(254d) Integrating Photo-Bioreactor and Fermentor to Produce Biofuels and Bioelectricity

We have investigated simultaneous production of biofuels and bioelectricity from an integrated bioreactor that combines photo-synthesis and fermentation.  In the integrated bioreactor, a fermentor and a photo-bioreactor were combined in a way that the carbon dioxide produced in the fermentation can be used to grow algae in the photo-bioreactor. Also, the reactors were attached to a proton exchange membrane in between so that they form a biological fuel cell. To synchronize the carbon dioxide production in the fermentation and the carbon dioxide utilization in photo-synthesis, the fermentor was run continuously but the photo-bioreactor was run in batch mode.  An autotrophic microalgae, Chlorella vulgaris, and a bear yeast, Saccharomyces bayanus, were grown in the photo-bioreactor and in the fermentor, respectively. The ethanol production by the yeast, oil production by the algae, and electricity generation were monitored over time. The electricity generation was characterized by potentiodynamic polarization. In a two-liter size integrated bioreactor, we observed an ethanol productivity of 0.49±0.37 g l^-1 hr^-1, algae oil productivity 2.5 mg l^-1 hr^-1, power density of 70.61 ± 12.41 mW/m² of the electrode, and current density of 155.02 ± 31.23 mA/m².  Preliminary scale-up studies show a great potential for this integrated system.