Assessing the impact of CO₂ concentration on growth, biomass productivity, and CO₂ fixation rate in a mixed Scenedesmus culture

Abstract

The CO2 accumulation in the atmosphere requires sustainable biotechnological mitigation strategies, such as biofixation by microalgae. This study evaluated the effect of CO2 concentration (0% - 20% v/v) on the growth parameters, biomass productivity, and CO2 fixation efficiency of a Scenedesmus consortium (S. quadricauda, S. obliquus, and S. dimorphus). The cultures were carried out in a bubble column photobioreactor, and growth parameters were determined by fitting the experimental data to the Gompertz model (R² ≥ 0.988). The results showed that the highest stationary phase biomass concentration (????∞) was achieved at 15% CO2 (0.650 g L⁻¹), whereas the highest specific growth rate (μ = 0.548 d⁻¹) was observed in the control without added CO2. The maximum biomass productivity (0.054 g L⁻¹ d⁻¹) and CO2 fixation rate (0.102 g L⁻¹ d⁻¹) occurred within the range of 10%–15% CO2. The carbon balance indicated that the overall CO2 capture efficiency was low, reaching a maximum of 0.131% at 10% CO2. The results indicate that the principal limitation is not biological tolerance, but mass transfer. Therefore, optimizing the system configuration is essential to develop efficient phototrophic technologies for biological CO2 capture.