Biofuels from microalgae: photoconversion efficiency during lipid accumulation.

The accumulation of storage lipids in oleaginous microalgae can be induced by a targeted nutrient limitation. Experiments with varying concentrations of nitrate in the culture medium showed differing volumetric productivities of Phaeodactylum tricornutum in batch experiments. This was partially attributable to the differentiated ability of cultures to absorb light. Apart from that, it was demonstrated that storage molecule accumulation follows kinetics that show saturation at high photon flux densities. The measurement of the photoconversion efficiency (PCE) based on a rigorous balancing of absorbed light energy and changes in the enthalpy of combustion of biomass during nutrient depletion. In batch experiments the PCE was increased more than twofold, from 2.48% at low nitrate concentrations to a maximum value of 5.65%, by increase of the nitrogen availability.