Carbon dioxide (CO
2) is one of the most important
contributors for the in
crease of the greenhouse effe
ct. CO
2 con
centrations are in
creasing in the last de
cades mainly due to the in
crease of anthropogeni
c emissions. To redu
ce the effe
cts
caused by this environmental problem, several te
chnologies were studied to
capture CO
2 from large emission sour
ce points: (i) absorption; (ii) adsorption; (iii) gas-separation membranes; and (iv)
cryogeni
c distillation. The resulting streams with high CO
2 con
centrations are transported and stored in geologi
cal formations. However, these methodologies, known as
carbon
capture and storage (CCS) te
chnologies, are
considered as short-term solutions, as there are still
con
cerns about the environmental sustainability of these pro
cesses.
A promising technology is the biological capture of CO2 using microalgae. These microorganisms can fix CO2 using solar energy with efficiency ten times greater than terrestrial plants. Moreover, the capture process using microalgae has the following advantages: (i) being an environmental sustainable method; (ii) using directly the solar energy; and (iii) co-producing high added value materials based on biomass, such as human food, animal feed mainly for aquaculture, cosmetics, medical drugs, fertilizers, biomolecules for specific applications and biofuels. Approaches for making CO2 fixation by microalgae economically competitive in comparison with CCS methodologies are discussed, which includes the type of bioreactors, the key process parameters, the gaseous effluents and wastewater treatment, the harvesting methods and the products extracted by microalgal biomass.
