Comprehensive approach to improving life-cycle CO2 reduction efficiency of microalgal biorefineries: A review

[Display omitted] •CO2 bio-fixation capability of microalgae was comprehensively reviewed.•Carbon content of microalgae is a determinant of their CO2 fixation rate.•Biomass productivity is a highly influential factor for CO2 fixation efficiency.•It is important to minimize process energy inputs for life-cycle CO2 reduction.•Utilizing energy-efficient process elements and routes are crucial. Along with the increase in global awareness of rising CO2 levels, microalgae have attracted considerable interest as a promising CO2 reduction platforms since they exhibit outstanding biomass productivity and are capable of producing numerous valuable products. At this moment, however, two major barriers, relatively low photosynthetic CO2 fixation efficiency and necessity of carbon-intensive microalgal process, obstruct them to be practically utilized. This review suggests effective approaches to improve life-cycle CO2 reduction of microalgal biorefinery. In order to enhance photosynthetic CO2 fixation, strategies to augment carbon content and to increase biomass productivity should be considered. For reducing CO2 emissions associated with the process operations, introduction of efficient process elements, designing of energy-saving process routes, reuse of waste resources and utilization of process integration can be noteworthy options. These comprehensive strategies will provide guidance for microalgal biorefineries to become a practical CO2 reduction technology in near future.