Biological and chemical carbon sequestration of microalga Scenedesmus obliquus HTB1 under high light and elevated CO2

Microalga Scenedesmus obliquus, has been known to thrive in high concentrations of CO 2 and is considered a promising strain for algal-based carbon capture technology. In this study, we aim to maximize the carbon capture capacity of our isolate, Scenedesmus obliquus HTB1, by optimizing its photosynthetic efficiency and biomass productivity, and promoting chemical precipitation of CaCO 3 through increased pH in the algal system. While HTB1 has been considered a promising alga for carbon sequestration, its capacity to grow under high light has not been tested. We found that with 10% CO 2 and high light, HTB1 can achieve a growth rate of 0.503 g/L/day. Interestingly, under these conditions, HTB1 maintained higher photosynthetic efficiency than it did under high light and ambient air treatment. This result suggests that with 10% CO 2 , HTB1 cells adapt well to high light exposure, allowing for fast growth and high biomass density. Upon reaching dense biomass, the supplement of 10% CO 2 was stopped, increasing the pH to 10.67. Calcium chloride was added, yielding 1.35 g/L CaCO 3 precipitate. Our results show that treatment with 10% CO 2 promotes the growth of HTB1 and increases the culture alkalinity thereof, yielding nearly double the calcium carbonate precipitate produced by cultures supplied with ambient air. Based on these data, we estimated that biological carbon sequestration can remove 0.702 g CO 2 /L/day, while chemical carbon sequestration can remove 0.593 g CO 2 /L based on calcium carbonate precipitate yield. Together, biological and chemical carbon capture by HTB1 provide a promising system for CO 2 mitigation from point sources. • We assessed the biological and chemical carbon capture capacity of a novel strain of Scenedesmus obliquus (HTB1). • Microalgal calcium carbonate precipitation (MAICP) was induced at the conclusion of a robust growth experiment, producing 1.37 g/L of calcium carbonate. • A maximum dry biomass of over 6 g was achieved through growth with 10% CO 2. • Our strain is highly productive under both elevated CO 2 and high light (400 umol). • We demonstrate our strain as a strong candidate for point-source carbon capture from flue gas emissions.