7 - Carbon dioxide capture and its use to produce microalgae-based fuels

Abstract

Microalgae are photosynthetic microorganisms with the capability to fix CO2 in an accelerated and efficient manner because they have a simple cellular structure and fast metabolism. In natural water bodies, the growth of microalgae is maintained by the diffusion of carbon dioxide from air to water. Nevertheless, in mass cultures (cellular concentration >1gL−1), CO2 must be added to avoid growth limitation. The necessity of a large amount of CO2 in concentrated cultures enables microalgal cultures to reduce the emissions of specific CO2 sources such as chimneys or boilers by transporting the exhaust flue gases to microalgal cultures to promote the biological fixation of CO2. However, the process presents different limitations (physiological, technical, operative, etc.), many of which can be solved by the optimization of the process or by strain selection (resistant to high concentrations of CO2 or tolerant to the presence of contaminants). Nevertheless, the development of industrial CO2 biofixation processes has been slowed by financial constraints because the market value of the biomass (as animal feed) is very low. Economic feasibility can be reached by including the biofixation process into a biorefinery concept to obtain high-value products such as pigments, carbohydrates, proteins, antioxidants, etc.; the process can also be included in the production of biofuels such as biodiesel, aviation fuel, biohydrogen, and bio-oil. This chapter analyzes the potential of microalgae and cyanobacteria to conduct the biofixation of CO2 and the linkage of this process to biofuel production.