Comparsion of Marine Microalgae Culture Systems for Fuels Production and Carbon Sequestration

70302S02-II Microalgae technologies that produce renewable fuels and utilize the CO2 from power plant flue gases are one potential approach to the mitigation of greenhouse gases. However, to be useful, high solar energy conversion efficiencies by large-scale algal mass cultures will be required. This project will develop a biotechnological approach that combines mass culture optimization with superior algal strains to achieve the very high productivities required. The selected strains will be combined with improved pond operating conditions to result in very-high-yield mass cultures able to utilize large amounts of CO2 and to produce biofuels and higher value co-products. In Phase I, three different microalgae production systems ¿ open shallow raceway ponds, vertical circular tanks and tubes, and a flat-plate closed photobioreactor-were operated with marine algal species. There were no unexpected productivity differences between these photobioreactors. The vertical systems had a higher productivity per unit of intercepted light (photosynthetic efficiency), but the ponds had an overall higher productivity per unit of land area covered. Surprisingly, partially covered open ponds also exhibited high photosynthetic efficiencies, suggesting that productivities are limited not only by light saturation but also by photoinhibition. The results of Phase I suggest that mutant strains with reduced "light harvesting" chlorophyll would be much more productive in mass cultures than the normal (parental or "wild-type") strains. Therefore, in Phase II, such mutants will be developed and tested in outdoor pond and photobioreactor systems to demonstrate the potential for high productivities (100 metric tons/hectare-year and above). Commercial Applications and Other Benefits as described by awardee: The immediate applications of this process should be in marine microalgae mass cultures that combine biomass production for conversion to biofuels and greenhouse gas abatement with higher-value co-products, such as animal feeds. More broadly, the high-productivity microalgae processes also should be applicable in wastewater treatment, agricultural nutrient recycling and biofertilizers, and commodity chemicals and feed production.