A Review: Microalgae and Their Applications in CO2 Capture and Renewable Energy

Fossil fuels, which are recognized as unsustainable sources of energy, are continuously consumed and decreased with increasing fuel demands. Microalgae have great potential as renewable fuel sources because they possess rapid growth rate and the ability to store high-quality lipids and carbohydrates inside their cells for biofuel production. Microalgae can be cultivated on opened or closed systems and require nutrients and CO2 that may be supplied from wastewater and fossil fuel combustion. In addition, CO2 capture via photosynthesis to directly fix carbon into microalgae has also attracted the attention of researchers. The conversion of CO2 into chemical and fuel (energy) products without pollution via this approach is a promising way to not only reduce CO2 emissions but also generate more economic value. The harvested microalgal biomass can be converted into biofuel products, such as biohydrogen, biodiesel, biomethanol, bioethanol, biobutanol and biohydrocarbons. Thus, microalgal cultivation can contribute to CO2 fixation and can be a source of biofuels. This article reviews the literature on microalgae that were cultivated using captured CO2, technologies related to the production of biofuels from microalgae and the possible commercialization of microalgae-based biofuels to demonstrate the potential of microalgae. In this respect, a number of relevant topics are addressed: the nature of microalgae (e.g., species and composition); CO2 capture via microalgae; the techniques for microalgal cultivation, harvesting and pretreatment; and the techniques for lipid extraction and biofuel production. The strategies for biofuel commercialization are proposed as well.