Microalgal Bioremediation of Firewood-based Flue Gas for CO2 Fixation

Abstract

Flue gas (FG) contains significant levels of gaseous pollutants that must be effectively managed to prevent air pollution and global warming. The primary components of FG include carbon dioxide, carbon monoxide, sulfur oxides, nitrogen oxides, and trace metals. These pollutants are often removed using physico-chemical methods, which generally incur higher costs. An emerging technique for treating FG involves using microalgae, which have shown promise for efficiently removing and sequestering CO2, SOx, and NOx from FG, while also producing commercially valuable by-products. In the present study, a novel microalgal strain was evaluated for its CO₂ fixation potential and lipid accumulation capability under flue gas conditions. The isolate was identified as Nephrocytium agardhianum sp., belonging to class Chlorophyceae. Various physicochemical parameters and growth kinetics, including CO₂ fixation rate, biomass yield, lipid content, and pH, were investigated. The biomass yield reached 3.73 g L-1 under 6% CO₂ supplementation and 3.53 g L-1 under 100% FG supplementation. Although the biomass yields were comparable, lipid accumulation was higher in FG-supplemented reactors (24%) than in reactors supplied with 6% CO₂ (18%). The CO₂ fixation rate was similar in both study conditions, however, the specific growth rate was higher in FG-supplemented reactors. These findings demonstrate that the novel strain can tolerate toxic flue gas containing 6% CO₂ while maintaining high lipid productivity. The lipid-rich biomass generated under flue gas conditions highlights the potential of N. agardhianum as a feedstock for subsequent biofuel production, thereby linking biological CO₂ mitigation with renewable bioenergy generation. Further studies are required to evaluate its tolerance to higher CO₂ concentrations and to scale up the process for efficient large-scale FG bioremediation.