Nannochloropsis sp. F&M-M24: oil oroduction, effect of mixing on productivity and growth in an industrial wastewater

The energy balance of microalgal biodiesel production is rarely considered. Besides, the actual potential of microalgae as triglyceride producers is often overestimated. This work was aimed at investigating these critical aspects using the marine eustigmatophyte Nannochloropsis sp. F&M-M24, a promising oil producing strain, as model organism and the ''Green Wall Panel'' as culture system. First, the influence of air-flow rate on volumetric productivity of the microalga was evaluated. At low and medium irradiances, no significant differences in productivity occurred at the three different mixing rates tested, while at high irradiances an increase in the air-flow rate resulted in significantly higher volumetric productivities. These results allow to foresee a strategy of airflow rate tuning in accordance to radiation, that may lead to substantial energy savings and, consequently, to more favorable energy and economic balances in the cultivation process. Second, the lipid content and fraction distribution of the biomasses produced under nutrient sufficient and nitrogen-starved conditions were analyzed and the neutral lipid fraction was fully characterized. Finally, the alga was grown in bubbled-tubes using a culture medium prepared with an industrial wastewater, to evaluate its ability to use a free of charge source of nutrients, the exploitation of which may improve biomass production economics.