The transition to sustainable energy systems has intensified the search for renewable alternatives to reduce greenhouse gas emissions and reliance on fossil fuels. In this context, microalgae have emerged as a promising third-generation feedstock for biofuel production due to their rapid development, high lipid content, and ability to grow in wastewater without competing with freshwater resources. In this study, the hydrotreatment of biocrudes derived from C. vulgaris, T. obliquus, and a mixed microalgal culture cultivated in domestic wastewater is investigated. Catalytic upgrading was applied using sulphided CoMo/Al₂O₃ (sCoMo) and Pt/Al₂O₃ catalysts. The results demonstrated that catalytic upgrading enhanced the upgraded bio-oils’ quality compared to non-catalysed reactions, confirming the crucial role of catalysts in improving bio-oil properties. Compared with the Pt catalyst, sCoMo produced higher yields of upgraded bio-oil, greater enrichment in carbon and hydrogen, and higher heating value (HHV), while effectively enhancing nitrogen and oxygen removal. However, when compared with the non-sulphided CoMo, the sulphiding treatment did not significantly improve denitrogenation and treated oil yields. The highest fraction of components within the jet fuel boiling range (37.7%) was obtained using a Pt catalyst, while the non-catalysed process yielded the lowest (26.6%). In this sense, catalytic upgrading of microalgae-based biocrude represents an important step towards the production of advanced and environmentally sustainable fuels.

Winery wastewater (WWW), if released untreated, poses a serious environmental threat due to its high organic load. In this study, Chlorella vulgaris was cultivated in diluted WWW to assess its suitability as a culture medium. Two outdoor cultivation systems—a 270 L raceway and a 40 L bubble column—were operated over 33 days using synthetic medium (control) and WWW. A flow cytometry (FC) protocol was implemented to monitor key physiological parameters in near-real time, including cell concentration, membrane integrity, chlorophyll content, cell size, and internal complexity. At the end of cultivation, the bubble column yielded the highest cell concentrations: 2.85 × 10⁶ cells/mL (control) and 2.30 × 10⁶ cells/mL (WWW), though with lower proportions of intact cells (25% and 31%, respectively). Raceway cultures showed lower cell concentrations: 1.64 × 10⁶ (control) and 1.54 × 10⁶ cells/mL (WWW), but higher membrane integrity (76% and 36% for control and WWW cultures, respectively). On average, cells grown in the bubble column had a 22% larger radius than those in the raceway, favouring sedimentation. Heterotrophic cells were more abundant in WWW cultures, due to the presence of organic carbon, indicating its potential for use as animal feed. This study demonstrates that FC is a powerful, real-time tool for monitoring microalgae physiology and optimising cultivation in complex effluents like WWW.

The cork industry generates valuable by-products and residues with significant potential within a circular bioeconomy framework. This study evaluated the energy-driven valorization of two post-consumer cork residues—natural cork stoppers (NCS) and technical cork stoppers (TCS)—through anaerobic digestion and pyrolysis. Both NCS and TCS exhibited low moisture and ash content, a high heating value of 25.14 and 29.88 MJ/kg, respectively, a carbon content exceeding 58 wt% and low nitrogen, sulfur and chlorine concentrations. These characteristics highlight the suitability of NCS and TCS for energy recovery applications. Anaerobic digestion produced biogas containing 68.5 vol% of methane after alkaline pretreatment of TCS. However, the maximum biochemical methane potential was low, reaching only 19.5 L CH₄/kg VS. The resulting digestates contained nitrogen, phosphorus and potassium at levels compatible with agricultural use. Slow pyrolysis of the cork residues resulted in high biochar yields, with NCS achieving an average yield of 64.8 wt%. Combined with carbon contents of up to 66.3 wt%, the biochars produced from NCS and TCS show strong potential for valorization as solid energy carriers, as well as for applications such as activated carbon production and soil amendment. Overall, thermochemical conversion via pyrolysis proved to be the most effective pathway for energy valorization of the tested cork residues, whereas the performance of anaerobic digestion remained limited unless more intensive pretreatment strategies were applied.