Optimizing carbon dioxide utilization for microalgae biofilm cultivation

The loss of carbon dioxide (CO₂ ) to the environment during microalgae cultivation is undesirable for both environmental and economic reasons. In this study, a phototrophic biofilm growth model was developed and validated with the objective to maximize both CO₂ utilization efficiency and production of microalgae in biofilms. The model was validated in growth experiments with CO₂ as the limiting substrate. The CO₂ utilization and biomass productivity were maximized by changing the gas flow rate, the number of biofilm reactors in series and gas composition. Based on simulations, the maximum CO₂ utilization efficiency that was reached was 96% based on a process employing flue gas. The corresponding drop in productivity was only 2% in comparison to the non-CO₂ limited reference situation. In order to achieve this, 25 biofilm reactors units, or more, must be operated in series. Based on these results, it was concluded that concentrated CO₂ streams and plug flow behavior of the gaseous phase over the biofilm surface are essential for high productivity and CO₂ utilization efficiency. Biotechnol. Bioeng. 2017;114: 769-776. © 2016 Wiley Periodicals, Inc.