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Photosynthetic production of microalgal biomass production for fuels, feeds, foods and other low-cost commodities will also require low-cost sources of CO2. Unlike higher plants, microalgae have low access to atmospheric CO2 due to the low mass transfer rate from CO2(gas) to CO2(aqueous), resulting in limited algae growth. Thus, most research in this field has focused on concentrated CO2 sources, in particular CO2 from the flue gases of fossil-fueled power plants. However, the transport of the flue gases (containing from about 3-13% CO2) from source to the algal production site must be limited to a few kilometers due to cost. The alternative for longer distance transport - also expensive - is to concentrate the flue gas CO2 by chemical processes. More concentrated, sources of CO2 are also available, such as from refineries, fertilizer and other chemical plants, ethanol fermentations, anaerobic digestion of wastes, among others. Microalgae can be cultivated on organic wastes, which provide both nutrients (N, P, K, etc.) and organic and inorganic carbon for algal growth. Finally, direct capture of CO2 from air by the algal cultivation system may be possible, or it could be coupled to an air-capture process. The relative productivities, economics, greenhouse gas balances, and resource potentials of these alternative CO2 sources for large-scale production of microalgae are reviewed. A case example will be presented for a currently ongoing project for utilization of CO2 from a coal-fired power plant in Orlando Florida, for production of biofuels, animal feeds and wastewater treatment. Annual productivities of filamentous algae and their feed nutritional value will be presented.