Optimization of Growth and Hydrocarbon Production from a Green Microalga Botryococcus braunii by Plackett-Burman Design and Response Surface Methodology

Abstract

Statistical experimental designs were used to optimize the culture conditions on growth and hydrocarbon production from a green microalga Botryococcus braunii J4-1. In the optimization process, seven independent variables—NaNO3, KH2PO4, Fe-citrate, pH, NaHCO3, CO2 and light intensity—were screened to verify the three most critical variables by the Plackett-Burman design. Fe-citrate, pH and CO2 were then selected for further optimization by central composite design coupled with response surface methodology. Seventeen experimental tests were run under five levels of the significant variables. The influence of these variables on the responses of biomass, chlorophyll and hydrocarbon was evaluated using a second-order polynomial multiple regression model. Analysis of variance showed a high correlation coefficient of determination value of more than 0.90 and the P-values were less than 0.05. These values indicated that the model had a good fit and was acceptable at this level of significance. The optimum values of the variables were Fe-citrate 1.5 mg.L-1, pH 6.8 and CO2 2.5% (volume per volume) gave maximum yield of biomass at 5.74 g.L-1, 13.51 mg.L-1 of chlorophyll and hydrocarbon 1.44 g.L-1. Validation of the experimental values using the optimal conditions showed that the experimental values were quite close to the predicted values. Furthermore, the corresponding results of the deviations for the production of biomass, chlorophyll and hydrocarbon were 10.17, 11.19 and 1.41%, respectively, suggesting that the experimental designs used in this work were effective for the optimization of the process parameters on biomass, chlorophyll and hydrocarbon production.