The overall hypothesis tested in this research was that microalgae are an efficient
method for power-plant flue-gas CO2 mitigation and bio-energy production. Research examined the losses of organic matter from algal cells, finding that potentially significant quantities of organic carbon and energy may be lost in this manner. The work also examined the energy balance of laboratory-scale gas-sparged photobioreactors. Manipulation of the power input for gas-sparging influenced the productivity and net energy balance of photobioreactors, and it was concluded that optimization of power input to microalgal photobioreactors had significant implications for the environmental impacts and sustainability of technologies. The effect of nitrogen source (nitrate, urea, ammonium) on the productivity of microalgae was tested. It was found that the nitrogen source supplied did not impact growth under the test conditions. However, measurements of nitrogen dynamics in intensive bubble column photobioreactors showed that supply of fertilizer nitrogen was an important energy burden in the production of microalgal biomass. The long-term cultivation of Scenedesmus obliquus in an outdoor tubular photobioreactor was achieved in a cooltemperate
climate, with productivity comparable to the literature. The evidence from
this research showed that it is important to design microalgal cultivation systems in such a way that a significant positive energy return may be achieved for any given global location. The anaerobic co-digestion of microalgal biomass with cellulose yielded significant quantities of H2, showing that a mixture of microalgal biomass and cellulose improved yields of gas. The overall conclusion from the work was that microalgal technologies have significant potential for CO2 mitigation and bio-energy, but that it will require significant research aimed at reducing the energetic demands of production to improve net energy production from these systems.