Comparative analysis of top-lit bubble column and gas-lift bioreactors for microalgae-sourced biodiesel production

The development of top-lit one-meter deep bioreactors operated as either a gas-lift or bubble column system using air and carbon dioxide enriched air was studied. The goal was high productivity cultivation of algae with elevated lipid levels suitable for conversion into biodiesel. A theoretical energy requirement analysis and a hydrodynamic model were developed to predict liquid circulation velocities in the gas lift bioreactor, which agreed well with experimental measurements. The influence of operational parameters such as design of bioreactor, gas flow rates and carbon dioxide concentration on the growth and lipid volumetric production of Scenedesmus dimorphus was evaluated using factorial design. While bio-mass productivity was 12% higher in the bubble column bioreactor (68.2 g(dw) m(-2) day(-1)), maximum lipid volumetric production (0.19 g(Lipid) L-1) was found in a gas-lift bioreactor sparged with 6% carbon dioxide due to hydrodynamic and light stresses. (C) 2016 Elsevier Ltd. All rights reserved.