Mass transfer characteristics and effect of flue gas used in microalgae culture

Flue gas not only contains carbon dioxide (CO₂) but also air pollutants (sulfur oxides (SO_x) and nitrogen oxides (NO_x)). The effective utilization of flue gas could help us to reduce the cost of microalgal biomass production. This study assessed and explored the utilization of flue gas for the absorption characteristics of different components and their biological effect in microalgal culture systems. In abiotic absorption experiments, the absorptivity of CO₂ was reduced by a maximum of 3.1%, and the concentration of the available carbon source in the culture medium was decreased by 6.7% when sulfur dioxide (SO₂, at 100 mg/m³) was presented in the flue gas. Meanwhile, the presence of oxygen (O₂, at 4%) in the flue gas improved the absorptivity of nitric oxide (NO). When Scenedesmus dimorphus was cultured using bisulfites and nitrites (at 10 mmol/L and 8 mmol/L, respectively) as the sulfur and nitrogen sources, SO_x and NO_x in the flue gas did not significantly affect growth of microalgal cells and the carbohydrate, lipid, and protein content. The consumption rates of nutrient elements were calculated, which could provide an adjustment strategy for the initial gas source when culturing microalgae with the flue gas. This study indicates that the flue gas used for microalgal culture should be partially desulfurized, so that the SO_x and CO₂ concentrations can optimize growth of microalgal cells, while the denitrification might not be needed since the flue gas can be oxidized to utilize the NO. KEY POINTS: • The concentration of the available carbon source in the culture medium was decreased when SO₂ was presented in the flue gas, and the presence of O₂ in the flue gas improved the absorptivity of NO. • An adjustment strategy for the initial gas source when culturing microalgae with the flue gas was firstly proposed. • For flue gas containing 10% CO₂ and 60 mg/m³ of SO₂, growth of Scenedesmus dimorphus showed no difference in cell growth in normal culture conditions.