0.1 ℃ global cooling effect by year 2099 under a business-as-usual emission scenario, around 101 to 226 GtC (gigatonnes of carbon) need to be bio-assimilated on land via afforestation cumulatively, while BECCS demands 21.55 to 79.47 GtC to be extracted from vegetation carbon pool to produce bioelectricity. Our study confirms the relatively higher carbon dioxide removal potential of BECCS compared to afforestation and highlights the value of using the LCA-integrated Earth system modeling method to investigate the large-scale climate mitigation practices.
Qi, X. and Feng, E. (2025) Earth System Modeling-Based Comparison between Afforestation and Bioenergy with Carbon Capture and Storage. ESS Open Archive.
Read the full paper here: Earth System Modeling-Based Comparison between Afforestation and Bioenergy with Carbon Capture and Storage I ESS Open Archive.
Are Enhanced Rock Weathering Rates Overestimated? A Few Geochemical and Mineralogical Pitfalls
Abstract
There is considerable uncertainty when quantifying carbon dioxide removal (CDR) from enhanced rock weathering (ERW). Faster CDR rates mean ERW may significantly impact climate change mitigation, and more carbon credits will financially benefit private companies. However, overestimating CDR risks undermining ERW if meaningless carbon credits are counted. Here, we aim to contribute to the discussion of CDR quantification by describing three potential pitfalls relating to the geochemical and mineralogical compositions of rock powders. First, rock powders used for ERW are often mineralogically complex and may initially exhibit fast dissolution rates due to reactive surfaces and phases, leading to overestimating long-term CDR rates. Second, the dissolution of accessory carbonates within ERW rock powders will tend to dominate cation and dissolved inorganic carbon fluxes, which, if not identified, can be misconstrued as silicate weathering and overestimate CDR. Third, methods that rely on measuring cations may be prone to misinterpretation as cations will often not be balanced with dissolved inorganic carbon, e.g., during strong acid weathering. As another example, mineral dissolution during solid-phase testing (e.g., cation exchange) is also unrelated to carbonic acid weathering and, thus, may overestimate CDR rates. To avoid these pitfalls, we recommend (1) incorporating high-dosage test plots into ERW trials that avoid reapplication of rock powders that replenish initially fast reactivity, (2) screening rock powders for carbonate minerals using sensitive techniques and distinguishing carbonate and silicate weathering, and (3) measuring carbon to verify carbon dioxide removal. High-quality carbon credits must be durable, additional, and not overestimated.v
Power, I. et al. (2025) Are Enhanced Rock Weathering Rates Overestimated? A Few Geochemical and Mineralogical Pitfalls. 6 Frontiers.
Read the full paper here: Are Enhanced Rock Weathering Rates Overestimated? A Few Geochemical and Mineralogical Pitfalls I Frontiers.