Microalgae: a robust “green bio-bridge” between energy and environment

Microalgae are a potential candidate for biofuel production and environmental treatment because of their specific characteristics (e.g. fast growth, carbon neutral and rich lipid accumulations). However, several primary bottlenecks still exist in current technologies, including low biomass conversion efficiency, bio-invasion from external environment, limited or costly nutrient sources, and high energy and capital input for harvest, stalling its industrial progression. Coupling biofuel production with environmental treatment makes microalgae a more feasible feedstock. This review focuses on microalgal biotechnologies for both bioenergy generation and environmental treatment (e.g. CO 2 sequestration and wastewater reclamation). Different intelligent technologies have been developed, especially during the last decade, to unclog the bottlenecks, including mixotrophic/heterotrophic cultivation, immobilization, and co-cultivation. It has been realized that any single purpose for the cultivation of microalgae is not an economically feasible option. Combinations of applications in biorefineries are gradually reckoned to be necessary as it provides more economically feasible and environmentally sustainable operations. This presents microalgae as a special niche occupier linking the fields of energy and environmental sciences and technologies. The integrated application of microalgae is also proven by most of the life-cycle analysis (LCA) studies. This study summarizes the latest development of primary microalgal biotechnologies in the two areas that will bring researchers a comprehensive view towards industrialization with an economic perspective.