Search Results (90)

The integration of renewable energy with circular economy strategies offers effective pathways to reduce greenhouse gas emissions while enhancing local energy independence. This study analyses three real-world projects implemented in Spain that exemplify this synergy. LIFE Smart Agromobility converts pig manure into biomethane to power farm vehicles, using anaerobic digestion and microalgae-based upgrading systems. Smart Met Value refines biogas from a wastewater treatment plant in Guadalajara to produce high-purity biomethane for the municipal fleet, demonstrating the viability of energy recovery from sewage sludge. The UNDERGY project addresses green hydrogen storage by repurposing a depleted natural gas reservoir, showing geochemical and geomechanical feasibility for seasonal underground hydrogen storage. Each project utilises regionally available resources to produce clean fuels—biomethane or hydrogen—while mitigating methane and CO₂ emissions. Results show significant energy recovery potential: biomethane production can replace a substantial portion of fossil fuel use in rural and urban settings, while hydrogen storage provides a scalable solution for surplus renewable energy. These applied cases demonstrate not only the technical feasibility but also the socio-economic benefits of integrating waste valorisation and energy transition technologies. Together, they represent replicable models for sustainable development and energy resilience across Europe and beyond. Full article

This study examines the establishment of a Hub for Circular Economy and Industrial Symbiosis (HUB-CEIS) centred on a forest biomass waste plant in Fundão, Portugal, presenting an innovative model for rural industrial symbiosis, circular economy governance, and sustainable waste management. Designed as a strategic node within a reverse supply chain, the hub facilitates the conversion of solid waste into renewable energy and high-value co-products, including green hydrogen, tailored for industrial and agricultural applications, with an estimated 120 ktCO₂/year reduction and 60 direct jobs. Aligned with the United Nations (UN) Sustainable Development Goals (SDGs) and the Paris Agreement, this initiative addresses global challenges such as decarbonization, resource efficiency, and the energy transition. Employing a mixed research methodology, this study integrates a comprehensive literature review, in-depth stakeholder interviews, and comparative case study analysis to formulate a governance framework fostering regional partnerships between industry, government, and local communities. The findings highlight Fundão’s potential to become a benchmark for rural industrial symbiosis, offering a replicable model for circularity in non-urban contexts, with a projected investment of USD 60 M. Special emphasis is placed on the green hydrogen value chain, positioning it as a key enabler for regional sustainability. This research underscores the importance of cross-sectoral collaboration in achieving scalable and efficient waste recovery processes. By delivering practical insights and a robust governance structure, the study contributes to the circular economy literature, providing actionable strategies for implementing rural reverse supply chains. Beyond validating waste valorization and renewable energy production, the proposed hub establishes a blueprint for sustainable rural industrial development, promoting long-term industrial symbiosis integration. Full article

The excessive use of fossil fuels could bring about a global environmental crisis. Transitioning from a carbon-based to a hydrogen-based economy is an important way to realize the low-carbon energy transition. The key to this economy transformation lies in the efficient utilization of hydrogen. Hydrogen liquefaction is an efficient technology for the transportation and storage of hydrogen, and the liquid hydrogen produced is also a direct feedstock for many important fields. Large-scale liquefaction of hydrogen has not been commercialized due to its high energy consumption (>10 kWh/kg_LH2) and low efficiency (<30%). However, conceptual designs for hydrogen liquefaction with a low energy consumption (about 6.4 kWh/kg_LH2) and high efficiency (>40%) are frequently reported in the existing literature. Therefore, in this paper, the production process of liquid hydrogen is reviewed from three aspects, which are hydrogen pre-cooling, hydrogen cryo-cooling, and ortho-para hydrogen (OPH) conversion. The focus is to summarize effective and realistic hydrogen liquefaction schemes in the existing studies to provide process guidance for the subsequent practical production of liquid hydrogen. The development of open and closed refrigeration cycles for hydrogen pre-cooling is reviewed following the lead of pre-coolant types. The implementation methods of structural optimization of different hydrogen cryo-cooling cycles are clarified and the performance improvements achieved are compared. Different modes of OPH conversion are presented and their realization in simulation and practical applications is summarized. Finally, subjective recommendations are given regarding the content of the review. Full article

Despite growing international consensus on the urgency of climate action, global CO₂ emissions have continued to rise, exposing a critical implementation gap between environmental ambition and reality. This study explores the readiness and structural capacity of the world’s most CO₂-intensive countries to transition toward a green and hydrogen-based economy. We introduce and apply the Green Economy Index, a composite measure integrating 31 indicators across four core dimensions—political and regulatory efficiency, socio-economic status, infrastructure, and sustainable targets. Using data from 29 countries emitting over 200 Mt of CO₂ in 2022, the analysis combines principal component analysis, Random Forest modeling, and network-based correlation analysis to classify nations into frontrunners, transitional performers, and structural laggers. The results reveal significant disparities in green economy readiness, with high-income countries showing institutional maturity and infrastructural robustness, while middle-income nations remain constrained by fossil fuel dependencies and governance challenges. Importantly, we highlight the growing utility of machine learning and multivariate statistics in capturing complex sustainability interdependencies. The Green Economy Index framework offers a relevant tool to benchmark progress, diagnose barriers, and guide targeted interventions in global decarbonization efforts. Full article

