Optimization of the repeated batch cultivation of microalga Spirulina platensis in open raceway ponds

The cyanobacterium Spirulina platensis is extensively used in human nutrition because it is a source of beneficial phenolics, proteins, unsaturated lipids and vitamins. Repeated batch cultivation of photosynthetic microorganisms is widely used industrially because it allows actively growing cultures to be maintained for long periods of time. Despite this, there have been few detailed studies involving the repeated batch cultivation of S. platensis. We used a Box–Behnken factorial design to optimize the repeated batch cultivation of S. platensis in open raceway ponds at 30 °C under a light intensity of 3000 lx and a 12 h photoperiod for a total cultivation time of 1500 h (60 days) where the variables were blend concentration (0.40, 0.60 and 0.80 g l− 1), renewal rate (20, 40 and 60%) and culture medium, the culture media being Zarrouk medium in three different dilutions. We found that S. platensis productivity was 0.028 to 0.046 g l− 1 day− 1 and the maximum specific growth rate (μmax) 0.038 to 0.138 day− 1, all the process variables being statistically significant at p < 0.05. Our results show that semicontinuous cultivation of S. platensis can be optimized using a medium consisting of 20% (v/v) Zarrouk Medium, a S. platensis blend concentration of 0.40 g l− 1 and a renewal rate of between 40 and 60%.