This week’s publication highlights relate to enhanced weathering, optimization of engineered CDR technologies, negative emission waste-to-concrete, biochar carbon removal and direct air capture.
Higher Inorganic CO2 Removal Despite Slower Weathering in an Enhanced Weathering Experiment with Steel Slags and Basalt
Abstract
The natural process of silicate weathering has inspired two CO2 removal technologies: enhanced weathering and mineral carbonation. Here, in a 15-month mesocosm experiment, both approaches were combined, with the aim of maximising CO2 removal. To do so, pre-carbonated steel slags (basic oxygen furnace (BOF) and argon oxygen decarburisation (AOD) slag) with mineral carbonation rates ranging from 0.04 to 0.13 t CO2/t rock were applied to soil planted with maize. Other treatments included uncarbonated slags and basalt for comparison. Aside from the commonly assessed leachate and soil solid carbonate pool, which contribute to inorganic CO2 removal, also other soil pools (plant, exchangeable, (hydr)oxide, SOM) not directly linked to CO2 removal were assessed. These alternative sinks are key to better understand the low inorganic CO2 removal efficiencies reported in many experiments. Indeed, also in this experiment, the realised inorganic CO2 removal of enhanced weathering remained low in all treatments (< 0.014 t CO2/t rock), except for the highest carbonated slag treatment, which removed slightly more CO2 (0.04 t CO2/t rock). Thus, with a high degree of prior mineral carbonation, the inorganic CO2 removal during enhanced weathering was increased. This was the case even though carbonated slags weathered slower. These results demonstrate that active weathering does not necessarily imply high inorganic CO2 removal. While slags weathered almost entirely after only 4 months, less than 5.3% of the theoretical possible CO2 removal was realised. If weathering occurred too rapidly, the formation of secondary minerals such as (hydr)oxides and/or aluminosilicate clays likely immobilised base cations, thereby constraining inorganic CO2 removal. For uncarbonated slags, ~58% (BOF) and 70% (AOD) of the added base cations were likely locked in (hydr)oxides/aluminosilicate clays. These findings underline that understanding the fate of weathering products (beyond the leachate and carbonate pool) is key to assess the ‘true’ inorganic CO2 removal potential of enhanced weathering.
Steinwidder, L. et al. (2026) Higher Inorganic CO2 Removal Despite Slower Weathering in an Enhanced Weathering Experiment with Steel Slags and Basalt 32 (1) Global Change Biology.
Read the full paper here: Higher Inorganic CO2 Removal Despite Slower Weathering in an Enhanced Weathering Experiment with Steel Slags and Basalt I Global Change Biology.
Achieving Carbon Neutrality in Northwest China through Economically and Environmentally Sustainable Optimization of Negative Emission Technologies
Abstract
The large-scale deployment of negative emission technologies (NETs) is critical for achieving carbon neutrality, but identifying an optimal portfolio that balances economic and environmental sustainability remains a challenge. In this study, a multi-objective model is proposed to identify the optimal NETs portfolio in Northwest China, a region characterized by energy wealth and ecological vulnerability. The developed model aims to simultaneously maximize the economic returns while minimizing environmental footprints, including land, water, energy, nitrogen, and phosphorus consumption. A dual discount rate framework, incorporating both economic and environmental discount rates, is established to analyze the tradeoffs between economy and environment. Results indicate that biochar is the most effective NET and dominates the technology portfolio before 2035. Conversely, bioenergy with carbon capture and storage shows limited effectiveness and sustainability due to its high environmental footprints. In the long term (post-2035), enhanced weathering and direct air carbon capture and storage become essential for achieving deep decarbonization and eventual carbon neutrality. Furthermore, results also reveal that higher economic and environmental discount rates promote the early deployment of NETs but result in a lower economic return and a larger environmental footprint, highlighting a trade-off between short-term action and long-term sustainability. These results provide useful information for formulating optimal NETs deployment strategies and underscore the necessity of incorporating long-term environmental concerns into policy-making to ensure the sustainable achievement of carbon neutrality.
Suo, C. et al. (2026) Achieving Carbon Neutrality in Northwest China through Economically and Environmentally Sustainable Optimization of Negative Emission Technologies 22 (7) Discover Sustainability.
Read the full paper here: Achieving Carbon Neutrality in Northwest China through Economically and Environmentally Sustainable Optimization of Negative Emission Technologies I Discover Sustainability
Negative-Emission Waste-to-Concrete via Tandem Supercritical Water Oxidation and Hydrothermal Mineralization
Abstract
Concrete production and municipal solid waste management contribute up to 13% of global CO2 emissions. Here, we describe Hydrothermal Oxidation and Mineralization (HTOM) as a new process for production of alternative construction material (ACM) with a compressive strength (9.23 ± 0.98 MPa) more than double what is required for non-loadbearing concrete (4.14 MPa) while storing CO2. HTOM consists of two oxidative reactions: (1) supercritical water oxidation (SCWO) converts the organic fraction of food waste to a high-pressure CO2 stream while producing thermal bioenergy that can be recovered using a turbine, then (2) the high-pressure CO2 stream is used for rapid mineralization of soluble calcium to calcium carbonate, reaching 100% conversion within 20 minutes. ASPEN/HYSYS simulations and a GREET lifecycle analysis demonstrate that HTOM has the potential to offset 0.1 kg of CO2 per kg of ACM produced by simultaneously diverting fugitive landfill emissions, capturing waste energy, and offsetting traditionally CO2-intensive concrete mortar production.
