Negative Emissions Research Articles

Biochar from agricultural wastes: Environmental sustainability, economic viability and the potential as a negative emissions technology in Malaysia

Biochar used for soil amendment is considered a viable negative emissions technology as it can be produced easily from a wide range of biomass feedstocks, while offering numerous potential agricultural benefits. This research is the first to present a comprehensive sustainability assessment of large-scale biochar production and application in Malaysia. The five feedstocks considered comprise the country's most abundant agricultural wastes from palm oil (empty fruit bunches, fibres, palm fronds and shells) and rice (straw) plantations. Combined with process simulation, life cycle assessment and life cycle costing are used to assess the sustainability of biochar production via slow pyrolysis at different temperatures (300–600 °C), considering two functional units: i) production and application of 1 t of biochar; and ii) removal of 1 t of CO2from the atmosphere. The cradle-to-grave system boundary comprises all life cycle stages from biomass acquisition to biochar use for soil amendment. The positive impacts of the latter, such as carbon sequestration, fertiliser avoidance and reduction in soil N2O emissions, are also included. The global warming potential (GWP) is net-negative in all scenarios, ranging from −436 to −2,085 kg CO2 eq./t biochar and −660 to −933 kg CO2 eq./t CO2 removed. Per t of biochar, the systems with shells have the lowest GWP and those with straw the highest, all showing better performance if produced at higher pyrolysis temperatures. However, the temperature trend is opposite for all other 17 impacts considered, with fibres being the best option and fronds the worst for most categories. Per t CO2 removed, fronds have the highest impact in eight categories, including GWP, and shells the lowest in most categories. All impacts are lower for biochar production at higher temperatures. The main hotspot is the pyrolysis process, influencing the majority of impact categories and contributing 66–75 % to the life cycle costs. The costs range from US$116–197/t biochar and US$60–204/t CO2 removed. The least expensive systems per t biochar are those with straws and per t CO2 removed those with shells, while fronds are the worst option economically for both functional units. Utilising all available feedstocks could remove 6–12.4 Mt of CO2 annually, reducing the national emissions from the agricultural sector by up to 54 % and saving US$36.05 M annually on fertilisers imports. These results will be of interest to policy makers in Malaysia and other regions with abundant agricultural wastes.

Analysing the response of CO2 emissions to business cycle in a developing economy: evidence for South Africa post-apartheid era

Introduction: This research addresses the response of CO2 emissions to economic fluctuations in South Africa post-Apartheid, covering the period 1990–2018. While previous studies focused on developed countries, limited attention has been given to sub-Saharan developing nations. The study challenges the assumption of constant emissions elasticity in current forecasts.Methods: The study employs a two-step strategy. Firstly, the rolling window regression with Hodrick-Prescott filtering was used to investigate whether the CO2 emissions elasticity varies over time. Secondly, a Markov-switching approach was used to examine the regime-switching behavior in GDP.Results and Discussion: Results suggest that CO2 emisssions elasticity varies over time. This was confirmed through alternative filtering techniques (Christiano-Fitzgerald, Baxter King, and the Butterworth filter). Markov-switching analysis revealed a regime-switching behavior in GDP, indicating negative CO2 emissions elasticity during recessions and positive elasticity during expansions. These findings persist even when accounting for monetary policy shocks and productivity shocks in the Environmental Dynamic Stochastic General Equilibrium (E-DSGE) model. Noteworthy is that South Africa is among the top 20 greenhouse gas emitters globally.Conclusion and recommendations: The study recommends tailored carbon-pricing policies that are conscious to the countercyclical nature of business cycles. Pricing emissions higher during economic upswings aligns with periods of growth. Additionally, the government is advised to invest in research and development for energy conservation, efficiency, and renewable technologies to counterbalance emissions growth. Implementing emission caps and tax incentives can further enforce pollution abatement measures. Policymakers should consider these asymmetrical responses when addressing global warming challenges in South Africa.

