title: A symbiotic gas exchange between bioreactors enhances microalgal biomass and lipid productivities: taking advantage of complementary nutritional modes.
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 O(2) and CO(2) 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 (O(2) enriched) bioreactor was used as the inlet gas flow for the heterotrophic bioreactor. In parallel, the outlet gas flow from another heterotrophic (CO(2) 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 CO(2) 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.
authors.affiliation: LNEG, U. Bioenergia, edificio F, Estrada do Paço do Lumiar, 22, 1649-038, Lisbon, Portugal.
authors.forename: C A
authors.initials: CA
authors.lastname: Santos
authors.forename: M E
authors.initials: ME
authors.lastname: Ferreira
authors.forename: T Lopes
authors.initials: TL
authors.lastname: da Silva
authors.forename: L
authors.initials: L
authors.lastname: Gouveia
authors.forename: J M
authors.initials: JM
authors.lastname: Novais
authors.forename: A
authors.initials: A
authors.lastname: Reis
mesh_terms: D056804:Biofuels; D018533:Biomass; D019149:Bioreactors; D001709:Biotechnology; D002245:Carbon Dioxide / Q000378:metabolism; D000460:Chlorophyta / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism; D052836:Heterotrophic Processes; D008055:Lipids / Q000096:biosynthesis*; D058086:Microalgae / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D013559:Symbiosis
chemical_list: D056804:Biofuels; D005227:Fatty Acids; D008055:Lipids; D009566:Nitrates; D002245:Carbon Dioxide; D010100:Oxygen
references.citation: Can J Biochem Physiol. 1959 Aug;37(8):911-7
references.pmid: 13671378
references.citation: Trends Biotechnol. 2008 Jul;26(7):349-50; author reply 351-2
references.pmid: 18486252
references.citation: J Microbiol Methods. 2004 Mar;56(3):331-8
references.pmid: 14967224
references.citation: Bioresour Technol. 2009 Jan;100(1):261-8
references.pmid: 18693011
references.citation: Bioresour Technol. 2002 Mar;82(1):1-4
references.pmid: 11848373
references.citation: Bioresour Technol. 2006 Apr;97(6):841-6
references.pmid: 15936938
references.citation: Biotechnol Adv. 2007 May-Jun;25(3):294-306
references.pmid: 17350212
references.citation: J Ind Microbiol Biotechnol. 2009 Feb;36(2):269-74
references.pmid: 18982369
references.citation: J Lipid Res. 1986 Jan;27(1):114-20
references.pmid: 3958609