Dual-mode cultivation of Chlorella protothecoides applying inter-reactors gas transfer improves microalgae biodiesel production

• Setup of fermenter connected to photobioreactor improves microalga productivity.
• Enhancement of microalga growth by CO2 from off-gases fermentation.
• Efficient CO2 fixation by autotrophic Chlorella protothecoides.
• Lutein and lipids source to produce high value product and biodiesel, respectively.
• Bioreactors association is a feasible way to restore O2 spent in fermentation.

Chlorella protothecoides, a lipid-producing microalga, was grown heterotrophically and autotrophically in separate reactors, the off-gases exiting the former being used to aerate the latter.Autotrophic biomass productivity with the two-reactor association, 0.0249 g L−1 h−1, was 2.2-fold the value obtained in a control autotrophic culture, aerated with ambient air. Fatty acid productivity was 1.7-fold the control value.C. protothecoides heterotrophic biomass productivity was 0.229 g L−1 h−1. This biomass’ fatty acid content was 34.5% (w/w) with a profile suitable for biodiesel production, according to European Standards.The carbon dioxide fixed by the autotrophic biomass was 45 mg CO2 L−1 h−1 in the symbiotic arrangement, 2.1 times the control reactor value.The avoided CO2 atmospheric emission represented 30% of the CO2 produced in the heterotrophic stage, while the released O2 represented 49% of the oxygen demand in that stage.Thus, an increased efficiency in the glucose carbon source use and a higher environmental sustainability were achieved in microalgal biodiesel production using the proposed assembly.