Inorganic Carbon Supplementation to Culture Medium Enhancing Growth Performance and Pigmentation of Freshwater Microalgae Chlorella ellipsoidea

The availability of inorganic carbon in the culture media is a limiting factor for the growth of photosynthetic microalgae. However, the expense of supplying carbon dioxide to culture is a significant fraction of total energy usage. Bicarbonate salts, when added to the growth medium, can be an inexpensive inorganic carbon source for microalgae. In this study, Chlorella ellipsoidea was used to assess the capability of this species to utilize bicarbonate and determine the impact of this carbon source on growth performance and pigmentation. In a batch experiment, 0.25, 0.5, 1.0, 1.5, and 2.0 g/L of sodium bicarbonate was added to Bold's basal medium. Growth values were compared to those of the control group that received only Bold's basal medium. C. ellipsoidea was able to grow in all concentrations of bicarbonate and had a high capacity for biomass production. The exponential growth was increased with the addition of sodium bicarbonate to Bold's basal medium, and it continued on the fifteenth day of culture. Among the culture media,  Bold's basal medium with 1.5 g/L sodium bicarbonate had the highest cell density (41.17 ± 0.23 x 105 cells/mL), cell dry weight (24.55 ± 0.12 mg/L), optical density (1.33 ± 0.05), and chlorophyll a and chlorophyll b contents (6.51 ± 0.09 mg/L and 3.97 ± 0.13 mg/L, respectively). The specific growth rate significantly increased due to the addition of sodium bicarbonate up to 1.5 g/L level. The highest purity (77.04 ± 0.32 %) was found in 1.0 g/L sodium bicarbonate supplementation to Bold's basal medium followed by 73.44 ± 0.32 % purity in 1.5 g/L supplementation. The study revealed that bicarbonate can stimulate algal growth. An appropriate supply of sodium bicarbonate at 1.5 g/L to Bold's basal medium as an inorganic carbon source can be considered an acceptable alternative to carbon dioxide for the production of C. ellipsoidea.