A systematic study regarding hydrolysis and ethanol fermentation from microalgal biomass

In this study, acidic and enzymatic hydrolysis were carried out with Chlorella vulgaris and Scenedesmus obliquus, and a systematic evaluation of the yeast inoculum optimization (Saccharomyces cerevisiae and Pichia stipitis) during the hydrolysates fermentation was made. Acidic hydrolysis with 3% of sulphuric acid at 121 °C and 30 min of reaction time (50-100 g/L of biomass) was found as best condition, and more than 90% of sugars recovery in the liquid phase was achieved even though S. obliquus be more sensible to thermal degradation than C. vulgaris. On the other hand, during the enzymatic hydrolysis, ultrasonication showed to be an effective method of biomass pretreatment to provide higher enzyme accessibility what together with a combination between amylases, cellulase/hemicellulase mix and pectinases achieved more than 90% of sugars recovery in 8 h of hydrolysis time. Thus, both treatments could recover efficiently the sugars present in microalgae. After inoculum optimization (concentration and consortium between S. cerevisiae and P. stipitis) and saline influence on yeast performance were evaluated, the fermentation of microalgal hydrolysate exhibited very different profiles in comparison with the control conditions and ethanol biochemical yield changed between 45% and 61%, emphasizing the importance to optimize this last but not less important step of ethanol production.