Impact of Nitrogen Species on Algal Carbon Capture

Author

Lauren J. Todd, Clemson UniversityFollow

Date of Award

8-2024

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biosystems Engineering

Committee Chair/Advisor

Caye Drapcho

Committee Member

Mary Katherine Watson

Committee Member

Yu-Bo Wang

Committee Member

Tom Owino

Abstract

Increasing global carbon emissions from fossil fuel combustion and the resulting detrimental effects of climate change have created a need for atmospheric carbon drawdown. Biological-based carbon capture not only sequesters carbon dioxide (CO₂) but also provides a sustainable source of biomass for biofuels and biomaterials. Thus, the aim of this research was to examine freshwater green algal growth with total ammoniacal nitrogen (TAN) and nitrate nitrogen (NO₃-N) sources at high pH for improving carbon capture potential. The following objectives were accomplished: nitrogen uptake was identified as simultaneous or sequential, the effect of TAN and NO₃-N on culture pH was quantified, and kinetic and stoichiometric growth parameters were examined for the two nitrogen sources.

The literature review discusses the impact of TAN and NO₃-N on algal growth and culture pH, in which autotrophic algal growth using TAN lowers culture pH by producing H⁺ ions, and NO₃-N raises pH by consuming H⁺. The Monod model kinetic constants from microalgal growth studies are summarized for each nitrogen source, and inhibitory levels of TAN are compiled. The properties of carbonate equilibrium reactions with passive CO­₂ diffusion, enhanced CO₂ diffusion in alkaline systems, and subsequent inorganic carbon-limited algal growth are presented to justify a high culture pH design.

Scenedesmus sp. growth was observed in open reactors with various TAN and NO₃-N treatment ratios. Specific growth rates were analyzed based on three identified phases of growth based on nitrogen and carbon substrate utilization. The highest specific growth rates were observed during phase one with TAN utilization and peak observed carbon, with an average of 0.043 hr^-1 that was not impacted by initial TAN. Biomass yields on a nitrogen basis were assessed based on periods of TAN or NO₃-N use. In reactors containing both nitrogen sources, TAN was utilized preferentially by the algae with NO₃-N utilization after TAN depletion. The culture pH was stable during TAN consumption and rose once NO₃-N was used; the peak pH for the largest TAN:NO₃-N ratio was 10.990, while the peak pH for the NO₃-N only treatment was 11.319. The results of this study can aid the design of algal cultivation systems for carbon capture, specifically the application of NO₃-N and TAN as a biological pH control method to optimize both carbon capture and algal growth.

Recommended Citation

Todd, Lauren J., "Impact of Nitrogen Species on Algal Carbon Capture" (2024). All Theses. 4379.
https://open.clemson.edu/all_theses/4379