Air-lift bioreactors for algal growth on flue gas: Mathematical modeling and pilot-plant studies

Air-lift reactors (ALRs) have great potential for industrial bioprocesses, because of the low level and homogeneous distribution of hydrodynamic shear. One growing field of application is the flue-gas treatment using algae for the absorption of CO ₂. In this paper, we discuss the requirements for photosynthetic biomass growth in an ALR. The effects of the operating variables are analyzed using a mathematical model [Wu, X.; Merchuk, J. C. Simulation of Algae Growth in a Bench Scale Internal Loop Airlift Reactor. Chem. Eng. Sci. 2004, 59 (14), 2899] that accounts for the effects of ALR geometry, fluid flow, and illumination on the biomass growth. On the basis of the ALR principles and the specific requirements of photosynthetic processes, we developed a "triangular" ALR configuration that is particularly suitable for algal growth. We describe the design and operation of this novel bioreactor and present the first series of experimental data obtained for two different algal species in a pilot-scale unit supplied with flue gases from a small power plant. The measured removal efficiency of CO ₂ was significant (82.3 ± 12.5% on sunny days and 50.1 ± 6.5% on cloudy days) and consistent with the increase in the algal biomass.