Bioenergetic potential of Phormidium autumnale´s growth in sugarcane vinasse: feasibility of biodigestion and microalgal biodiesel

Abstract

Microalgal oils, also known as "single-cell lipids" from microalgae, become an environmentally interesting option for biodiesel production. Compared to vegetable oils, single-cell lipids have the advantages of high growth rate, less effect of seasonality and climate, use of different carbon sources via heterotrophic or mixotrophic microalgae growth, in addition to greater ease of scaling. Several studies indicate the possibility of obtaining biodiesel of adequate quality from these microalgal lipids, sometimes from exogenous organic carbon sources, combining the production of biofuel with the use of agro-industrial by-products. Vinasse is the main wastewater in the sugarcane processing, being generated by the distillation step of the alcoholic solution from fermentation in the proportion of approximately 10 liters for each liter of ethanol produced. As the cultivation of microalgae in vinasse by free or immobilized cells does not cause the depletion of the carbon and nutrient sources of this wastewater, the biodigestion of the fraction of biomass not usable for biodiesel and remaining vinasse would close a cycle of harnessing the energy potential of these resources. In this context, the present proposal aims to evaluate the growth of the microalgae Phormidium autumnale free and immobilized using vinasse as a culture medium; to set up a bench bioreactor under selected conditions, with evaluation of the separation and characterization of the biomass in terms of proteins, carbohydrates, lipids, fatty acids, estimation of biodiesel properties and study of the biodigestion of the remaining by-products from microalgal cultivation. (AU)