Clean Technologies

Copper is a strategic raw material and an important component in electric motors, widely used across industries because of its excellent conductivity and recyclability. It plays an important role in the transformation from fossil fuel-based systems to green, electrified systems. However, substantial material losses continue throughout the lifecycle of electric motors, even with copper’s intrinsic capacity for circularity. Also, copper’s increasing demand, which is driven by the emergence of electric vehicles, industrial electrification, and renewable energy infrastructure, poses questions regarding its sustainable supply. The recovery of secondary copper sources from end-of-life (EoL) products is becoming more and more important in this context. However, it is still difficult to achieve circularity of copper, especially from industrial electric motors. This study investigates the challenges of closing the loop for copper during the lifecycle of motors in industrial applications. Based on an examination of EoL strategies, material flow insights, and practical investigation, the research pinpoints significant inefficiencies in the current processes. The widespread use of scraping as an approach of end-of-life management is one significant issue. Most of the electric motors are not built to separate their components, which makes both mechanical and manual disassembly difficult. The quality of recovered copper is thus compromised by the dominance of mixed metal shredding methods in the recycling step. This study highlights the need for systemic changes in addition to technical solutions to address copper circularity issues. It requires a focus on circularity in designing, giving disassembly and metal recovery a priority. This study focuses on circularity and its technological challenges in a value chain of copper. It not only identifies different processes such as supply chain disconnections and design constraints, but it also suggests workable solutions to close the copper flow loop in the electric motor sector. Copper quality and recovery is ultimately a problem involving design, technology, and cooperation, in addition to resources. This study supports the transition to a more sustainable and circular electric motor industry by offering a basis for directing such changes in industry practices and prospective EU regulations.

This study evaluated low-cost food waste anaerobic digestion (FWAD) designed for African urban informal settlements, where electricity and process control are limited. Eight small-scale reactors were operated under varying mixing, pH control, and temperature conditions to assess the feasibility of stable operation with minimal input. Results showed no significant difference in methane yield between continuously mixed and minimally mixed (48-hourly) systems, nor between reactors with continuous pH dosing and those adjusted every 48 h (ANOVA p > 0.05 for all comparisons). The highest mean methane yield, 0.267 L CH₄ g VS⁻¹, was achieved by the minimally mixed reactor with 48-hourly pH control at 30 °C, while the controlled reactor at 37 °C produced a comparable 0.247 L CH₄ g VS⁻¹. Total methane production was similar at both temperatures, although gas generation was faster during the first 24 h at 37 °C. Compared to gas recovery achieved by extended batch operation following semi-continuous feeding, 58–73% of total methane was produced within the 48-h cycle, suggesting conversion could increase by 30–40% with extended liquid retention. Microbial analyses showed compositional differences but consistent performance, indicating functional redundancy within the microbial consortia. These results confirm the capacity of FWAD for stable, efficient biogas production without continuous energy input.

The increasing atmospheric concentration of carbon dioxide (CO₂) poses a critical threat to global climate stability, highlighting the need for efficient carbon capture technologies. While amine-based solvents such as monoethanolamine (MEA) are widely used for industrial CO₂ capture, they are subject to limitations such as high energy requirements for regeneration, solvent degradation, and environmental concerns. This study investigates potassium carbonate/bicarbonate system as an alternative solution for CO₂ absorption. The absorption mechanism and reaction kinetics of potassium carbonate in the presence of bicarbonates were reviewed. A rate-based model was developed in Aspen Plus, using literature kinetics, to simulate CO₂ absorption using 20 wt% potassium carbonate (K₂CO₃) solution with 10% carbonate-to-bicarbonate conversion under different industrial conditions. Three flue gas compositions were evaluated: cement industry, biomass combustion, and anaerobic digestion, each at 3000 m³/h flow rate. The simulation was conducted to determine minimum column height and solvent loading requirements with a target output of 90% CO₂ removal from the gas streams. Results demonstrated that potassium carbonate systems successfully achieved the target removal efficiency across all scenarios. Column heights ranged from 18 to 25 m, with molar K₂CO₃/CO₂ ratios between 1.41 and 4.00. The biomass combustion scenario proved most favorable due to lower CO₂ concentration and effective heat integration. While requiring higher column heights (18–25 m) compared to MEA systems (6–12 m) and greater solvent mass flow rates, potassium carbonate demonstrated technical feasibility for CO₂ capture. The findings of this study provide a foundation for technoeconomic evaluation of potassium carbonate systems versus amine-based technologies for industrial carbon capture applications.