Application of a microalga, Tetradesmus obliquus PF3, for NO and CO₂ removal from actual flue gas via cultivating in wastewater

Greenhouse gas (GHG) emissions, particularly anthropogenic emissions, are the primary drivers of climate change. The cultivation of microalgae represents a highly promising strategy for mitigating atmospheric GHG levels. The growth characteristics and GHG mitigation capabilities of Tetradesmus obliquus PF3 were investigated in domestic wastewater at a thermal power plant. The maximum cell density and productivity were 1.52 ± 0.01 g L⁻¹ and 0.33 ± 0.01 g L⁻¹ day⁻¹, respectively. Utilizing a serial configuration of two reactors, the elimination efficiency of NO and CO₂ attained values of 78 ± 4% and 14 ± 4%, respectively. NO concentration at the outlet was less than 24.6 ± 2.9 mg m⁻³, meeting the latest Chinese discharge limits. Besides, the recovery efficiency of NO and CO₂ increased to 77 ± 8% and 2.24 ± 0.04%, respectively, compared to that of the single reactor (40 ± 3%, 0.9 ± 0.0%). A removal efficiency of over 90% was achieved for TN and TP in domestic wastewater. The concentrations of COD (76.5 mg L⁻¹), NH₄⁺-N (0.9 mg L⁻¹), TN(6.31 mg L⁻¹), and TP (0.35 mg L⁻¹) in effluent were below the thresholds of 100 mg L⁻¹, 25 mg L⁻¹, none data, and 3 mg L⁻¹, respectively, complying with the Chinese Discharge Standard (Class II criteria set forth) for Municipal Wastewater Treatment Plants Pollutants. The harvested biomass exhibited a high content of carbohydrates and proteins, making it a viable feedstock for biofuels and bio-fertilizers. Our results demonstrate that Tetradesmus obliquus PF3–based flue gas treatment technology can simultaneously realize GHG removal, wastewater bio-remediation, and biomass recovery.