Application of experimental design methodology for optimization of biofuel production from microalgae

Optimization of biofuel productivity, in terms of lipid content, polysaccharide content, and calorific value, from microalgae was performed by varying four variables (temperature, light intensity, nitrogen content, and CO2 addition) using a 24 full factorial design. A statistical analysis showing the influence of each variable and their interactions was conducted. The selected variables all influence biofuel productivity, but their importance varies according to the sequence: CO2 addition > temperature > nitrogen content > light intensity. Interactive effects of temperature with light intensity and nitrogen with CO2 addition for lipid and polysaccharide productivities were identified, respectively. For calorific value, interactive effects of CO2 addition with light intensity and nitrogen content were observed. The highest biofuel productivity was obtained at the following conditions: temperature (>25 °C), light intensity (>60 μmol photons m−2 s−1), nitrogen content (<50 mg L−1), and CO2 addition (>18 mL L−1 d−1). 10 days was found to be the most favorable cultivation time for lipid production under the investigated conditions.