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Kinetics of Inorganic Carbon-Limited Freshwater Algal Growth at High pH

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Transactions of the ASABE. 59(6): 1633-1643. (doi: 10.13031/trans.59.11520) @2016
Authors:   Mary Katherine Watson, Caye M. Drapcho
Keywords:   Algae, Carbon management, Monod kinetics.

Abstract. Elevated atmospheric CO2 concentrations necessitate exploration of carbon management strategies to combat high CO2 emissions. Carbon sequestration, which includes capture and storage of inorganic carbon, is one potential component of a carbon management plan. In particular, utilization of atmospheric CO2 by algae has been proposed for carbon capture, particularly at high pH since CO2 absorption rates increase with increasing pH. The goal of this study was to quantify the growth and inorganic carbon utilization of a mixed freshwater green algal culture at high pH. Algal cultures were supplied with different initial media inorganic carbon concentrations (11 to 32 mg C L-1 as Na2CO3), maintained in a controlled environment, and adjusted to an initial pH of 10.3. Samples were taken daily to measure pH, alkalinity, inorganic carbon, and total suspended solids. Results indicated that the culture was dominated by at all inorganic carbon concentrations. Peak biomass, specific growth rate, and biomass carbon content generally increased with increasing initial inorganic carbon concentration. Nonlinear regression was used to estimate a maximum specific growth rate of 0.0727 h-1 and half-saturation constants of 5.36 x 10-4, 6.84, 10.4, and 17.5 mg C L-1 for CO2, HCO3-, CO32, and total inorganic carbon, respectively. Comparison of changes in the concentrations of inorganic carbon species due to pH increase and utilization by algae suggest that CO2, HCO3-, and CO32- (i.e., total inorganic carbon) contributed to biomass production. Overall, the determined stoichiometric and kinetic parameters can be used to facilitate modeling and optimization of algal-based carbon capture strategies.

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