Treatment of Nitrogen Oxides by Chlorella vulgaris Algae in Photobioreactors

Author

Steven Shihady, California Polytechnic State University, San Luis ObispoFollow

DOI: https://doi.org/10.15368/theses.2014.136
Available at: https://digitalcommons.calpoly.edu/theses/1284

Date of Award

8-2014

Degree Name

MS in Civil and Environmental Engineering

Department/Program

Civil and Environmental Engineering

Advisor

Yarrow Nelson

Abstract

The effectiveness of algae to treat NO₂and NO in simulated flue gas was tested using Chlorella vulgaris in photobioreactors (PBRs) using NO_xconcentrations between 30 ppm to 780 ppm. NO_xdissolved and reacted in water to form NO₃^-and NO₂^-in the PBR growth medium, providing a nitrogen source that the algae readily assimilated for cell synthesis. Three 20-L photobioreactors were inoculated with a pure culture of C. vulgaris prepared in Bristol growth medium and algae were grown in the PBRs at 25°C and pH of 7.0 in a modified Bristol medium that did not contain nitrogen compounds. The C. vulgaris grew substantially using NO₃^-/NO₂^-as its nitrogen source for cell synthesis. The NO₃^-and NO₂^-were formed through the dissolution and oxidation/reduction of NO_xfrom the simulated flue gas. Algal growth by assimilation of NO₃^-and/or NO₂^-allowed for continual dissolution of NO_x, resulting in NO_xremoval rates from the gas phase of up to 97%, with residual nitrogen of up to 7 mg-N/L in solution. Algae grew from an initial cell density of 3.1 x 10⁵cells/L to cell densities of up to 1.85 x 10⁷cells/mL and dry weights of up to 243 mg/L. Cell nitrogen content varied from 4-8%. PBR to treatment of gaseous NO_xwas analyzed in terms of mass transfer rates, chemical kinetics, and biological growth.