One step closer: Laypeople’s perception of production steps for manufacturing CO2-based jet fuel

BackgroundThe need for greenhouse gas abatement measures grows as climate change threatens life on earth. Negative emission technologies, such as carbon capture and utilization (CCU), can reduce emissions from the transport sector, particularly aviation. However, the lack of support and low public acceptance can impact the successful introduction of new technologies. This study analyzes the factors that influence acceptance of the single production steps (capture, purification, conversion, and transport of CO2) of production of CO2-based jet fuels to identify acceptance hot spots and potential roll-out barriers.ResultsIn a quantitative survey with n = 543 German respondents, we find that transport of CO2 in comparison with capture, purification, and conversion of CO2 into hydrocarbons is perceived as less acceptable, efficient, and useful, more expensive as well as damaging for the environment and health. Furthermore, product-step specific risk perceptions, as well as benefit and barrier perceptions for CCU mainly predict people’s attitude towards the four production steps. A cluster-analysis revealed two groups, “Approvers” and “Sceptics”, which were characterized by distinctive perception profiles. Further analysis showed that sustainability (e.g., use of renewable energy) and efficiency (e.g., carbon removal and resource use) were of greater importance to Approvers.ConclusionsThe study’s results suggest the need for further research and information provision to enhance public understanding of the technology and its role as a part of circular economy approaches. Risk perceptions play a central role in determining attitudes towards CCU, which should be considered in future studies and communication strategies. The findings can inform policymakers, industry stakeholders, and communication experts working to promote sustainable aviation fuel technologies.

Whose negative emissions? Exploring emergent perspectives on CDR from the EU's hard to abate and fossil industries

Net zero targets have rapidly become the guiding principle of climate policy, implying the use of carbon dioxide removal (CDR) to compensate for residual emissions. At the same time, the extent of (future) residual emissions and their distribution between economic sectors and activities has so far received little attention from a social science perspective. This constitutes a research gap as the distribution of residual emissions and corresponding amounts of required CDR is likely to become highly contested in the political economy of low-carbon transformation. Here, we investigate what function CDR performs from the perspective of sectors considered to account for a large proportion of future residual emissions (cement, steel, chemicals, and aviation) as well as the oil and gas industry in the EU. We also explore whether they claim residual emissions to be compensated for outside of the sector, whether they quantify these claims and how they justify them. Relying on interpretative and qualitative analysis, we use decarbonization or net zero roadmaps published by the major sector-level European trade associations as well as their statements and public consultation submissions in reaction to policy initiatives by the EU to mobilize CDR. Our findings indicate that while CDR technologies perform an important abstract function for reaching net zero in the roadmaps, the extent of residual emissions and responsibilities for delivering corresponding levels of negative emissions remain largely unspecified. This risks eliding pending distributional conflicts over residual emissions which may intersect with conflicts over diverging technological transition pathways advocated by the associations.

China's energy-water-land system co-evolution under carbon neutrality goal and climate impacts

China's 2060 carbon neutrality goal has significant implications for energy, water, and land systems. However, the multi-sector dynamics among China's energy-water-land system have rarely been examined explicitly. This study adopts an integrated assessment framework to simulate China's energy-water-land system co-evolution under alternative carbon neutrality scenarios and climate impacts. Results show that although the net zero emission target provides the incentive for the energy system to move away from fossil fuels, total water withdrawal will increase due to the deployment of nuclear, bioenergy, and coal power plants with carbon capture and storage. Diversifying the negative emission technologies, by leveraging direct air capture technology, can alleviate the potential water stress and land use conflicts, which would otherwise be exacerbated by large-scale deployment of afforestation and bioenergy with carbon capture and storage. Northwest and northeast regions of China are the hotspots experiencing water withdrawal increases, while Bohai Rim and coastal regions are identified to experience fierce land competition. This study demonstrates the potential for general applicability to carry out resource planning and policy evaluation from the multi-sector coordination perspective.

Evaluation of microalgae biodiesel for carbon neutrality based on the waste treatment by the autotrophic and heterotrophic combination

