11. Enhanced Fixation of CO₂ in Land and Aquatic Biomass

Biomass, either terrestrial or aquatic, can efficiently fix CO₂ from a variety of sources, such as the atmosphere, power plant and industrial exhaust gases, and soluble (hydrogen)carbonate salts thanks to the enzyme Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). In addition to the carboxylation of ribulose that fixes CO₂ into glucose (ca. 60%), used by the biomass as a source of energy and for building cellulose, RuBisCO also oxidizes the substrate (ca. 40%). Attempts have been made to engineer the enzyme for an enhanced carboxylation. Besides, efficient light-using organisms are under deep investigation. In particular, enhanced bio-fixation using microalgae has recently become an attractive approach to CO₂ capture and C-recycling with a benefit derived from downstream utilization and application of the resulting microalgal biomass. This is a paradigmatic example of use of water and CO₂ for stepping from the linear- to the circular-C-economy. It is of importance to select appropriate microalgal species that have a high growth rate, high CO₂ fixation ability into valuable components, resistance to contaminants, low operation cost, and are easy to harvest and process. Strategies for the enhanced production of bioproducts and biofuels from microalgae, based on the manipulation of the strain physiology by controlling light, nutrient and other environmental conditions, which determine an efficient carbon conversion, are underway since long time. They are discussed in this Chapter together with an assessment of the value of the algal strain P. Tricornutum.