Investigation of main factors affecting the growth rate of Spirulina

Spirulina is a kind of microalgae with high economic value, therefore, investigations of the growth of Spirulina are of great importance. In this paper, the effect of culture conditions (temperature and pH), culture medium, light source (single and combined light source) and the corresponding exposure time on the growth rate of Spirulina is extensively studied. The results showed that the optimal temperature and pH for the growth of Spirulina were 30 °C and 9.5–10.0, respectively, while the culture medium with 10 g/L of NaHCO3, 2 g/L of NaNO3, 0.6 g/L of KH2PO4, 0.2 g/L of MgSO4·7H2O and 1.2 g/L of K2SO4 achieved the best growth rate of Spirulina. When being exposed to the red light (wavelength, 620–630 nm), blue light (wavelength, 465–475 nm) and green light (wavelength, 522–532 nm), the maximum dry matter contents of Spirulina were 1.346 g/L, 1.179 g/L and 1.081 g/L, respectively, indicating that the red light was the best light source for the growth of Spirulina as a highest growth rate with an dramatic increase of 56.69% (compared to the control group) in the dry matter content was observed. 8 h were proved to be the best exposure time of red light for the growth of Spirulina within one day, where a dry matter content of 1.440 g/L was found. This was 67.64% higher than that of the control group. Combined light sources of red-blue light, red-green light and blue-green light were also applied to Spirulina, and it was found that the maximum dry matter contents of Spirulina were 1.518 g/L, 1.389 g/L and 1.232 g/L for red-blue light, red-green light and blue-green light respectively. Therefore, the Spirulina exposed to red-blue light attained the highest growth rate with the corresponding dry matter content increasing by 76.72% when compared with the control group.