Elena Barbera

Cultivation of Scenedesmus obliquus in liquid hydrolysate from flash hydrolysis for nutrient recycling

The production of biofuels from microalgae is associated with high demands of nutrients (nitrogen and phosphorus) required for growth. Recycling nutrients from the residual biomass is essential to obtain a sustainable production. In this work, the aqueous phase obtained from flash hydrolysis of Scenedesmus sp. was used as cultivation medium for a microalga of the same genus, to assess the feasibility of this technique for nutrient recycling purposes. Batch and continuous cultivations were carried out, to determine growth performances in this substrate compared to standard media, and verify if a stable biomass production could be obtained. In continuous experiments, the effect of hydrolysate inlet concentration and of residence time were assessed to optimize nutrient supply in relation to productivity. Results obtained show that nutrient recycling is feasible by treating biomass with flash hydrolysis, and Scenedesmus is capable of recycling large amounts of recovered nutrients.

Biorefinery as a Promising Approach to Promote Ethanol Industry From Microalgae and Cyanobacteria

Abstract The development of new technologies to increase the production of biofuels without directly competing with food production is a must. Microalgal biomass has recently been highlighted in this regard. In this chapter, the role of this biomass for bioethanol production is discussed within a biorefinery approach, in the view to promote industrial sustainability. Cultivation aimed at accumulating around 50%–60% of carbohydrates in the biomass (dry weight) and the importance of water and nutrient recycling are reviewed. Saccharification of biomass using enzymes or acids is addressed together with alternative operations (such as hydrothermal liquefaction and flash hydrolysis) that aim at recovering additional products (i.e., biocrude). Because the main monosaccharide in microalgal biomass is glucose, high rates of hydrolysis and fermentation are possible, achieving more than 80% of the efficiency as a sum of these two operations. Anaerobic digestion to treat vinasse after distillation and the recycling of CO2 from the ethanolic fermentation and from biogas combustion could increase the process sustainability. Finally, the advantage of using microalgae rather than other sources of biomass in bioethanol production is estimated with reference to the production rate, even though the cultivation costs remain still high.