Development and optimization of algal cultivation systems

This thesis describes research done on two novel algae cultivation systems. The first system was an attached algal growth system to facilitate biomass harvest with improved biomass yield. In the attached system, algal cells were grown on the surface of a material rotating between the nutrient-rich liquid phase and the carbon dioxide-rich gaseous phase. The algal cells from the attached growth system were harvested by simply scraping off the algal biofilm. The operation conditions of the attached growth system were optimized to improve biomass productivity. A harvesting frequency of 7 days with a rotational speed of 4 rpm resulted in the highest cell productivity. Changing the CO2 content from atmospheric CO2 level (~300ppm) to 3000 ppm did not significantly change growth performance. The attached growth system resulted in a biomass productivity of 10.5 g*m -2 *day -1 . The biomass harvested from the attached system had higher carbohydrate content, but lower lipid content compared to the suspension culture system. Other research presented in this thesis was to grow the microalga Chlorella vulgaris under simulated microgravity conditions to evaluate CO2 consumption and O2 generation rates. The effects of hydraulic retention time, gas flow rate, and CO2 concentration on algal growth were investigated. All the three factors significantly influenced CO2 consumption and O2 generation rates. A statistical response surface design was used to optimize these two parameters. The optimal conditions for CO2 consumption and O2 generation were determined to be 6.59 days hydraulic retention time, 0.153 vvm gas flow rate, and 0.80% CO2 concentration. Algae growth and CO2 consumption rates in microgravity were not significantly different than growth at earth (1 g) gravity. A hollow fibre membrane photobioreactor was also developed which enhanced CO2 consumption rates.