Carbon Sequestration and Pollution Reduction Mechanisms of <i>Chlorella</i> sp. for Simulated Flue Gas

Nitric oxide (NO), a signaling molecule and free radical, regulates microalgal photosynthesis, yet its potential in enhancing carbon fixation alongside pollutant mitigation remains underexplored. This study investigated the effects of NO (0, 50, 100 ppm) in simulated flue gas (15% CO₂) on <i>Chlorella</i> sp., examining intracellular/extracellular NO dynamics, antioxidant response, key enzyme activity (nitrate reductase), and growth-photosynthesis coupling. Under optimized aeration (25 mL min^-1, 3 h), 50 ppm of NO optimally elevated intracellular (0.62-1.30 nmol L^-1) and extracellular (2.56-3.90 nmol L^-1) NO levels, mitigating oxidative stress while stimulating nitrate reductase activity. This concentration maximally promoted cell proliferation (152.7% increase in algal density) and photosynthetic quantum yield (9.7% higher <i>Fv</i>/<i>Fm</i>). Consequently, the CO₂ removal rate increased by approximately 43%, coupled with a NO removal efficiency of 33.1%. These findings suggest that, under controlled experimental conditions that exclude SO₂ and other components of real flue gas, moderate supplementation of NO can enhance microalgal carbon fixation and reduce nitrogen oxide emissions by improving photosynthetic efficiency and biomass accumulation. This presents a promising strategy for integrated flue gas bioremediation.