Microalgae aid in addressing environmental pollution and climate change by enabling carbon sequestration as part of CCUS, which offers a promising solution to reduce fossil fuel dependence and mitigate emissions. This study uses the combination of autotrophic and heterotrophic methods to enhance the benefits of biodiesel based on waste treatment. The study demonstrates that by integrating autotrophic and heterotrophic biodiesel production, it is feasible to attain substantial economic advantages while maximizing carbon sequestration and reducing emissions. It shows a 62.73 % cost reduction for 1 ton of biodiesel produced using the coupled heterotrophic method over traditional photobioreactors. Additionally, compared with the corresponding heterotrophic proliferation, the carbon emissions of biodiesel under autotrophic coupled heterotrophic proliferation were reduced by 21.16 % and 24.08 %, respectively. The total economic benefits of biodiesel under autotrophic coupled heterotrophic proliferation increased by 2.12 % and 3.10 % compared to heterotrophic proliferation. However, it should be noted that due to the high carbon emissions caused by the heterotrophic proliferation of microalgae, biodiesel does not achieve negative carbon emissions. This study provides a new development strategy for waste resource utilization and microalgae bioenergy production phase. It will provide a theoretical and practical framework for utilizing microalgae biodiesel to achieve worldwide carbon neutrality.

CuxMg1-xFe2O4-type spinels as potential oxygen carriers for waste wooden biomass combustion

Waste wood biomass is considered a renewable energy source. Combining biomass combustion with emerging clean combustion technologies such as chemical looping combustion (CLC) can yield effective and affordable carbon capture and, consequently, lead to negative net emissions of greenhouse gases. Oxygen carrier (OC) is a crucial material in CLC technology that must exhibit certain properties, such as high durability, good chemical stability during numerous red-ox cycles and, important for the combustion of solid fuels, the capability of spontaneously releasing oxygen in a process referred to as chemical looping with oxygen uncoupling (CLOU). In this work, a series of nine CuxMg1-xFe2O4 spinel-based materials were synthetized and evaluated for the first time as potential OCs for a waste biomass combustion. Their properties, such as oxygen transport capacity and reactivity with biomass (wood chips) as a fuel, were evaluated in a function of temperature (900–1000 °C). Tested oxygen carriers were characterized with an excellent oxygen transport capacity in CLOU process (up to 2.78 wt%) and good reaction rates with the fuel (up to 1.19 wt. %/min), and regeneration rates (up to 3.8 wt. %/min). High conversion of the waste biomass was also achieved (98.9 %). Moreover, new findings revealed a strong positive effect of magnesium addition on mechanical strength (crushing strength > 4 N for samples with Mg content above 0.5).

Analysis of the Multiphase Flow With Condensation in the Two-Phase Ejector Condenser Using Computational Fluid Dynamics Modeling

Abstract The liquid-driven two-phase ejector condenser is the object of the numerical investigation. The spray-ejector condenser is one of the critical components of the developed gas power plant with negative CO2 emission. The task of the ejector is to entrain exhaust gas and condense steam contained in it. Computational fluid dynamics (CFD) modeling allows analyzing complex phenomena and predicting the influence of a wide range of operating parameters on the local structure of the multiphase flow with condensation. The geometrical model of the ejector was designed to provide efficient steam condensation and generate sub-pressure region at the gas inlet. The 2D, axisymmetric CFD model was created using simcenter star ccm+ software. The multiphase mixture model was used to take into account two-phase flow. Turbulent flow was computed using k–ω SST model. Direct contact condensation of steam was calculated using two different approaches: the Spalding/evaporation model and the thermally-driven boiling/condensation model. The influence of various gas inlet velocities and the presence of CO2 on the operation of the ejector condenser were investigated based on scalar fields and charts representing changes in the most important variables along the flow path. The condensation is the most intense in the suction chamber. The boiling/condensation model predicts lower suction pressure and higher condensation effectivity than Spalding/evaporation model. The CO2 considerably affects the pressure and temperature distributions and reduces the condensation rate.

Exploratory Review on Environmental Aspects of Enhanced Weathering as a Carbon Dioxide Removal Method

The accumulation of carbon dioxide in the atmosphere due to fossil fuel burning and deforestation has caused global warming and an increase in extreme weather events. To complement the shift towards clean energy, it is crucial to adopt methods for carbon dioxide removal, known as negative emission technologies. Enhanced weathering is one such approach that involves accelerating the natural process of rock weathering by spreading finely ground rocks over large areas, such as agricultural land or coastal areas. This exploratory review paper provides an overview of the fundamental mechanisms behind enhanced weathering, and outlines the techniques for its implementation. The environmental benefits of enhanced weathering are highlighted, including carbon dioxide removal, and improvement of soil fertility. Furthermore, potential impacts on ecosystems and biodiversity are examined, along with the effects on water, soil and air quality. The paper also considers the risks and challenges associated with large-scale implementation and long-term stability of enhanced weathering. Additionally, the integration of enhanced weathering with Sustainable Development Goals is explored, along with the potential co-benefits and trade-offs with other sustainability objectives. To conclude, this exploratory review paper summarizes the key findings and proposes avenues for further research in this field of enhanced weathering.

