Microalgal cell factories for bioenergy and climate action: a circular bioeconomy roadmap.

Microalgae represent a crucial, multifunctional microbial cell factory platform for renewable energy and climate change mitigation. Their notably high lipid content (often exceeding 70% DCW) and rapid growth rates, which significantly surpass those of traditional terrestrial crops, making them an ideal feedstock for diverse bioenergy applications. This review critically evaluates advanced conversion pathways for biofuels such as biodiesel and bioethanol, as well as biohydrogen production and bioelectricity generation via microbial fuel cell technology. It further explores key technical paradigms, including photobioreactor and open-pond cultivation systems, extraction techniques, and the critical role of transesterification for biodiesel synthesis. Uniquely, microalgae synergistically sequester atmospheric carbon dioxide (CO2) during the photosynthetic process and remediate nutrient-rich wastewater, positioning them as an effective feedstock model within a circular bioeconomy framework. Finally, this work delineates persistent techno-economic hurdles, such as high operational costs and harvesting inefficiencies, while proposing strategic future research directions in genetic engineering and system integration necessary to achieve global commercial scalability.