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- Nitrogen Sources Screening for Ethanol Production Using Carob Industrial WastesPublication . Raposo, Sara; Constantino, Ana; Rodrigues, F.; Rodrigues, Brígida; Lima-Costa, Maria EmíliaNowadays, bioethanol production is one of the most important technologies by the necessity to identify alternative energy resources, principally when based on inexpensive renewable resources. However, the costs of 2nd-generation bioethanol production using current biotechnologies are still high compared to fossil fuels. The feasibility of bioethanol production, by obtaining high yields and concentrations of ethanol, using low-cost medium, is the primary goal, leading the research done today. Batch Saccharomyces cerevisiae fermentation of high-density sugar from carob residues with different organic (yeast extract, peptone, urea) and inorganic nitrogen sources (ammonium sulfate, ammonium nitrate) was performed for evaluating a cost-effective ethanol production, with high ethanol yield and productivity. In STR batch fermentation, urea has proved to be a very promising nitrogen source in large-scale production of bioethanol, reaching an ethanol yield of 44 % (w/w), close to theoretical maximum yield value and an ethanol production of 115 g/l. Urea at 3 g/l as nitrogen source could be an economical alternative with a great advantage in the sustainability of ethanol production from carbohydrates extracted from carob. Simulation studies, with experimental data using SuperPro Design software, have shown that the bioethanol production biorefinery from carob wastes could be a very promising way to the valorization of an endogenous resource, with a competitive cost.
- Kinetic and energetic parameters of carob wastes fermentation by Saccharomyces cerevisiae: crabtree effect, ethanol toxicity, and invertase repressionPublication . Rodrigues, Brígida; Peinado, J. M.; Raposo, Sara; Constantino, Ana; Quintas, Célia; Emília Lima-Costa, MariaCarob waste is a useful raw material for the second-generation ethanol because 50% of its dry weight is sucrose, glucose, and fructose. To optimize the process, we have studied the influence of the initial concentration of sugars on the fermentation performance of Saccharomyces cerevisiae. With initial sugar concentrations (S0) of 20 g/l, the yeasts were derepressed and the ethanol produced during the exponential phase was consumed in a diauxic phase. The rate of ethanol consumption decreased with increasing S0 and disappeared at 250 g/l when the Crabtree effect was complete and almost all the sugar consumed was transformed into ethanol with a yield factor of 0.42 g/g. Sucrose hydrolysis was delayed at high S0 because of glucose repression of invertase synthesis, which was triggered at concentrations above 40 g/l. At S0 higher than 250 g/l, even when glucose had been exhausted, sucrose was hydrolyzed very slowly, probably due to an inhibition at this low water activity. Although with lower metabolic rates and longer times of fermentation, 250 g/l is considered the optimal initial concentration because it avoids the diauxic consumption of ethanol and maintains enough invertase activity to consume all the sucrose, and also avoids the inhibitions due to lower water activities at higher S0.
- Microalgae growth in different trophic conditionsPublication . Constantino, Ana; Jardim, Beatriz; Leon, Antonio; Leon, Rosa; Rodrigues, Brígida; Raposo, SaraMicroalgae growth in different trophic conditions ( Poster Presentation) in Abstract Book 5th Algaeurope Conference
- Biofuels production by chlorella sorokiniana in a biorefinery perspectivePublication . Constantino, Ana; Glória, Patrícia; Rodrigues, Brígida; Leon, Rosa; Barros, Raúl; Raposo, SaraBiofuels Production By Chlorella Sorokiniana In A Biorefinery Perspective (Poster Presentation) in Abstract Book 5th Algaeurope Conference