Regulation mechanisms for simultaneous rapid carbon sequestration and premium biomass production.

Carbon fixation potential critically determines the overall performance, scalability, and economic viability of biological carbon utilization systems. Recently, microalgal attached carbon fixation systems have attracted worldwide attention for their high fixation efficiency and biomass yield. However, challenges remain due to insufficient mechanistic understanding to guide further improvements, alongside unpredictable biomass quality changes from trade-offs. This study developed a positive regulation strategy to boost carbon fixation and biomass production in Chlorella pyrenoidosa while clarifying the carbon allocation mechanisms. Results showed a peak carbon fixation rate of 9.68 g CO2/L reactor/d, a final CO2 fixation efficiency of 27 %, and a dried biomass yield of 10.26 g/L, representing 38-, 5-, and 81-fold increases over the control. Notably, protein and lipid contents reached 545 and 174 mg/g, which were 1.30- and 2.06-fold higher than the control. The favorable results were attributed to: (i) enhanced carbon fixation resulted from rapid photosynthetic initiation, where regulated CO2 boosted photosynthesis 2.62 folds through improved electron transfer, and attachment raised it 2.98 folds via enhancing mass transfer and photon utilization; (ii) premium biomass was supported by preserved chlorophyll and photosystem II activity, yielding 4.24- and 5.23-fold higher photosynthetic efficiency than in unregulated nutrients and no phosphate buffer systems; and (iii) reactive oxygen species served as early signals promoting initial adhesion and microhabitat stability, while subsequent redox balance prevented oxidative damage and maintained metabolic activity. Therefore, this work presents a viable strategy to convert industrial flue gas into valuable microalgal products, enabling sustainable and profitable carbon utilization.