BACKGROUNDSemi-continuous microalgae cultivations are large-scale production alternatives that maintain high microorganism growth rates. Studies show that semi-continuous cultivation can be conducted in two ways. In one, a blend concentration is set for the linear phase. The other uses a time interval dilution. This present work aimed to determine which mode of semi-continuous cultivation of Spirulina sp. LEB 18 presented the best kinetic response. RESULTSFor the Spirulina sp. LEB 18 cultivation, the blend concentration was 1.6 g L-1. The maximum average productivity (0.092 g L-1 d(-1)) and biomass amount (8.37 g) were found for the assay with blend concentration of 1.6 g L-1 and a renewal rate of 40% (v/v). CONCLUSIONThe best semi-continuous cultivation mode for Spirulina sp. LEB 18 used a fixed blend concentration. This work proved the importance of setting a blend concentration on a theoretical biochemical and biotechnological basis. (c) 2015 Society of Chemical Industry