Microalgal cultivation with waste streams and metabolic constraints to triacylglycerides accumulation for biofuel production

Global increases in the generation of waste streams, including liquid, gaseous, and solid waste, have been posing serious challenges for waste management as a result of their potential impacts on receiving environments and climate change. The conversion of waste streams into useful bioenergy, biofuels, and bioproducts through recycling and/or recovery has been presented as a promising alternative. Coupling the bioremediation of waste streams with microalgae-based biofuel production, offers an alternative strategy to achieve waste-to-biofuel and bioenergy. A group of unicellular photosynthetic eukaryotes, microalgae require relatively simple nutrients and inorganic carbon sources to support their growth, while accumulating several biofuel precursors, such as starch or storage lipids. This review summarizes the current approaches to microalgal biomass production using waste streams, including waste-water; waste or CO2-enriched gas (flue gas and biogas); waste organics (i.e., crude glycerol); and waste heat, as well as the primary common operational challenges and corresponding mitigation strategies involved in cultivation approaches. Moreover, microalgal metabolic pathways supporting the biosynthesis of energy-rich molecules such as triacylglycerides (TAG) and starch are discussed. Metabolic constraints and potential approaches for the enhancement of microalgal TAG accumulation are systematically and critically analyzed. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd.