MIXOTROPHIC AND EXTREMOPHILIC ALGAE FOR PHOTOSYNTHETIC BIOREFINERY
Wensel, Pierre Christian
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Mass outdoor cultivation of microalgae faces challenges of low productivity, contamination, inefficient CO2 supply, and difficulties in harvesting. A two-stage cultivation process was developed to address some of these challenges. This process involved culturing microalgae in a fermentor heterotrophically or photobioreactor mixotrophically as first-stage to rapidly obtain high cell densities for inoculating a phototrophic open-pond culture as second-stage. The pond system features high levels of NaHCO3, pH, and salinity. Two oleaginous, haloalkaline-tolerant, and dual-trophic green Chlorella sp. microalgae from soda lakes were isolated, identified, and compared using a multi-instrument approach as candidates for such a process. A model TAG was developed for rapid, non-destructive lipid quantitation using liquid-state 1H NMR. The two-stage cultivation system and a high pH-mediated auto-flocculation method were tested on a selected strain with a 1 L fermentor and 40 L open-tank. The effects of carbon and nitrogen sources and levels, temperature, pH, diurnal light intensity, and HCl-mediated pH control were further determined. With increasing NaHCO3 levels, cellular size and granularity increased, carotenoid/chlorophyll ratio decreased, and chlorophyll-fluorescence parameters Fv/Fm, PsiII, and NPQ remained relatively constant. Photosynthetic state transition occurred upon NaHCO3 addition. To lay the groundwork for biorefinery simulation, an industrial-scale process to convert corn-stover into succinic acid and co-products was also developed. The finite volume method of Computational Fluid Dynamics (CFD) was coupled with kinetic, stochiometric, mass, and energy balance equations using reported laboratory-scale experimental data to optimize the mixing process. This modeling approach can later be modified and used for other applications.