Evaluation of photosynthetic efficacy and CO2 removal of microalgae grown in an enriched bicarbonate medium

Abstract

Bicarbonate species in the aqueous phase is the primary source for CO₂ for the growth of microalgae. The potential of carbon dioxide (CO₂) fixation by Chlorella pyrenoidosa in enriched bicarbonate medium was evaluated. In the present study, effects of parameters such as pH, sodium bicarbonate concentration and inoculum size were assessed for the removal of CO₂ by C. pyrenoidosa under mixotrophic condition. Central composite design tool from response surface methodology was used to validate statistical methods in order to study the influence of these parameters. The obtained results reveal that the maximum removal of CO₂ was attained at pH 8 with sodium bicarbonate concentration of 3.33 g/l, and inoculum size of 30 %. The experimental results were statistically significant with R ² value of 0.9527 and 0.960 for CO₂ removal and accumulation of chlorophyll content, respectively. Among the various interactions, interactive effects between the parameters pH and inoculum size was statistically significant (P < 0.05) for CO₂ removal and chlorophyll accumulation. Based on the studies, the application of C. pyrenoidosa as a potential source for carbon dioxide removal at alkaline pH from bicarbonate source is highlighted.

Keywords: Carbon concentrating mechanism; Chlorella pyrenoidosa; Dissolved inorganic carbon; Mixotrophic condition; Response surface methodology.

Fig. 1

Flow chart representation of response surface methodology

Fig. 2

Growth profile of microalgae under optimized condition [pH 8, NaHCO₃ 3.33 (g/l), inoculum size −30 (%)] and experimental condition

Fig. 3

Surface plot for CO₂ removal (%). a Conc. of NaHCO₃ (g/l), pH. b Inoculum size (%), pH. c Inoculum size (%), Conc. of NaHCO₃ (g/l)

Fig. 4

Surface plot for chlorophyll (mg/l). a Conc. of NaHCO₃ (g/l), pH. b Inoculum size (%), pH. c Inoculum size (%), Conc. of NaHCO₃ (g/l)