Cultivation of Chlorella protothecoides in photobioreactors: The combined impact of photoperiod and CO 2 concentration

Algal biomass is regarded as an alternative source for producing renewable fuels, given the chemical nature of storage products: lipids, starch, and proteins. Many factors affecting the production of microalgal biomass and lipid accumulation include the light and CO 2 concentration, i.e. critical factors for determination of the biochemical composition of microalgal biomass. Our objective was to evaluate the effect of three different light/dark photoperiods (12/12 h, 16/8 h, 24/0 h) and the CO 2 concentration (from air and 5% v/v CO 2 ‐enriched air) on the growth rate, productivity, and changes in the biochemical composition of Chlorella protothecoides biomass. Continuous illumination stimulated growth under supplementation of air CO 2 . At 5% CO 2 , the maximum C. protothecoides growth rate was found under 16/8 light/dark cycles and longer duration of light yielded a decrease in the specific growth rate. The photoperiods and CO 2 concentrations influenced the biomass productivity. Chlorella protothecoides produced biomass more efficiently at the 24/0 and 16/8 light/dark cycles under supplementation of air CO 2 than at addition of 5% CO 2 . However, under the 12/12 light/dark cycle, biomass productivity was higher at 5% CO 2 . The light photoperiod greater than 16 h did not increase biomass productivity. These factors also influenced the content of lipids and carbohydrates. A maximal lipid content was observed for the 24‐h photoperiod for air CO 2 , whereas the addition of 5% CO 2 affected lipid and carbohydrate production.