Enhanced carbon utilization efficiency and FAME production of Chlorella sp. HS2 through combined supplementation of bicarbonate and carbon dioxide

Abstract

The optimum concentration of dissolved carbon in the microalgal culture medium is a vital requirement for enhanced biomass production. The present study investigates the effect of supplying NaHCO3 with CO2 as the inorganic carbon source to enhance the utilization efficiency of CO2 for maximum FAME productivity of Chlorella sp. HS2. The specific growth rate (0.615 d−1), biomass productivity (530.1 mg L−1 d−1), CO2 biofixation rate (996.4 mg L−1 d−1), FAME productivity (141.8 mg L−1 d−1) and FAME content (26.76%) were found to be maximized at NaHCO3 concentration of 0.5 g L−1 with 1% (v/v) CO2 enriched air (0.25 vvm flow rate) supplementation in shake flask condition. The FAME productivity (169.37 mg L−1 d−1) and FAME content (31.2%) were 1.19 and 1.16 times higher respectively in the flat panel photobioreactor than in shake flask condition. Fatty acid profile and biofuel properties show suitability for biodiesel production. The economic assessment revealed that combining supplementation of both carbon sources greatly reduces the carbon supply costs, from $8.92 Kg−1 when only NaHCO3 was used as the carbon source down to $0.86 Kg−1 when 1% CO2 was supplied alongside NaHCO3. These findings show that combined application of NaHCO3 and CO2 is the more cost-effective approach of supplying carbon source to microalgae for FAME production.