ISEP - DM – Energias Sustentáveis
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Browsing ISEP - DM – Energias Sustentáveis by Subject "Açúcares fermentáveis"
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- Produção de bioetanol a partir de biomassa microalgal utilizada no tratamento de águas residuaisPublication . COSTA, SÓNIA SOFIA LOBÃO DA; Caetano, Nidia de SáWastewater treatment is a major environmental challenge, while microalgae offer a sustainable solution by simultaneously removing nutrients and generating biomass suitable for bioenergy production. This study examines the integration of microalgae in wastewater treatment, as well as the valorization of the resulting biomass for bioethanol production. Cultivation experiments were conducted using effluents from the Gaia Litoral wastewater treatment plant, employing a 50:50 (v/v) mixture of primary-treated and secondary-treated wastewater, scaled up to a final volume of 30 liters over four weeks. Physicochemical and biological parameters were monitored, revealing high nutrient removal efficiencies: up to 97% for inorganic carbon, 83% for total nitrogen, and 82% for orthophosphate. Microscopic analysis confirmed the predominance of Scenedesmus sp. within the microalgal consortium. Episodes of sedimentation and acidification were mitigated by periodic medium renewal, thereby ensuring the stability of the cultures throughout the study. Regarding biomass valorization, twelve different combinations of pretreatment and hydrolysis were evaluated. Although glucose release was limited, the samples subjected to thermal pretreatment or ultrasound-assisted pretreatment followed by enzymatic hydrolysis with Ultraflo exhibited the highest sugar concentrations, with Samples 6 and 11 standing out, showing arabinose concentrations of 2.962 g/L and 0.654 g/L, respectively, after hydrolysis, and corresponding biomass concentrations of 1.105 g/L and 2.370 g/L. After fermentation, arabinose decreased to 0.211 g/L and 0.008 g/L in the same samples, indicating partial fermentation. Fermentation using Saccharomyces cerevisiae resulted in low ethanol yields (<0.056% v/v), with the highest absolute yield obtained in Sample 10 (0.220 g in 500 mL), restricted by incomplete hydrolysis, possible inhibitor formation such as phenolics, organic acids, and salt residues, and limited pentose fermentation by Saccharomyces cerevisiae (that could be improved by using a yeast able to ferment pentoses, such as Pichia stipitis). Despite these limitations, the results demonstrate the potential of microalgae in integrated processes of environmental remediation and energy biomass production, highlighting their contribution to sustainable biorefinery strategies.