Kenney, D. et al. (2026) Negative-Emission Waste-to-Concrete via Tandem Supercritical Water Oxidation and Hydrothermal Mineralization 4 RSC Sustainability.
Read the full paper here: Negative-Emission Waste-to-Concrete via Tandem Supercritical Water Oxidation and Hydrothermal Mineralization I RSC Sustainability.
Comprehensive Evaluation of the Hydrology, Pollutant Removal, and Carbon Sequestration Performance of Biochar-Enriched Bioretention Soil
Abstract
Low impact development (LID) systems effectively reduce stormwater runoff and improve water quality. In addition, their potential contributions to carbon sequestration and climate change adaptation have attracted growing research attention. This study investigated the influence of biochar content on the performance of bioretention cells. A series of experiments was conducted to evaluate eight key indicators: saturated hydraulic conductivity (Ksat), water holding capacity, removal efficiencies for ammonium nitrogen (NH4-N), nitrate nitrogen (NO₃-N), phosphate (PO43−-P), and chemical oxygen demand (COD); CO2 sequestration flux; and soil organic carbon content. The results indicate that biochar amendments significantly improve the functionality of LID systems. Furthermore, the addition of 2.5 % biochar effectively enhances soil hydrological properties, creating favorable conditions for plant growth. The addition of 5 % biochar results in optimal pollutant removal and water purification, thus serving as a well-balanced and efficient treatment strategy. Moreover, the addition of 10 % biochar results in optimal carbon sequestration, demonstrating the role of biochar in strengthening soil carbon sinks. However, excessive biochar content may affect microbial activity and nutrient pathways, potentially leading to reductions in NO3-N and COD removal efficiencies. This study provides practical guidance for optimizing biochar use in LID systems to support stormwater management, water quality improvement, and long-term climate mitigation through soil-based carbon storage.
Hu, C. et al. (2026) Comprehensive Evaluation of the Hydrology, Pollutant Removal, and Carbon Sequestration Performance of Biochar-Enriched Bioretention Soil 1011 (181174) Science of the Total Environment.
Read the full paper here: Comprehensive Evaluation of the Hydrology, Pollutant Removal, and Carbon Sequestration Performance of Biochar-Enriched Bioretention Soil I Science of the Total Environment.
Accelerating Widespread Adoption of Direct Air Capture based on System Perspective: Thermodynamic Limits, Geographical Deployment, and Clear Energy Integration
Abstract
Direct Air Capture (DAC) is a critical negative emission technology essential to achieve the global climate targets. However, its widespread adoption is hindered by a multitude of technical, economic, deployment, and sustainability challenges. The purpose of this review is to bridge this critical gap by deconstructing the challenges and opportunities for DAC through a novel, three-tiered analytical framework. Basically, the fundamental challenge of DAC lies in the high energy consumption and low exergy efficiency associated with CO2 enrichment from its low atmospheric concentration. Analysis suggests that the thermodynamic limits of different DAC pathways, which dictate their theoretical energy consumption, are the primary determinants of their technological maturity and potential for large-scale development. From the perspective of geographical deployment, the idealized notion of placing DAC facilities anywhere is unfeasible due to practical, location-specific constraints. Combining large-scale centralized hubs with agile distributed units is a critical enabler for achieving diversified and efficient deployment. Furthermore, as the environmental benefits of DAC are critically dependent on the availability of clean energy, effective integration with the energy system is paramount. The argument of this review is that DAC, when combined with CO2 utilization and storage and powered by clean energy, may hold distinct advantages over Bioenergy with Carbon Capture and Storage (BECCS) in terms of theoretical removal potential and resource sustainability, presenting a fundamental opportunity for DAC to become a true negative carbon solution. By providing such a holistic synthesis, our work establishes a strategic roadmap for prioritizing research, investment, and policy, transforming the discourse from isolated technical problems to a cohesive system-engineering challenge.
Li, C. et al. (2026) Accelerating Widespread Adoption of Direct Air Capture based on System Perspective: Thermodynamic Limits, Geographical Deployment, and Clear Energy Integration 230 (116702) Renewable and Sustainable Energy Reviews.
Read the full paper here: Accelerating Widespread Adoption of Direct Air Capture based on System Perspective: Thermodynamic Limits, Geographical Deployment, and Clear Energy Integration I Renewable and Sustainable Energy Reviews.