Advancements on process regulation for microalgae-based carbon neutrality and biodiesel production

Microalgae biotechnology is a promising pathway to cope with CO2 emission and energy crisis due to high CO2 fixation rate and lipids productivity. However, bottlenecks of high energy cost, low photosynthetic efficiency and poor economic feasibility severely hinder its commercialization. Understanding process mechanisms of microalgae photosynthetic CO2 fixation and lipids production, and thus seeking possible regulations to enhance weak links are potential process regulation strategy for augmented competitiveness. Firstly, mass transfer and conversion processes of microalgae photosynthesis involving CO2 and light were comprehensively illuminated in this review. In detail, mechanisms of CO2 and light transfer in microalgae suspension, bioavailable carbon and photon assimilation by microalgae cells, as well as intracellular mass conversion were illustrated. Besides, synergistic effects of light and CO2 on microalgae photosynthesis were depicted from perspective of electrons and protons supply-demand relationships between photosynthetic photo-reaction and dark-reaction steps in chlorophyll. Possible weak links in these processes were emphasized to provide guideline for regulation. Secondly, available regulation strategies for CO2 and light mass transfer, cellular assimilation and intracellular conversion were summarized. Subsequently, economic and environmental impacts of process regulation on microalgae CO2 fixation and biodiesel output were evaluated to lit up large-scale applicability. Finally, challenges and future directions of microalgae biotechnology were described to inspire in-depth research and engineering practice. This review may provide a novel process regulation standpoint for operating microalgae-based CO2 fixation and biodiesel production in the most efficient manner, further facilitating the applicability of microalgae biotechnology towards carbon neutrality and biodiesel production. •Microalgae CO2 fixation are reviewed from perspectives of mass transfer.•CO2 transfer from gas stream to microalgae suspension is major bottleneck.•Uneven light distribution greatly hindered microalgae photosynthesis efficiency.•Strategies to regulate photo- and dark-reactions during photosynthesis are vital.