Productivity and biochemical composition of Tetradesmus obliquus and Phaeodactylum tricornutum: effects of different cultivation approaches

The present work evaluated biomass productivity, carbon dioxide fixation rate, and biochemical composition of two microalgal species, Phaeodactylum tricornutum (Bacillariophyta) and Tetradesmus obliquus (Chlorophyta), cultivated indoors in high-technology photobioreactors (HT-PBR) and outdoors both in pilot ponds and low-technology photobioreactors in a greenhouse in southern Italy. Microalgae were grown in standard media, under nitrogen starvation, and in two liquid digestates obtained from anaerobic digestion of agro-zootechnical and vegetable biomass. P. tricornutum, cultivated in semi-continuous mode in indoor HT-PBRs with standard medium, showed a biomass productivity of 21.0 ± 2.3 g m−2 d−1. Applying nitrogen starvation, the lipid productivity increased from 2.3 up to 4.5 ± 0.5 g m−2 d−1, with a 24 % decrease of biomass productivity. For T. obliquus, a biomass productivity of 9.1 ± 0.9 g m−2 d−1 in indoor HT-PBR was obtained using standard medium. Applying liquid digestates as fertilizers in open ponds, T. obliquus gave a biomass productivity (10.8 ± 2.0 g m−2 d−1) not statistically different from complete medium such as P. tricornutum (6.5 ± 2.2 g m−2 d−1). The biochemical data showed that the fatty acid composition of the microalgal biomass was affected by the different cultivation conditions for both microalgae. In conclusion, it was found that the microalgal productivity in standard medium was about doubled in HT-PBR compared to open ponds for P. tricornutum and was about 20 % higher for T. obliquus.