A microalgal-based approach to carbon capture and reuse: impacts of varying culture conditions on Scenedesmus acutus productivity and biochemical composition

Warner, Mark E.Stewart, JenniferVarious mitigation systems have been proposed to reduce point-source emissions of carbon dioxide. Microalgae-based carbon capture and reuse capitalizes on the organisms’ natural ability to biologically fix carbon and accumulate metabolites in high quantities that could make the entire process profitable. In order further optimize the freshwater chlorophyte Scenedesmus acutus (S. acutus) for carbon capture at a coal-fired power plant, laboratory studies were conducted to investigate the influence of flue gas, switching from flue gas to bicarbonate supplementation, and nitrogen source on the growth and biochemical composition of the alga. A survey using next generation DNA sequencing was also conducted to identify invading organisms that potentially cause the death of S. acutus in a pilot-scale photobioreactor at the demonstration facility in Boone County, Kentucky. Results showed that the high CO2 concentration was responsible for the increased productivity in cultures exposed to simulated flue gas, despite a considerable decrease in pH. Protein content was also enhanced in these cultures, which is promising as a future application of S. acutus is to make plastic from the protein-containing fraction. Sodium bicarbonate supplementation proved to be an appropriate option to maintain the health and biochemical composition of the algae in the event of a power outage. Using urea as a nitrogen source is more cost-effective than sodium nitrate, and it supported greater productivity and protein content in S. acutus cultures grown under air, 9% CO2, and simulated flue gas. Lastly, several contaminants, including other chlorophyte microalgae, and parasitic fungi, as well as two potential sources of contamination were identified in the outdoor cultivation of S. acutus growing on flue gas in a closed photobioreactor system. These results indicated that S. acutus is a good candidate for carbon capture and reuse at a coal-fired power plant and highlighted directions of future study to continue optimization of this alga.University of Delaware, School of Marine Science and PolicyM.S