Effect of light, CO₂ and nitrate concentration on Chlorella vulgaris growth and composition in a flat-plate photobioreactor

The utilization of microalgal biomass for the production of biodiesel and bioethanol is viewed as a promising alternative to increase the offer of both biofuels in the future. In view of this, the autotrophic growth of the green microalga Chlorella vulgaris in a flat-plate photobioreactor was evaluated along with physiological characteristics, such as lipid and carbohydrate composition, and auxiliary parameters of the cultivation using response surface methodology (RSM). Mean biomass productivities of up to 0.262 ± 0.006 g L^-1 day^-1 were obtained with maximum light intensity and intermediate CO₂ concentrations and the microalgal biomass averaged carbohydrate and lipid contents of 8% and 32% respectively. The light flux supplied to the cultivations and the amount of CO₂ in the feed gas are variables with significant effect on the mean biomass productivity of the microalgae and help estimate the maximum final biomass concentration possible to be obtained. The behavior of associated parameters, such as increase in medium pH and O₂ evolution, was measured and both varied according to different cultivation conditions. (author)