Lipid productivity in the fed-batch growth of Desmodesmus green microalgae from sugarcane vinasse

Abstract. The technological potential of biodiesel from microalgae depends on the growth characteristics and lipid accumulation of these microorganisms. In this sense, the use of wastewater becomes an alternative biomass production as compared to traditional methods of photoautotrophic culture. The use of microalgae in the wastewater treatment has been studied as an alternative to conventional decontamination processes. Green microalgae Desmodesmus subspicatus has shown high cell viability in effluents, tolerating changes in temperature and pH. Vinasse is the main wastewater from sugarcane processing generated by ethanol fermentation-distillation, which presents high organic matter (non-volatile molecules with high molecular weight) and salts. Several strategies have been propose to improve the accumulation of lipids in the microalgal biomass, such as nutrient limitation and temperature. As the accumulation of intracellular lipids is dependent on biomass accumulation, fed-batch strategies can become attractive. In this sense, the study aimed to evaluated lipid productivity in the fed-batch growth of green microalgae Desmodesmus subspicatus from sugarcane vinasse. The experiments were set up a heterotrophic stirred bioreactor with 3 L of sugarcane vinasse, aeration of 1 VVM (volume of air per volume of liquid per minute) and 25°C. Lipid extraction using CO₂-SC was conducted in a semi-continuous supercritical fluid extraction apparatus. Results of fed-batch cultivation indicate duplication biomass during fed-batch time (9 hours), with lipid content in the biomass around 15%. Thus, it was lipid productivity of 360 mg L^-1day^-1, similar value of simple batch experiments of our research group, suggesting the technical feasibility of fed-batch microalgae growth from this wastewater.