Phaeodactylum tricornutum cultivation under mixotrophic conditions with glycerol supplied with ultrafiltered digestate: A simple biorefinery approach recovering C and N.

Abstract Phaeodactylum tricornutum was cultivated mixotrophically in batch mode providing glycerol as the C source, i.e., 0.02, 0.03 and 0.04 Mol L−1 glycerol, and ultrafiltered digestate (UF) as an N source. Biomass productivity, biomass composition, N efficiency use and total energy balance were recorded and compared to those under autotrophic conditions. Under mixotrophic conditions (0.03 Mol L-1 and 0.04 Mol L-1 glycerol), biomass productivity of P. tricornutum increased by 1.29 and 1.60 times in comparison with autotrophic conditions. Algal protein content declined as glycerol concentration increased, contrary to the case of the carbohydrate content. Lipid content did not change but unexpectedly, a lower unsaturated fatty acid in mixotrophic culture was observed than that from autotrophic culture. Mixotrophic conditions offered a higher energy recovery efficiency (EFt) than autotrophic conditions (5.7 % in 0.04 Mol L−1 glycerol and 4.2 % in autotrophic trial, respectively). Additionally, the efficiency of glycerol conversion into biomass (EFgly) increased with the glycerol dose, achieving 22.8 % for 0.04 Mol L−1 glycerol.