Techno-economic assessment of the CO2 value chain with CCUS applied to a waste-to-energy Italian plant

Recently, post-combustion CO2 removal has been considered also for the CO2 separation from the flue gases of Waste-to-Energy (WtE) plants, that manage high amounts of Municipal Solid Waste (MSW) by combusting it and generating power and heat. Moreover, because of the presence in MSW of an organic waste fraction, net negative CO2 emissions are feasible when integrating CCUS systems into WtE plants. Currently, to the best of the authors’ knowledge, there are only few incineration plants around the world that are successfully coupled with a carbon capture system, resulting in near-zero (or even negative) CO2 emission power generation.This work focuses on the evaluation of the whole value chain of the non-biogenic CO2 that is emitted in a power plant located in Northern Italy and on its possible utilization, from the CO2 source in the flue gas to the market-ready product.The design of the process for the CO2 removal from the flue gas has been carried out specifically for the considered flue gas to be treated with an aqueous solution of MonoEthanolAmine 30% wt., the benchmark solvent used in other types of power plants (fuelled by coal and natural gas). The main process parameters (e.g., lean loading, absorber packing height, regenerator packing height, regenerator pressure, gas inlet temperature, solvent inlet temperature) have been selected in order to optimize the reboiler duty and the water requirement, the latter being usually not considered in literature works dealing with this type of analysis. Then, the CO2 utilization has been evaluated, considering the options of both sequestration in the Adriatic Sea and utilization of CO2 for production of sodium bicarbonate, on the basis of the information available in the literature.In compliance with Directive 2003/87/EC and with the Italian legislation, Waste-to-Energy plants that treat municipal solid waste are currently exempt from the application of the CO2 Emissions Trading System (ETS). This article speculates about the application of the ETS to an urban WtE plant, located in Northern Italy, and evaluates its economic implications by comparing the purchase of emission quotas with the construction of a CCS or CCU plant.A business plan, detailing the obtained revenues from the utilization and from the avoided cost of purchasing emission allowances and the expenses related to the operation of the carbon capture plant, taking into account the taxes and the inflation, has been created and used for comparing the two considered CO2 value chains. For the option of CO2 sequestration, sensitivity analyses on the variation of investment costs (+10 %), operating costs (+10 %) and revenues (−10 %) have been performed and the breakeven value of the ETS certificate that can make the Net Present Value (NPV) non-negative has been determined. For the option of CO2 utilization, the revenue from sodium bicarbonate that can make its production profitable has been evaluated.

A robust investment decision to deploy bioenergy carbon capture and storage—exploring the case of Stockholm Exergi

The upscaling of novel carbon dioxide removal, such as bioenergy carbon capture and storage (BECCS), to gigatonne scales is an urgent priority if global warming is to be limited to well below 2 °C. But political, economic, social, technological, environmental and regulatory uncertainty permeates BECCS projects and deters investors. To address this, we explore options to improve the robustness of BECCS deployment strategies in the face of multi-dimensional uncertainties. We apply Dynamic Adaptive Planning (DAP) through expert interviews and Robust Decision Making (RDM) through exploratory modelling, two decision making under deep uncertainty methods, to the case of Stockholm Exergi, an early mover aiming to deploy BECCS at a combined heat and power plant in the capital of Sweden. The main contributions of the research are to 1) illustrate how a quantification of robustness against uncertainty can support an investment decision to deploy BECCS 2) comprehensively cover uncertain vulnerabilities and opportunities of deploying BECCS, and 3) identify critical scenarios and adaptations to manage these uncertainties. The main conclusions are: investing in BECCS is relatively robust if assessing performance across many scenarios and if comparing the worst-cases of either investing, or not doing so. Not investing could miss out on up to € 3.8 billion in terms of net present value. The critical uncertainties of BECCS can be managed by strengthening biomass sustainability strategies and by gaining support for negative emission trading regulation on carbon markets, e.g., voluntary or Paris Agreement Article 6. Even in vulnerable scenarios of average electricity prices above 82 €/MWh, if trading regulation is implemented before 2030 and if negative emission prices exceed 151 €/CO2, investing in BECCS performs better than not doing so in 96% of cases. We suggest that facility-level parameters and cost-reductions are of little importance for BECCS investments and upscaling. It is regulatory certainty of operating revenues, e.g., through negative emission markets, that needs to be provided by policymakers.

