Microalgae have been considered a promising option to provide food, feed and biofuel based on their high areal productivity and their ability to be cultured on non-arable land with different water sources (fresh, brackish or seawater). This research thesis work evaluated different cultivation systems for growing the marine microalga Tetraselmis sp.(M8) and optimised dispersed air flotation (DiAF) as a separation and harvesting method using the research facilities in the Algae Biotechnology Laboratory and Mineral Processing Laboratory at the University of Queensland’s St. Lucia campus.

Current algae cultivation systems are threatened by contamination with other algae or algal grazers resulting in the need for significant improvement in cultivation and harvesting systems. So far, not much work has been carried out on flotation methods, a process widely used for recovery of particles in mining, for harvesting of marine microalgae. To address these issues, we have developed an efficient two-stage cultivation system using the marine microalga Tetraselmis sp. M8. This hybrid system combines exponential biomass production in positive pressure air lift-driven bioreactors with a separate synchronised high lipid induction phase in nutrient deplete open raceway ponds. A comparison to either bioreactor or open raceway pond cultivation systems suggests that this process potentially leads to significantly higher productivity of algal lipids that can serve as a feedstock for biodiesel production. Nutrients are only added to the closed bioreactors and open raceway ponds have turnovers of only a few days, thus avoiding the critical issue of contamination.