UBC Theses and Dissertations
Growth optimization of Synechococcus sp. PCC7002 in laboratory photobioreactors Wu, Tong
Microalgae have the potential to be a significant source of renewable energy. Microalgae reduce CO₂ emissions by consuming it via photosynthesis, and provide a cheap option to produce high value biological products. Synechococcus sp. PCC7002 is a microalga strain that possesses all of these potentials, and can be easily genetically modified. To utilize these potentials of Synechococcus sp. PCC7002, a method to optimize its growth in terms of a high biomass concentration and a high growth rate needs to be implemented. To achieve this objective, shake flask scale experiments, as well as reactor scale experiments were designed and conducted. 250 mL shake flasks with 100 mL of medium were used for the flask experiments. In the first experiment, the A+ medium was investigated. The optimal concentrations of the three important nutrient components, NaNO₃, FeCl₃, and KH₂PO₄ to achieve highest Xmax were determined to be 23.5 mM, 0.028 mM, and 0.72 mM respectively. The optimal concentrations to achieve highest µmax were 5.88 mM, 0.007 mM, and 0.18 mM respectively. Another factorial experiment regarding the effects of temperature and light intensity was carried out next. The optimal conditions within the tested range were determined to be 35˚C, 250µE/m²/s for maximum biomass concentration, and 35˚C, 150 µE/m²/s for maximum specific growth rate. The effects of inlet CO₂ concentrations were studied in the large scale continuously aerated reactor. The optimal concentration of CO₂ was found to be 8% by volume, and 3.1 g/L biomass concentration and 0.0186 hr-¹ maximum specific growth rate were achieved under this condition. Further increase in inlet CO₂ concentration led to a decrease in biomass concentration due to the lower pH associated with the higher carbonic acid concentration in the medium. Lastly, an experiment was completed using the recombinant strain, with a very good growth rate obtained at 33˚C, 300 µE/m²/s, and 0.5 L/min inlet gas with 10% CO₂. Under this condition, a maximum biomass concentration of 3.1 g/L, and a maximum specific growth rate of 0.0180 hr-¹ were achieved.
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