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Growth Response of a Freshwater Microalga to Very High Atmospheric CO2 Concentrations
Yue, L. and Chen, W.  2005.  Isolation and determination of cultural characteristics of a new highly CO2 tolerant fresh water microalgae.  Energy Conversion and Management 46: 1868-1876.

What was done
In a search for a simple and independently useful method for removing CO2 from high-CO2-concentration stack gases, the authors isolated and cultured a freshwater microalga of the genus Chlorella that they dubbed strain ZY-1, which they then grew for periods of six days in vessels filled with growth media through which air of a variety of different CO2 concentrations was continuously bubbled.

What was learned
Maximum algal growth rates (200% greater than those observed in ambient air) were observed at 100,000 ppm CO2.  Thereafter (at higher CO2 concentrations), algal growth rates began to slowly decline.  Relative to the growth rate in bubbled ambient air, the growth rate at 200,000 ppm CO2 was 170% greater, that at 300,000 ppm was 125% greater, and that at 500,000 ppm was about 40% greater.  The authors also report that similar results have been obtained by Watanabe et al. (1992) for another Chlorella alga, by Hanagata et al. (1992) for both Chlorella and Scenedesmus species, and by Kodama et al. (1993) for the marine microalga Chlorococcum littorate.

What it means
In the words of Yue and Chen, the results of their research indicate that "the isolated ZY-1 strain can contribute to the simplification of a CO2 fixing system by microalgal cultivation," which they say has an advantage over non-biological carbon scavenging systems in that "carbon fixed by microalgae is incorporated into carbohydrates and lipids, so energy, chemicals, or foods can be produced from microalgae biomass."  On the further horizon, their research presages the potential for genetic manipulation to enable higher land plants to also become more responsive to ultra-high CO2 concentrations.

Hanagata, N., Takeuchi, T. and Fukuju, Y.  1992.  Tolerance of microalgae to high CO2 and high temperature.  Phytochemistry 31: 3345-3348.

Kodama, M., Ikemoto, H. and Miyachi, S.  1993.  A new species of highly CO2-tolerant fast growing marine microalga suitable for high density culture.  Journal of Marine Biotechnology 1: 21-25.

Watanabe, Y., Ohmura, N. and Saiki, H.  1992.  Isolation and determination of cultural characteristics of microalgae which functions under CO2 enriched atmosphere.  Energy Conversion and Management 33: 545-552.

Reviewed 24 August 2005