Focusing on the Optimization for Scale up in Airlift Bioreactors and the Production of Chlamydomonas reinhardtii as a Model Microorganism

The aim of this work is to use optimization as a tool for scale up in airlift bioreactors and apply this approach to a real life process. To put this approach into practice, Chlamydomonas reinhardtii, a green microalgae, was used as a model microorganism. The effects of the design parameters on the performance of the bioreactors were monitored through the changes in mixing and circulation times. As the first step, the effective parameters (draft tube diameter and height, water level over the draft tube, volumetric flow rate of air, and sparger-draft tube distance) in the 1.1 L airlift bioreactor were determined and optimized by the 5-factor, 3-level Box-Behnken design for response surface methodology. A draft tube with a 38-250 mm dimension was selected resulting in a mixing time of 9.94 s with a 1.05 L min-1 air flow rate. In the second step the optimized values were applied to a larger airlift bioreactor of 11 L for C. reinhardtii productions. Comparable biomass productivities (0.87-0.90 g L-1 day-1) and doubling times (25-27 h) in both systems was a good indication of the success of the scale-up approach.