A symbiotic gas exchange between bioreactors enhances microalgal biomass and lipid productivities: taking advantage of complementary nutritional modes |
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Authors: | C A Santos M E Ferreira T Lopes da Silva L Gouveia J M Novais A Reis |
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Institution: | 1.LNEG, U. Bioenergia, edificio F,Lisbon,Portugal;2.Institute for Biotechnology and Bioengineering, Instituto Superior Técnico,Lisbon,Portugal |
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Abstract: | This paper describes the association of two bioreactors: one photoautotrophic and the other heterotrophic, connected by the
gas phase and allowing an exchange of O2 and CO2 gases between them, benefiting from a symbiotic effect. The association of two bioreactors was proposed with the aim of improving
the microalgae oil productivity for biodiesel production. The outlet gas flow from the autotrophic (O2 enriched) bioreactor was used as the inlet gas flow for the heterotrophic bioreactor. In parallel, the outlet gas flow from
another heterotrophic (CO2 enriched) bioreactor was used as the inlet gas flow for the autotrophic bioreactor. Aside from using the air supplied from
the auto- and hetero-trophic bioreactors as controls, one mixotrophic bioreactor was also studied and used as a model, for
its claimed advantage of CO2 and organic carbon being simultaneously assimilated. The microalga Chlorella protothecoides was chosen as a model due to its ability to grow under different nutritional modes (auto, hetero, and mixotrophic), and its
ability to attain a high biomass productivity and lipid content, suitable for biodiesel production. The comparison between
heterotrophic, autotrophic, and mixotrophic Chlorella protothecoides growth for lipid production revealed that heterotrophic growth achieved the highest biomass productivity and lipid content
(>22%), and furthermore showed that these lipids had the most suitable fatty acid profile in order to produce high quality
biodiesel. Both associations showed a higher biomass productivity (10–20%), when comparing the two separately operated bioreactors
(controls) which occurred on the fourth day. A more remarkable result would have been seen if in actuality the two bioreactors
had been inter-connected in a closed loop. The biomass productivity gain would have been 30% and the lipid productivity gain
would have been 100%, as seen by comparing the productivities of the symbiotic assemblage with the sum of the two bioreactors
operating separately (controls). These results show an advantage of the symbiotic bioreactors association towards a cost-effective
microalgal biodiesel production. |
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