Motivated by the growth of global energy demand and the goal of carbon neutrality, lead-cooled fast reactors, which are core reactor types of fourth-generation nuclear energy systems, have become a global research hotspot due to their advantages of high safety, nuclear fuel breeding capability, and economic efficiency. However, its engineering implementation faces key challenges, such as material compatibility, closed fuel cycles, and irradiation performance of structures. This paper comprehensively reviews the latest progress in the core design of lead-cooled fast reactors in terms of the innovation of nuclear fuel, optimization of coolant, material adaptability, and design of assemblies and core structures. The research findings indicate remarkable innovation trends in the field of lead-cooled fast reactor core design, including optimizing the utilization efficiency of nuclear fuel based on the nitride fuel system and the traveling wave burnup theory, effectively suppressing the corrosion effect of liquid metal through surface modification technology and the development of ceramic matrix composites; replacing the lead-bismuth eutectic system with pure lead coolant to enhance economic efficiency and safety; and significantly enhancing the neutron economy and system integration degree by combining the collaborative design strategy of the open-type assembly structure and control drums. In the future, efforts should be made to overcome the radiation resistance of materials and liquid metal corrosion technology, develop closed fuel cycle systems, and accelerate the commercialization process through international standardization cooperation to provide sustainable clean energy solutions for basic load power supply, high-temperature hydrogen production, ship propulsion, and other fields. Full article

The global plastic crisis, with over 400 million metric tons produced annually and minimal recycling, demands urgent solutions. Photocatalytic plastic photoreforming offers a dual benefit: converting non-recyclable plastics into hydrogen fuel and valuable chemicals using solar energy under mild conditions. This critical review highlights recent advances in photocatalyst design, including semiconductors, MOF-derived materials, and co-catalyst systems, and explores key insights into plastic degradation mechanisms and reactor configurations. Operational factors such as pH, light intensity, and flow dynamics are discussed for their impact on hydrogen yield and product selectivity. Life cycle and techno-economic assessments reveal current challenges in efficiency, scalability, and cost to illuminate the feasibility of implementing the technology at industrial scale. This study suggests that innovations in catalyst engineering, light management, and system integration provide viable paths forward. With its potential to upcycle plastic waste and contribute to low-carbon hydrogen economies, photoreforming represents a promising approach in advancing circular economy goals, especially when coupled with policy support and smart separation strategies. Full article

This study examines the policy and technological dynamics shaping China’s road transport sector’s transition to low-carbon sustainability, focusing on battery electric vehicles (BEVs) and hydrogen fuel cell electric vehicles (HFCEVs). As the world’s second-largest carbon emitter, China faces significant challenges in reducing its fossil fuel dependency in road transport, which accounts for diverse emissions and energy security risks. The present work, using a dual tech multi-level perspective (DTMLP) framework integrating multi-level perspective (MLP) and an advocacy coalition framework (ACF), analyzes the interplay of landscape pressures (global carbon constraints), regime dynamics (policy–market interactions), and niche innovations (BEV/FCEV competition). The results reveal BEVs’ dominance in light-duty markets, achieving remarkable operational emission reductions but facing lifecycle carbon lock-ins from battery production and coal-dependent power grids. HFCEVs demonstrate potential for heavy-duty decarbonization but struggle with gray hydrogen reliance and infrastructure gaps. Policy evolution highlights shifting governance from subsidies to market-driven mechanisms, alongside regional disparities in implementation. This study proposes a three-phase roadmap: structural optimization (2025–2030), technological adaptation (2030–2045), and hydrogen–electric system integration (post-2045), emphasizing material innovation, renewable energy alignment, and multi-level governance. Our findings underscore the necessity of coordinated policy–technology synergies, grid decarbonization, and circular economy strategies, to overcome institutional inertia and achieve China’s ‘Dual Carbon’ targets. This work provides actionable insights for global sustainable transport transitions amid competing technological pathways and geopolitical resource constraints. Full article

