Primary aluminium industry is one of the largest industries associated with high greenhouse gas emissions. It is reported that in 2022, the aluminium production emitted nearly 270 Mt of direct CO2 in the atmosphere. To achieve the European goals of zero emissions by 2050, a reduction of 4% annually is essential. Τhe industry needs to take a turn towards less impactful production practices, focusing on the valorisation of residues for promoting sustainability. Bauxite residue from alumina production represents a remarkable source of Rare Earth Elements (REEs). This study offers valuable insights into the environmental and economic aspects of processes related to resource Scandium (Sc) extraction and processing in Greece, Romania and Turkey. In this frame, a comparative analysis of the environmental impact of the extraction process of REEs from Bauxite Residues (BR) in the regions mentioned above is presented. The results show that an up to 23% greenhouse gas emissions reduction can be achieved, while the environmental categories of human health risks, aquatic toxicity potential, and terrestrial ecotoxicity potential are improved by applying hydrothermal processes and direct leaching to BR. While the stages of Sc extraction remain consistent, variations in the chemical compositions of BR underscore the influence of local factors. The findings also emphasize the importance of tailoring extraction processes to local conditions and compositions for scandium extraction. These insights can guide industry decisions and contribute to responsible resource management in the future.

Food waste (FW) valorization through resource recovery is central to circular economy strategies that reduce environmental burden while generating sustainable, bio-based chemicals. This work investigated the effect of anaerobic sludge inoculum and the process control parameters of temperature (35 °C and 55 °C), pH value (4–10), and total solids content (2.5%, 5%, 7.5% and 10%) on the recovery of volatile fatty acids (VFAs)—chemicals used in bioplastics and bioenergy production—during acidogenic fermentation of food waste in batch reactors. While FW is well studied for biogas production, its potential for VFA recovery, a strategy that adds economic value to waste streams and supports the circular bioeconomy, remains comparatively underexplored. Mesophilic conditions favored fermentation over thermophilic conditions, and pH was the most influential factor affecting VFA accumulation, although temperature, inoculum presence, and total solids content also had statistically significant, large effects. Basic pH values provided maximum VFA yields from 2% to 25%, roughly double the acidic pH yields, while the highest solids content (10%) minimized VFA production at both temperatures. The highest yield (25%) occurred at T = 35 °C, pH 9, and TS = 5%, without sludge, while the highest yield under thermophilic conditions (T = 55 °C) reached 22.4% at TS = 2.5% and pH 9. By systematically evaluating these parameters together, this study offers a more comprehensive understanding of FW acidogenic fermentation than prior single-parameter works, guiding bioprocess design for sustainable waste management and resource efficiency.