Toward Carbon Neutrality: The Modeling and Implementation of an Algal Carbon Capture System

Carbon dioxide (CO2) emissions from anthropogenic sources are causing widespread ecological disruptions. The uptake of CO2 by aquatic photoautotrophs is one strategy for carbon capture to mitigate these emissions. The objectives of this thesis were to investigate carbonate chemistry and algal growth equations to improve MATLAB model predictive capability in a closed-reactor system and to develop, design, and evaluate a non-fossil fuel technology and strategy for operation of the Algal Carbon Capture System (ACCS). A dynamic growth model based on carbon-limited algal specific growth rate with Monod kinetics, considering CO2, bicarbonate (HCO3), and carbonate (CO32-) as substitutable substrates, provided the best estimates for algal biomass in closed-reactors. Total inorganic carbon (TIC), CO2, HCO3-, CO32-, pH, and alkalinity were also well predicted. This model improves upon those reviewed by incorporating kinetic rates of inorganic carbon species interconversion instead of the equilibrium assumption. Discrepancies in rate constants of the bicarbonate hydroxylation reaction indicate more exploration of these parameters is needed. Here is proposed the use of the geometric mean (2.25 108 M-1∙s-1) for the forward rate constant. Underprediction of algal biomass and improved response of CO2/HCO3-/CO32- substitutable model over the CO2/HCO3- substitutable may indicate an unknown biological pathway for the use of carbonate for growth. An airlift pump prototype was designed, built, implemented, and tested at the ACCS to create water flow in one raceway channel as a demonstration of the concept. The airlift operates solely on available solar power and provides at its outlet a water velocity of 12.5 cm/s, and an average channel velocity of 1.02 ± 0.15 cm/s as the surface kinetic energy is distributed throughout the channel depth