The coupling of renewable energy sources with electrolyzers under stand-alone conditions significantly enhances the operational efficiency and improves the cost-effectiveness of electrolyzers as a technologically viable and sustainable solution for green hydrogen production. To address the configuration optimization challenge in hybrid electrolyzer systems integrating alkaline water electrolysis (AWE) and proton exchange membrane electrolysis (PEME), this study proposes an innovative methodology leveraging the morphological analysis of Pareto frontiers to determine the optimal solutions under multi-objective functions including the hydrogen production cost and efficiency. Then, the complementary advantages of AWE and PEME are explored. The proposed methodology demonstrated significant performance improvements compared with the single-objective optimization function. When contrasted with the economic optimization function, the hybrid system achieved a 1.00% reduction in hydrogen production costs while enhancing the utilization efficiency by 21.71%. Conversely, relative to the efficiency-focused optimization function, the proposed method maintained a marginal 5.22% reduction in utilization efficiency while achieving a 6.46% improvement in economic performance. These comparative results empirically validate that the proposed hybrid electrolyzer configuration, through the implementation of the novel optimization framework, successfully establishes an optimal balance between the economy and efficiency of hydrogen production. Additionally, a discussion on the key factors affecting the rated power and mixing ratio of the hybrid electrolyzer in this research topic is provided. Full article

Around 75% of worldwide greenhouse gas (GHG) emissions are generated by the combustion of fossil fuels (FFs) for energy production. Tackling climate change requires a global shift away from FF reliance and the decarbonization of energy systems. The energy, manufacturing, and construction sectors contribute a significant portion of Egypt’s total GHG emissions, largely due to the reliance on fossil fuels in energy-intensive industries (EIIs). Decarbonizing these sectors is essential to achieve Egypt’s sustainable development goals, improve air quality, and create a resilient, low-carbon economy. This paper examines practical, scalable solutions to decarbonize energy-intensive industries in Egypt, focusing on implementing renewable energy sources (RESs), enhancing energy efficiency, and integrating new technologies such as carbon capture, utilization, and storage (CCUS) and green hydrogen (GH). We also explore the policy incentives and economic drivers that can facilitate these changes, as the government aims to achieve net-zero GHG emissions for a sustainable transition by 2050. Full article

Hydrogen-Integrated energy systems (HIESs) are pivotal in driving the transition to a low-carbon energy structure in China. This paper proposes a low-carbon economic scheduling strategy to improve the operational efficiency and reduce the carbon emissions of HIESs. The approach begins with the implementation of a stepwise carbon trading framework to limit the carbon output of the system. This is followed by the development of a joint operational model that combines hydrogen energy use and carbon capture. To improve the energy supply flexibility of HIESs, modifications to the conventional combined heat and power (CHP) unit are made by incorporating a waste heat boiler and an organic Rankine cycle. This results in a flexible CHP response model capable of adjusting both electricity and heat outputs. Furthermore, a comprehensive demand response model is designed to optimize the flexible capacities of electric and thermal loads, thereby enhancing demand-side responsiveness. The integration of electric vehicles (EVs) into the system is analyzed with respect to their energy consumption patterns and dispatch capabilities, which improves their potential for flexible scheduling and enables an optimized synergy between the demand-side flexibility and system operations. Finally, a low-carbon economic scheduling model for the HIES is developed with the objective of minimizing system costs. The results show that the proposed scheduling method effectively enhances the economy, low-carbon performance, and flexibility of HIES operation while promoting clean energy consumption, deep decarbonization of the system, and the synergistic complementarity of flexible supply–demand resources. In the broader context of expanding clean energy and growing EV adoption, this study demonstrates the potential of energy-saving, emission-reduction systems and vehicle-to-grid (V2G) strategies to contribute to the sustainable and green development of the energy sector. Full article

Red mud (RM), the primary waste product of the aluminium industry, is notable for its high concentrations of metals and rare earth elements (REE). Efforts have been made to develop extraction methods for REE recovery from RM, aiming to enhance its valorisation and reduce the European reliance on external REE sources—particularly crucial for technological advancements and the transition to renewable energy. However, these methods have only been limited to low technology readiness levels (TRLs), with no economically or technically viable processing routes yet defined to enable large-scale industrialisation within a circular economy model. This study characterised RM samples from the Seydişehir region in Türkiye using different techniques and explored the experimental process for recovering metals and REE. Moreover, the study assessed the global prospective potential of RM based on technical and economic data, as well as the sustainability of the implemented process through the life cycle assessment (LCA) tool. Results showed a total REE concentration of up to 1600 ppm, with Ce, being the most abundant (426 ± 27 ppm), followed by La, Nd, and Sc. Concentration efficiencies for La and Nd ranged between 240–300%. Sc, Y, Ce, La, and Nd have significant usage in European markets and represent prime RM targets for further prospecting. The LCA revealed that the highest global warming potential of the sequential extraction process was attributed to hydroxylamine hydrochloride and hydrogen peroxide. The findings highlight the need to explore alternative, more eco-friendly reagents to improve RM valorisation. Full article

