Production of Spirulina biomass: Maintenance of monoalgal culture outdoors

The effects of sodium bicarbonate concentration, population density, and temperature on the maintenance of an outdoor monoculture of the cyanobacterium Spirulina platensis were studied. A clear response by Spirulina to the concentration of bicarbonate was evident, with 0.2 M bicarbonate representing the lowest concentration in which a monoculture could be maintained. When the temperatures fell during the winter period to some 20–25°C below the optimum for Spirulina , Chlorella sp. gradually increased and became the dominant species in the culture. Raising the temperature by covering the pond with transparent polyethylene resulted in a sharp decline in the population of Chlorella , and a gradual resumption of species dominance by Spirulina . In winter, there was an inverse relationship in the pond between the population density of Spirulina and the extent of contamination by Chlorella sp.; but no such effect was observed under field conditions at temperatures higher than 25°C.