<p>Indoor air pollution is increasing in energy-efficient buildings with restricted natural ventilation that results in pollutant accumulation in the form of carbon dioxide (CO₂) and fine particulate matter (PM2.5). Conventional air purifiers are based on energy-consuming mechanical or chemical filtration mechanisms that are responsible for carbon emissions and maintenance. This research suggests a nature solution employing Azolla, a high-performance photosynthetic aquatic fern that grows rapidly, as a biofilter. A Computational Fluid Dynamics (CFD) model employing Navier–Stokes and advection–diffusion-reaction equations has been employed to model airflow and pollutant transport in an indoor test setup. Simulation yields the depletion of 40% of CO₂ and 55% of PM2.5 concentrations within 300&#xa0;s. These values find favorable validation with past experimental research on green plant systems, e.g., Peace Lily and green vertical walls, confirming the model. The Azolla system only uses 0.1–0.2 kWh/day, providing as much energy up to 90% with reduced carbon footprint compared to traditional HVAC systems. Its photosynthesis activity allows active CO₂ capture, which can support potential net-negative emissions. The results justify incorporating Azolla-based filtration in green building design as a sustainable and energy-efficient indoor air cleaning mechanism.</p> Graphical abstract <p></p>