The modern construction of transmission networks for transporting energy resources (e.g., crude oil, gas, hydrogen) or electricity is increasingly being carried out using trenchless technologies. Trenchless methods significantly reduce the need for extensive earthworks; however, they consequently generate substantial amounts of drilling waste. This waste consists primarily of a mixture of spent drilling fluids and drill cuttings. Due to the volume and composition of the waste, along with the rapidly increasing costs of waste disposal, the trenchless technology industry faces significant economic and environmental challenges related to circular economy principles in waste management. This article presents an analysis of trenchless construction methods for underground transmission networks, with particular emphasis on the quantity and quality of the generated drilling waste. Furthermore, research is conducted to develop a cationic flocculant based on polyvinylamine, designed to eliminate the harmful coagulants in drilling waste treatment technology. Based on the conducted studies, we propose a closed-loop waste management system for trenchless technologies. The implementation of circular economy principles, along with the integration of drilling fluid treatment systems with photovoltaic panels and energy storage units, enhances the energy efficiency of drilling waste treatment processes and aligns with global trends in the adoption of renewable energy sources (RESs). Full article

Biorefineries play a critical role in addressing current global sustainability challenges by converting renewable biomass into valuable products such as biofuels, biochemicals, and bioenergy. The necessity of biorefineries has increased due to the growing demand for eco-friendly alternatives to fossil fuels, mitigating climate change, and reducing environmental impact. Utilizing agricultural byproducts, forest residues, and municipal waste, biorefineries harness feedstock through techniques such as pretreatment, anaerobic digestion, and thermochemical transformation, alongside advanced methods including electrochemical processes, hydrogenation of bio-derived substances, and the implementation of complex biocatalysts within biomass-oriented biorefineries. These processes enhance the efficiency of bioenergy production by breaking down complex biomass into simpler components. The current capacity of biorefineries is expanding globally, with increasing interest in advanced technologies such as gasification, fermentation, and enzymatic conversion. While biorefineries offer significant potential for reducing waste and promoting a circular economy, challenges such as scalability and cost efficiency remain. Future trends include integrating new biotechnological advances and optimizing resource recovery systems to improve yield, profitability, and sustainability in the bioeconomy. Full article

Global warming caused by greenhouse gas emissions has become a worldwide environmental problem, posing a great threat to human survival. As the world’s largest emitter of carbon dioxide, China has pledged to reach peak carbon emissions by no later than 2030 and carbon neutrality by 2060. It is found that a carbon tax is a powerful incentive to reduce carbon emissions and promote an energy revolution, but it may have negative socio-economic impacts. Therefore, based on China’s 2020 input–output table, this paper systematically investigates the impacts of a carbon tax on China’s economy, carbon emissions, and energy by applying a computable general equilibrium model to determine the ideal equilibrium between socio-economic and environmental objectives. Based on energy use characteristics, we subdivided the energy sector into five major sectors: coal, oil, natural gas, thermal power generation, and clean power. The results show that when the carbon emission reduction target is less than 15%, that is, when the equilibrium carbon tax price is less than 54 yuan/ton, the implementation of a carbon tax policy can significantly reduce carbon emission and fossil fuel energy consumption, while only slightly reducing economic growth rate, and can achieve the double dividend of environment and economy. Moreover, because the reduction of coal consumption has the greatest impact on reducing carbon emissions, the ad valorem tax rate on coal after the carbon tax is imposed is the highest because coal has the highest carbon emission coefficient among fossil fuels. In addition, as an emerging clean energy source, hydrogen energy is the ideal energy storage medium for achieving clean power generation in power systems. If hydrogen energy can be vigorously developed, it is expected to greatly accelerate the deep decarbonization of power, industry, transportation, construction, and other fields. Full article

Rare-earth-metal-based materials have emerged as frontrunners in the quest for high-performance hydrogen storage solutions, offering a paradigm shift in clean energy technologies. This comprehensive review delves into the cutting-edge advancements, challenges, and future prospects of these materials, providing a roadmap for their development and implementation. By elucidating the fundamental principles, synthesis methods, characterization techniques, and performance enhancement strategies, we unveil the immense potential of rare-earth metals in revolutionizing hydrogen storage. The unique electronic structure and hydrogen affinity of these elements enable diverse storage mechanisms, including chemisorption, physisorption, and hydride formation. Through rational design, nanostructuring, surface modification, and catalytic doping, the hydrogen storage capacity, kinetics, and thermodynamics of rare-earth-metal-based materials can be significantly enhanced. However, challenges such as cost, scalability, and long-term stability need to be addressed for their widespread adoption. This review not only presents a critical analysis of the state-of-the-art but also highlights the opportunities for multidisciplinary research and innovation. By harnessing the synergies between materials science, nanotechnology, and computational modeling, rare-earth-metal-based hydrogen storage materials are poised to accelerate the transition towards a sustainable hydrogen economy, ushering in a new era of clean energy solutions. Full article