Growth and Modeling of Freshwater Algae as a Function of Media Inorganic Carbon Content

In response to global climate change, the Department of Energy (DOE) has specified advanced biological processes, such as cultivation of algal biomass in alkaline ponds, as part of a carbon management plan. The goal of this thesis was to investigate use of a mixed freshwater algal culture for biological carbon mitigation. Extensive review of carbonate dynamics, laboratory investigations to characterize algal growth, and development of a dynamic algal growth model were completed. The presented literature review summarizes carbonate equilibria and kinetics needed for development of carbon mitigation technologies, especially in freshwaters. Reaction mechanisms, equilibrium relationships, kinetic rate constants, and kinetic rate laws are used to develop mass balance equations (MBEs) for species concentrations in closed systems. Several strategies for quantifying reaction-enhanced CO2 transport are presented to develop carbonate species MBEs for open systems. Batch algal growth was analyzed in closed and open batch reactors. Specific growth rates, biomass production, and peak pH generally increase with increasing initial TIC concentration in closed and open reactors. Closed algal cultures kinetically responded to CO2, HCO3-, and CO3\u3c2- concentrations (μmax = 0.0726 hr-1, KCO2 = 4.47 × 10-8, KHCO3 = 5.70 × 10-4, KCO3 = 8.70 × 10-4), which suggests employment of carbon concentrating mechanisms (CCMs). Analysis of batch growth in open reactors revealed that carbon sequestered per supplied TIC exponentially (R2 = 0.9717) decreased with increasing initial TIC. Dynamic mathematical models aimed at predicting algal biomass and carbonate species concentrations in closed and open batch reactors were developed. The CO2/HCO3-/CO32- substitutable substrates Monod equation for predicting TIC-limited algal specific growth rates best estimated biomass concentrations in closed and open batch reactors. However, inaccuracies were observed for some water chemistry parameters. The closed batch reactor model was calibrated based on photosynthetic oxygen production and verified using data from laboratory investigations. A sensitivity analysis for the open batch reactor model suggests that photosynthetic oxygen production and biomass light attenuation coefficients should be further investigated to improve open algal growth model simulations