Cultivation of microalgae for oil production with a cultivation strategy of urea limitation.

The microalgae, Chlorella sp., were cultivated in various culture modes to assess biomass and lipid productivity in this study. In the batch mode, the biomass concentrations and lipid content of Chlorella sp. cultivated in a medium containing 0.025-0.200 g L(-1) urea were 0.464-2.027 g L(-1) and 0.661-0.326 g g(-1), respectively. The maximum lipid productivity of 0.124 g d(-1)L(-1) occurred in a medium containing 0.100 g L(-1) urea. In the fed-batch cultivation, the highest lipid content was obtained by feeding 0.025 g L(-1) of urea during the stationary phase, but the lipid productivity was not significantly increased. However, a semi-continuous process was carried out by harvesting the culture and renewing urea at 0.025 g L(-1) each time when the cultivation achieved the early stationary phase. The maximum lipid productivity of 0.139 g d(-1)L(-1) in the semi-continuous culture was highest in comparison with those in the batch and fed-batch cultivations.