Integrated Electrochemical Carbon Capture and Utilization by Redox‐Active Amine Grafted Gold Nanoparticles

AbstractElectrochemical carbon capture and utilization (eCCU) from flue gas CO2 could avoid high energy consumption and capital input in conventional capture, storage, and utilization, which is a promising approach for achieving negative emissions and producing “e‐chemicals.” However, low CO2 concentration and leftover O2 in the flue gas presumably lowers the eCCU performance. Herein, redox‐active 2‐amino‐5‐mercapto‐1,3,4‐thiadiazole (AMT) functionalized gold nanoparticles are synthesized to achieve integrated electrochemical capture and reduction of CO2 in simulated flue gas (SFG, 15% CO2, 4% O2, balanced with N2), achieving maximum CO Faradaic efficiency of 80.2% at −0.45 V versus RHE in H‐type cell, and 66.0% at voltage of 2.7 V in a full cell, respectively. The AMT ligand can capture CO2 by strong interaction with CO2 in the reduced state and serve as a selective layer to suppress O2 reduction, which provides the ability of electrochemical carbon capture from SFG and significantly decreases energy required for CO2 electro‐reduction.

Study on emission factor and reduction potential of organic solid waste gasification process

This paper conducts an in-depth study on the gasification treatment of Organic Solid Waste (OSW) and its carbon emissions, intending to fill the gap in the existing literature regarding the calculation methods for carbon emissions from OSW gasification. The study establishes a methodology for calculating carbon emission factors during the OSW gasification process and explores the potential for negative carbon emissions. For this purpose, indicator including the Carbon Dioxide Equivalent Warming Number (CEWN) is used to assess the greenhouse gas emissions of the gasification process by calculating carbon emission factors under different gasification conditions. It is found that within a certain range, increasing the gasification temperature, Equivalence Ratio (ER), and Steam to Biomass ratio (S/B) can positively influences the achievement of negative carbon emissions. These findings hold significant implications for optimizing the OSW gasification process, reducing carbon emissions, and ultimately achieving carbon neutrality. Furthermore, this study fills a critical void in the gasification field within the IPCC framework and offers essential guidance for promoting to achieve peak carbon emissions in the gasification industry and accelerating the goal of carbon neutrality.

Enzyme-accelerated CO2 capture and storage (CCS) using paper and pulp residues as co-sequestrating agents.

In the present work, four CaCO3-rich solid residues from the pulp and paper industry (lime mud, green liquor sludge, electrostatic precipitator dust, and lime dregs) were assessed for their potential as co-sequestrating agents in carbon capture. Carbonic anhydrase (CA) was added to promote both CO2 hydration and residue mineral dissolution, offering an enhancement in CO2-capture yield under atmospheric (up to 4-fold) and industrial-gas mimic conditions (up to 2.2-fold). Geological CO2 storage using olivine as a reference material was employed in two stages: one involving mineral dissolution, with leaching of Mg2+ and SiO2 from olivine; and the second involving mineral carbonation, converting Mg2+ and bicarbonate to MgCO3 as a permanent storage form of CO2. The results showed an enhanced carbonation yield up to 6.9%, when CA was added in the prior CO2-capture step. The proposed route underlines the importance of the valorization of industrial residues toward achieving neutral, or even negative emissions in the case of bioenergy-based plants, without the need for energy-intensive compression and long-distance transport of the captured CO2. This is a proof of concept for an integrated strategy in which a biocatalyst is applied as a CO2-capture promoter while CO2 storage can be done near industrial sites with adequate geological characteristics.

