Macro assessment of microalgae-based CO2 sequestration: Environmental and energy effects

Abstract

Microalgae are the most important types of bioenergy-producing and environmentally friendly media used in carbon sequestration, but the macro performance in carbon emission reduction has not yet been understood accurately. To assess the performance and the enviro-energy effect of microalgae-based CO2 sequestration, a comprehensive quadric surface-based logistic model was proposed to characterize the specific production rate of microalgae cultivated under varying key physicochemical factors, including input CO2 concentration, N-source concentration, P-source concentration, light intensity, and culture temperature. The effects of these factors were addressed based on the proposed model. The results indicate that the quadric surface-based logistic model predicts the specific production rate more accurately and effectively (R2 = 0.9509) than the conventional multi-factors Monod-Droop model. It enhances the generalization performance by including more influencing factors, considering the independent and interactive effects, and avoiding the possibility of negative values that occur in regular response surface methodology. Furthermore, the performances of microalgal-biomass yields and CO2 sequestration were determined. It is suggested that, theoretically, a maximum of 2.35 GtCO2 can be sequestrated in 100,000 km2 culture area, accounting for 8.01–5.31% of global CO2 emission reductions in 2020. On average, annual 0.5393 GtCO2 sequestration and 324.33 million tons of microalgal-biomass yields would be benefited when using 53,000 km2 culture area, even though the high economic performance for the microalgal-diesel conversion is challenging to achieve. Microalgae show a great potential in environmentally friendly CO2 mitigation by converting both atmospheric and industrial CO2 into biomass and bioenergy.