Browsing by Author "Oliveira, Sandra"
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- Lipid Content and Productivity of Arthrospira platensis and Chlorella vulgaris under Mixotrophic Conditions and Salinity StressPublication . Mata, Teresa M.; Martins, António A.; Oliveira, Octávio; Oliveira, Sandra; Mendes, Adélio M.; Caetano, Nídia SáThis study aims at evaluating the influence of mixotrophic growth and salinity stress in the lipid content and productivities of microalgae Arthrospira platensis (A. platensis) and Chlorella vulgaris (C. vulgaris). For comparison purposes, both microalgae were also cultivated in the standard autotrophic conditions: modified Zarrouk’s medium for A. platensis and Bold’s basal medium for C. vulgaris. The mixotrophic conditions were created by adding 1.00 g/L of glucose to their standard media, and the salt stress was induced by introducing sodium chloride (NaCl) in different amounts. As expected, the biomass concentration and productivity increases under mixotrophy but decreases with salinity stress. Therefore, although the lipid content increased with the salinity stress under mixotrophy, reaching maximum values of 15.4 and 23.0 % dry weight (dwt) respectively, for A. platensis (in 0.428 M of NaCl) and C. vulgaris (in 0.0214 M of NaCl), the biomass productivity reached minimum values. Consequently, the maximum biomass and lipid productivities were obtained with an intermedium lipid content and without the salinity stress. The maximum biomass and lipid productivities are 99.7 and 9.7 mg/L/day for A. platensis and 227.2, and 37.7 mg/L/day for C. vulgaris, respectively. This study also revealed that C. vulgaris adapts faster to salinity stress, whereas A. platensis is able to tolerate higher salinity concentrations.
- Sustainability Evaluation of Biodiesel from Arthrospira platensis and Chlorella vulgaris under Mixotrophic Conditions and Salinity StressPublication . Martins, António A.; Mata, Teresa M.; Oliveira, Octávio; Oliveira, Sandra; Mendes, Adélio M.; Caetano, Nídia SáThis study performs a sustainability evaluation of biodiesel production from microalgae Arthrospira platensis (A. platensis) and Chlorella vulgaris (C. vulgaris) cultivated in mixotrophic conditions, with and without salinity stress, in comparison to autotrophic conditions. The life cycle steps considered for the evaluation are microalgae cultivation, biomass harvesting, lipids extraction, biodiesel production, distribution and use. Three sustainability indicators (LCEE – Life Cycle Energy Efficiency, FER – Fossil Energy Ratio and GW – Global Warming) are calculated based on laboratory experiments conducted in this study and literature data to complement inventory data, thus allowing a more truthful and accurate sustainability evaluation. Results show that in the current conditions, production of biodiesel from these microalgae is not energy efficient, since LCEE and FER values are lower than one, except for C. Vulgaris at mixotrophic growth, without salinity stress. GW values are always positive, meaning that carbon captured during microalgae growth does not compensate the carbon emitted in the whole process. A comparative analysis of the various process steps is also conducted, showing that the water removal and lipids recovery are critical steps for the process sustainability. One possible solution is to explore these microalgae in a biorefinery process, where the desired product is obtained along with a host of by-products, increasing the process sustainability and competitiveness.