Ciência e Natura, (44), p. e52, 2022
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Commercial microalgae cultivations use the semi-continuous mode, but there are no reports of using this cultivation mode to produce carbohydrate-rich biomass. It was evaluated the biomass productivity and intracellular carbohydrates by Spirulina platensis in semi-continuous cultivation. Besides, the reuse of the culture media after the blend was accomplished in order to obtain nutrient-depleted cultures. In the first stage (Step 1), performed in closed Erlenmeyer’s flasks, it was verified that the blend concentration and renewal rate did not influence the intracellular concentration of carbohydrates. However, the interaction of variables influenced cell concentration and carbohydrates yields, being the best results obtained with blend concentration and renewal rate of 0.5 g/L and 60%, respectively. In Step 2, realized in 10 L open mini raceways, the cultures remained viable up to 3 cycles in semi-continuous mode, obtaining mean carbohydrate contents of 41.7% (w/w) and mean carbohydrate yield of 69.3 mg/L d using the media Zarrouk 30% and 70% renewal rate. These values were higher than those observed in experiments in closed bioreactors. Therefore, it was demonstrated that semi-continuous cultivation is viable to obtain biomass for bioethanol production, which represents a possibility of reusing nutrients from the culture medium itself for this purpose.