An unconventional two-stage cultivation strategy to increase the lipid content and enhance the fatty acid profile on Chlorella minutissima biomass cultivated in a novel internal light integrated photobioreactor aiming at biodiesel production

Biodiesel quality is dependent upon the fatty acids distribution of the raw material used in the trans/esterification reactions. While microalgae cells are regarded as potential oil suppliers for the biodiesel production chain, a common criticism is related to the low lipid productivities and often to a poor fatty acid distribution. In the present work we propose to submit microalgal cultivation to a second stage with nutritional stress by a simple addition of a 70% nitrate source depleted medium at the beginning of stationary phase, without harvesting cells, saving time and water. Chlorella minutissima was cultivated in a novel unconventional photobioreactor, named Internally Illuminated Integrated Photobioreactor (ILIPBR), to verify the efficiency of the proposed strategy. Biomass concentration, lipid content and volumetric lipids productivity increased 24.9%, 120.7% and 55.6%, respectively, from Stage 1 to Stage 2, when ILI-PBR was illuminated by constant blue LED and 0.5 vvm of aeration. The fatty acid profiles, evaluated in terms of LED illumination (white, red and blue), showed a predominance of palmitic acid in all cases (59.49%, 57.28% and 46.51%, respectively), which allowed to enhance some biodiesel properties such as cetane number, cold filter plugging point, density and kinematic viscosity, according to international specifications. (C) 2020 Elsevier Ltd. All rights reserved.