Engineering strategies for the enhancement of Nannochloropsis gaditana outdoor production: Influence of the CO2 flow rate on the culture performance in tubular photobioreactors

The aim of this study was to evaluate the influence of the CO2-specific flow rate on pH control, CO2 use efficiency and biomass and lipid productivity of Nannochloropsis gaditana cultivated in outdoor tubular photobioreactors of 3.0 m(3). In that study was evaluated the injection of CO2-specific flow rates ranging from 0.4 to 7.7 mL(co2) L-culture(-1) min(-1). The use of low CO2-specific flow rates, from 0.4 to 1.9 mL(co2) L-cuiture(-1) min(-1), has enabled pH control. The highest biomass productivities and CO2 use efficiency were obtained using the flow rates of 1.2 and 1.9 mL(co2) L-culture(-1) min(-1). The highest lipid productivities were verified in experiments with flow rates of 0.4 mL(co2) L-cuiture(-1) min(-1), followed by 1.9 mL(co2) L-cuiture(-1) min(-1). A high CO2-specific flow rate increases CO2 loss and reduces the performance of the cells due to inadequate pH control. By contrast, a low CO2-specific flow rate prevents adequate pH control and the performance of the cultures. Considering the results provided, an optimal CO2-specific flow rate (1.9 mL(co2) L-culture(-1) min(-1)) was obtained for outdoor photobioreactor operations to produce N. gaditana, thus contributing to cost reduction.