Analysis of production routes for silicon carbide using air as carbon source empowering negative emissions

A rapid defossilisation of the industry sector is required to stop further greenhouse gas emissions and to curb global warming. Additionally, to avoid irreversible consequences caused by climate change, the deployment of negative emission technologies is required to reduce the carbon dioxide (CO2) concentration in Earth’s atmosphere to a sustainable level. A novel approach to store gaseous CO2 from direct air capture facilities in solid silicon carbide (SiC) is presented. A chain of established processes to produce SiC from renewable electricity and air is evaluated in terms of energy and mass balances. Furthermore, possible fields of SiC utilisation are considered. Electricity-based SiC (e-SiC) can serve the growing global market for technical ceramics and can possibly be used to tackle increasing construction sand shortages in the construction industry by partially substituting sand. Calculations of the levelised cost of carbon dioxide removal show that storing ambient CO2 in solid SiC that can be subsequently sold on the world market can eventually create profit. In 2050, a net benefit of 259 €/tCO2 or 631 €/tSiC can be realised if the SiC product is sold at the world market with additional carbon compensation. Therefore, the proposed SiC production chain might be able to challenge conventionally produced SiC, while empowering negative emissions. In 2050, the net CO2 emission potential is limited to about 290 MtCO2/a for technical ceramics, but may reach up to 13.6 GtCO2/a for construction sand. Results show that e-SiC production is economically feasible for technical ceramics but not for construction sand without further process cost decrease. Alternative processes to produce e-SiC are described and evaluated. Future research opportunities are discussed.

Assessing China's Path to Carbon Neutrality: Analyzing Historical and Projected Electricity-Related Carbon Emissions in the Context of the Dual Carbon Plan

Carbon emissions have become a hot topic in the energy sector. China has proposed the "Dual Carbon Plan," aiming to peak its carbon dioxide emissions by 2030 and achieve carbon neutrality by 2060, whereby carbon emissions will be completely offset or absorbed, resulting in a net zero or negative carbon emission balance. However, China's heavy reliance on coal for electricity generation, coupled with issues of overcapacity and relatively backward technology, not only leads to significant carbon emissions but also poses challenges for a rapid transition to clean energy. This paper analyses historical data on China's total carbon emissions and carbon emissions from electricity generation. Additionally, it predicts future electricity-related carbon emissions based on policy and technological scenarios proposed by existing scholars, discussing the feasibility of achieving the goals set forth in the Dual Carbon Plan.

Effectiveness of Chemical Oxygen Demand as an Indicator of Organic Pollution in Aquatic Environments

The chemical oxygen demand (COD) is an essential indicator of organic pollution that represents the amount of bulk carbon in water. COD is strongly correlated with nutrient cycles and other pollutants in the environment, but it has a limited ability to quantify the amount of organic carbon (OC), of which a large proportion is made up of refractory dissolved organic carbon (RDOC) and is a potential carbon sink. Moreover, the biodegradability of OC in terms of its fate and destination should be explored, as well as how this is reflected by COD. Methods based on particle size, spectroscopy, and isotopic tracing are expected to help with deciphering the bioavailability of COD-responsive OC and explore the processes of biogeochemical cycles. As the pressure on the environment from anthropogenic inputs increases, understanding the bioavailability of OC associated with COD will help with developing more precise scientific indicators for environmental monitoring and identifying how new tools will increase knowledge of the carbon cycle. In this review, we discuss the application, scope, means, and advances of COD measurement. Based on data in the literature, we estimate the global RDOC stock and assess the impact of anthropogenic RDOC on the carbon cycle in offshore bays. This review presents new insights into the behavior of OC in aquatic environments and a potential pathway for ocean negative carbon emissions by expanding the role of RDOC as a carbon sink to offset the effect of anthropogenic carbon emissions.

Carbon-negative hydrogen: aqueous phase reforming (APR) of glycerol over NiPt bimetallic catalyst coupled with CO2 sequestration

Carbon-negative H2 can be produced by coupling APR technology with CO2 sequestration. APR of glycerol over NiPt bimetallic catalyst coupled with CCUS can produce H2 with negative GHG emissions (–57 CO2 eq. per kg H2) using renewable electricity.

Negative Emission Technologies and Climate Cooperation

Negative Emission Technologies and Climate Cooperation

A Canadian case study of carbon dioxide removals and negative emission hydrogen production

A Canadian case study of carbon dioxide removals and negative emission hydrogen production