Microalgae cultivation for biofuel production: optimization of environmental conditions for the intensive culture of Neochloris oleoabundans (Chlorophyta)

Microalgae have the potential to produce environmental friendly biofuels, in view of the growing need for alternatives to fossil resource exploitation. Indeed microalgae grown under nitrogen stress may accumulate significant amount of lipids, which are the raw material for biodiesel. The aim of this study was to optimize culture conditions to increase lipid production on the freshwater green alga Neochloris oleoabundans. In a first experiment, we supplied growth medium in two different modes, fed batch and batch; for this latter we used increasing salt concentration. In the second part of the study, we tested 4 different operational modes of cultivation (batch, semicontinuous, N-limitation, N-starvation). Experiments have been performed in glass cultivation tubes. We obtained higher concentrations using batch than fed-batch, in term of maximum algal biomass (4-4.7 and 3.8 g L-1 respectively). These results showed that the fed-batch micronutrient depletion limited the growth, while high salt concentration did not affect the algal growth in the batch cultures. The second part of the study showed that the maximum biomass concentration was reached in batch N-limited condition. N-limitation resulted as the preferable culture condition in term of lipid concentration, without a substantial difference between semicontinuous and batch. These findings highlight that N. oleoabundans is a halotolerant strain thus being potentially suitable for substrates with high electrolytic concentration, including wastewater and brackish water. Moreover, our results show that N-limitation combines a good increase in the percentage of lipids with adequate biomass productivity, thus being a valid option in microalgae feeding system for energy production.