a b s t r a c tIn this study, we evaluated the effect of growing Dunaliella tertiolecta microalgae using CO 2 from brewing on the production of lipid and carotenoid-rich biomass. An integrated system of microalgae photobioreactors and yeast fermenters was used, thus providing biological CO 2 continuously to the microalgae culture. Yeast cultures were first carried out in fermenters using synthetic medium. With a step-wise increasing glucose concentration from 10 to 60 g L −1 , the CO 2 that came from 24 h yeast cultivation gave the highest biomass formation, carotenoids and lipid contents, and productivities by the microalgae. Reproduction of these experiments using beer fermentation instead of synthetic medium was carried out using different volumes of wort coupled to microalgae cultivations. The values obtained for microalgae cultures when using CO 2 from beer fermentation were 1.10 ± 0.05 g L −1 of biomass, 0.18 ± 0.01 g L −1 day −1 of biomass productivity, 0.58 ± 0.06 day −1 specific growth rate, 4.74 ± 0.59 mg g −1 of carotenoids per biomass dry weight, 0.86 ± 0.06 mg L −1 day −1 of carotenoids productivity, and 135 ± 4 mg g −1 of lipids. These values are almost twice as high as the values observed for control cultivations in which atmospheric CO 2 was used, showing that the integration system of yeast fermenters and microalgae photobioreactors is an interesting alternative to improve biomass formation and product contents. All D. tertiolecta cultures showed the same carotenoids profile, being lutein the major carotenoid (46.7 ± 2.0% of total carotenoids).
RESUMO-Microalgas são organismos unicelulares com a capacidade de transformar gás carbônico e luz em matéria orgânica como pigmentos e lipídeos. Dentre os macronutrientes necessários para o crescimento das microalgas, está o nitrato, o qual está diretamente associado à produção de biomassa e de lipídeos. Neste trabalho foi estudado o efeito da adição de NaNO 3 em etapas no cultivo da microalga Chlorella sp. Os cultivos foram realizados em fotobiorreatores de placa tipo airlift, tendo como meio de cultivo base Guillard f/2, com uma quantidade predefinida de 300 mg L-1 de NaNO 3 , adicionados em etapas (1 x 300, 2 x 150, 3 x 100 ou 5 x 60). A maior concentração de biomassa final foi obtida na adição em três etapas (1,86 g L-1) e o maior conteúdo de lipídeos na biomassa seca foi obtido adição de NaNO 3 em uma etapa (6,02 %). A produtividade de lipídeos, porém, foi maior no experimento em que a adição de NaNO 3 ocorreu em duas etapas (10,9 mg L-1 d-1).
Mathematical models are presented to describe the relationship between nitrogen consumption, biomass growth, and carotenoid production by the microalgae Dunaliella tertiolecta BE 003 grown under nitrogen-limited and nonlimited conditions. The nitrogen uptake was modeled by an n-order nitrogen-catalyzed reaction. Three different expressions were proposed for the biomass-specific growth rate. Carotenoid production was fitted using the Luedeking-Piret equation. The nitrogen-catalyzed expression proved to be adequate to model nitrogen uptake by D. tertiolecta over a wide range of nitrogen concentrations. Biomass expression must be improved to describe the cessation of growth when nitrogen is still available in the cultures. The Luedeking-Piret expression successfully modeled the carotenoid production.
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