Optimization of growth conditions toward two-stage cultivation for lipid production of chlorella vulgaris

Increasing concerns about limited fossil fuel and elevated level of atmospheric carbon dioxide are driving force to develop renewable biofuels, and microalgae are considered a particularly promising feedstock for industrialized biofuel due to their inherent advantages. It is imperative to further optimize the growth conditions in order to achieve maximal algal biomass productivity and low down the cost of microalgal biomass production. The research in this project aimed to enhance lipid production of Chlorella vulgaris by optimizing the nutrient supply and growth conditions. The effects of temperature, nitrogen concentration and initial cell density on neutral lipid productivity were evaluated and optimized by response surface method with a 17-run Box-Behnken design (BBD). With the increase of temperature from 20 to 30°C, the neutral lipid productivity increased up to its peak value at 27°C. However, the 2D contour lines showed the temperature has a significant effect on neutral lipid productivity compared with those of cell density and/or nitrogen concentration. The optimal conditions for the algal growth are 1.5 g L^-1 of nitrogen concentration and 50% of cell density at 27.4°C. The optimal lipid productivity obtained from the experiment was in agreement with the model prediction, confirming the validity of the model.