The fuel crisis with the slumping reserves of fossil fuels and the exponential increase in the demand of energy necessitate a paradigm shift to a more sustainable and eco-friendly energy system. Microalgal biofuel has been recognized as one of the most prominent and versatile alternative renewable energy sources because it can be converted into a wide array of biofuels, such as biodiesel, bioethanol, bioelectricity and biogases such as syngas, methane, hydrogen, and hythane etc., with a lower carbon emission profile. To attain the economic viability of algal fuels, a collective biorefinery approach addressing both the operational and technical limitations is quintessential. The current review critically analyzes and categorizes energy aspects of microalgae through various direct and indirect approaches with the perspective of a circular economy. These approaches include complicated thermochemical and biochemical processes integrating the recovery of a wide range of value-added products apart from biofuels, thus defining a cascading approach for a multiproduct-based biorefinery model. A glimpse of recent technological advancements comprising hybrid cultivation systems, prospects of co-culturing, and the role of automated/modeling approaches in the industrial-scale production of "algal-based bioenergy" is also discussed in detail. Further, the review has also scrutinized and highlighted the developments and bottlenecks in genetic and molecular aspects of strain improvement for bioenergy production. Furthermore, the study also correlated the socioeconomic and environmental impacts of producing this green energy by evaluating the prospects and pitfalls to obtain a holistic picture on this alternative fuel for a bio-based sustainable economy.

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