Promotion of Cyanobacteria Growth Induced by Fine Bubble Injection

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  • ファインバブルの導入によるシアノバクテリアの増殖促進

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Abstract

In this study, a cultivation technique enabling growth promotion of cyanobacteria with low efficiency CO2 absorption and conversion to organic compounds was developed utilizing the gas-liquid interfaces surrounding fine air bubbles as new reaction fields for photosynthesis. Cyanobacteria CO2 absorption efficiency is increased in the regions near the fine bubble surfaces because of the accelerated CO2 mass transfer caused by minimizing the bubble diameter, as well as cyanobacteria accumulation due to the negative charge on the fine bubble surface; hence, the rate of photosynthesis is increased and cyanobacteria growth is promoted. Fine air bubbles with an average bubble diameter （dbbl） of 80 μm were continuously supplied to culture medium containing cyanobacteria in a semi-batch photobioreactor equipped with a self-supporting bubble generator, a fluorescent lamp, and a reaction vessel and the cyanobacteria were grown at a reaction temperature of 30 ℃. The light intensity was changed by the number of fluorescent lamps located inside and outside of the reaction vessel. Additionally, the dbbl was varied along a range of 40 to 6,000 μm at a constant light intensity. Consequently, when the light intensity range was 37 - 527 μmol·m－2·s－1 at a dbbl of 80 μm, the specific growth rate of the cyanobacteria （rsg） showed a maximum value at a light intensity of 365 μmol·m－2·s－1. Furthermore, at a light intensity of 365 μmol·m－2·s－1, the rsg noticeably increased with a decrease in dbbl and the rsg at a dbbl of 40 μm was approximately 2.5-fold greater than that at 1,500 μm. These results indicate that fine bubble injection promoted cyanobacteria growth in a semi-batch photobioreactor under CO2-limited conditions.

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