Air-Lift Bioreactors for Algal Growth on Flue Gas:  Mathematical Modeling and Pilot-Plant Studies

Abstract

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.

Design principles of photo‐bioreactors for cultivation of microalgae

“…A straight forward way to come to a rational engineering approach for photo-bioreactor design requires the simulation of three phase fluid dynamics including bubbles and cell trajectories [58][59][60], calculating light transfer and attenuation by ray tracing methods [61] and finally coupling these to physiological kinetic and dynamic cell models [62,63]. In this way, possible deficiencies in axial gas transfer or the frequency of vortices can be calculated beforehand.…”

“…The measurement of chlorophyll and photosynthetic efficiency (F V / F m by PAM sensors) is becoming a standard. In current biophysical developments alga strains with reduced antenna size are developed, which should absorb only the light that can actually be used [60]. Whether or not these algae are really the solution for the light diffusion problem depends on the cell density and other factors.…”

Biofuels from Microalgae

“…44 A higher CO 2 mitigation rate between 50.1 AE 6.5% on cloudy days and 82.3 AE 12.5% on sunny days was reported by other researchers using different algal species. 45 Depending on the microalgal species and condition used in the facilities, algal biomass produced could be further processed for biodiesel, bio-oil, and bio-syngas production.…”

The Challenge of Bioenergies: An Overview

“…This is mainly because of their abilities to accumulate high amounts of intracellular lipids, their relatively fast growth rates and their similarities of oil composition with plants (Kalscheuer et al, 2006a(Kalscheuer et al, , 2006b). Microalgae are often used for the sequestration and recycling of CO 2 by "CO 2 filtration" (Haag, 2007) and can reduce CO 2 exhaust by 82% on sunny days and by 50% on cloudy days (Vunjak-Novakovic et al, 2005). This process is much more elegant than carbon storage (CCS) in depleted oil fields or in aquifers because the carbon can be recycled via microdiesel.…”