Effect of carbon dioxide on biomass and lipid production of Chlorella pyrenoidosa in a membrane bioreactor with gas-liquid separation

In this work, an immobilized-cell biofilm photo-bioreactor, in which the CO2-rich gaseous phase was separated from the nutrient-rich liquid phase by a polytetrafluoroethylene membrane, was proposed to enhance the adsorption of CO2 by algal cells and the formation of biofilm on the membrane surface by reducing the disturbance from bubbles. The biomass productivity and biochemical composition, CO2 removal efficiency, and fatty acid profile were measured to evaluate effect of CO2 concentration on biomass and lipid production for biotechnological applications of the photo-bioreactor. The maximal biomass productivity (4.06 g/m2/d), lipid productivity (0.64 g/m2/d), and CO2 removal efficiency (52.5%) were obtained at 3% CO2 concentration, and C16-C18 fatty acids in this cultivated biofilm accounted for 96.28% to 98.61% of the total fatty acids in all runs. The results indicate that the productivities of lipid and biomass were significantly improved using the immobilized-cell cultivation method.