Carbon dioxide from geothermal gas converted to biomass by cultivating coccoid cyanobacteria
2018
The Blue Lagoon is a geothermal aquifer with a diverse ecosystem located within the Reykjanes UNESCO Global Geopark on Iceland’s Reykjanes Peninsula. Blue Lagoon Ltd., which exploits the aquifer, isolated a strain of coccoid cyanobacteria Cyanobacterium aponinum (C. aponinum) from the geothermal fluid of the Blue Lagoon more than two decades ago. Since then Blue Lagoon Ltd. has cultivated it in a photobioreactor, for use as an active ingredient in its skin care products. Until recently, the cultivation of C. aponinum was achieved by feeding it on 99.99% (4N) bottled carbon dioxide (CO₂). In this investigation, C. aponinum was cultivated using unmodified, non-condensable geothermal gas (geogas) emitted from a nearby geothermal powerplant as the feed-gas instead of the 4N-gas. The geogas contains roughly 90% vol CO₂ and 2% vol hydrogen sulfide (H₂S). A comparison of both CO₂ sources was made. It was observed that the use of geogas did enhance the conversion efficiency. A 13 weeks’ average CO₂ conversion efficiency of C. aponinum was 43% and 31% when fed on geogas and 4N-gas, respectively. Despite the high H₂S concentration in the geogas, sulfur accumulation in the cultivated biomass was similar for both gas sources. Our results provide a model of a CO₂ sequestration by photosynthetic conversion of otherwise unused geothermal emission gas into biomass.
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