Development of an optimal light-feeding strategy coupled with semi-continuous reactor operation for simultaneous improvement of microalgal photosynthetic efficiency, lutein production and CO2 sequestration

• Incremental illumination reduced light-induced stress that influences lutein synthesis.
• Linear light-feeding mode drastically enhanced both lutein productivity and content.
• Optimal illumination strategy was integrated with semi-continuous reactor operation.
• Integrated semi-continuous mode improved photosynthetic efficiency and lutein production .

In addition to leveraging some environmental and energy benefits, microalgae can also be used as a potentially sustainable source for carotenoids like lutein for healthcare applications. As light influences biosynthesis of lutein in microalgae, it would be interesting to investigate the role of incremental illumination in enhancing photosynthetic efficiency and consequent lutein production, while sequestering CO2 simultaneously. Thus, in this study, an optimal light feeding strategy coupled with a semi-continuous reactor operation was developed for achieving the above-mentioned goals. At a light intensity of 260 μmol m−2 s−1 as optimized in batch mode, baseline lutein productivity of 4.32 mg L−1 d−1 was obtained, when culturing Chlorella minutissima under optimal process conditions. On switching over to incremental illumination modes, the linear light-feeding (Strategy-III) resulted in higher lutein productivity of 5.35 mg L−1 d−1 with photosynthetic efficiency of 8.38%. When Strategy-III was integrated with semi-continuous mode involving 20% medium replenishment, lutein productivity, photosynthetic efficiency and CO2 sequestration rate were further enhanced by 19%, 41% and 34% respectively. Moreover, on this process optimization and integration, light-energy consumption was significantly reduced by 32%, in comparison with constant-illumination. Thus, this optimal production strategy resulted in significantly higher lutein productivity, content and photosynthetic efficiency, as compared to the relevant studies reported in literature.