Mixotrophic cultivation of microalga Spirulina platensis using molasses as organic substrate

Spirulina is a microalga rich in proteins, vitamins and polyunsaturated fatty acids. This microorganism grows photosynthetically but an organic substrate can stimulate its growth. Molasses is a by-product from sugar industry, containing more than 50% of sugar, and potentially useful as substrate to microalgae culture. On the other hand, light is needed to the photosynthetic fixation of CO2. So, we determined the effects of molasses concentration and light levels on mixotrophic biomass production by Spirulina platensis. Molasses concentration was the main factor influencing maximum biomass concentration (Xmax, g L− 1) and maximum specific growth rate (μmax, d− 1), although light intensity also influenced both parameters after 11 days. Xmax reached 2.94 g L− 1 and μmax 0.147 d− 1 while the average maximum productivity (Pmax, g L− 1 d− 1) of 0.32 g L− 1 d− 1 occurred within the first few days and was not significantly affected either by the molasses concentration or light. Biomass production was stimulated by molasses, suggesting that this industrial by-product could be used as a low-cost supplement for the growth of Spirulina platensis.