3rd Generation Biofuels - Chapter 14, Biofuels and chemicals from microalgae

Microalgae, photosynthetic microorganisms, grow rapidly (a few days for an entire growth cycle) and easily in harsh living conditions due to their simple cellular structure. Under sunlight, they utilize CO2, a greenhouse gas, as a carbon source, simple nutrients, e.g., contaminants in water (NH4 +, NO3 −, PO4 3−), and water that could be unsuitable for human consumption (wastewater, seawater). Various high-value chemical compounds (pigments, antioxidants, polysaccharides, fatty acids, vitamins, etc.) with their proportions depending upon microalgae species and strains can be extracted for a number of industrial applications (biofuels for transportation, pharmaceuticals, food, e.g., nutrient supplements and cosmetics). Lipid content in microalgae, which can be up to 75%wt of biomass, together with a significant proportion of saturated and unsaturated free fatty acids of 12–22 carbon atoms, can be used for biofuel production, e.g., via transesterification. Biomass residues left over from the extraction process can be used for fertilizers (high N:P ratio) and/or generating chemicals, e.g., ethanol and methane. This chapter will focus on the current state-of-the art technologies applied for the extraction of compounds from microalgae/pretreatment and downstream processing for biofuels and chemicals from microalgae. Challenges will be discussed in detail alongside future development of integrated approaches for biofuels and chemicals from microalgae.