A high-performance passive strategy for indoor gaseous pollutant control using alkaline mineral-rich biochar derived from livestock manure

Effective management of indoor air quality (IAQ) is a significant public health priority due to the accumulation of hazardous gaseous pollutants, including volatile organic compounds and inorganic odorous gases. This study presents a sustainable, non-powered passive adsorption strategy utilizing the livestock manure-derived biochar (LMB) for the removal of formaldehyde (HCHO), hydrogen sulfide (H₂S), and ammonia (NH₃). The LMB, synthesized via prolonged high-temperature pyrolysis (700 °C, 4 h) to ensure a stable aromatic structure, exhibited a well-developed mesoporous matrix and abundant feedstock-derived alkaline minerals (Ca, K, and Mg). In trials corrected for natural chamber decay, the LMB demonstrated substantial removal efficiencies: 97.6% of 1 ppm HCHO was eliminated within 2 h, while H₂S (≤ 3 ppm) and NH₃ (5 ppm) achieved 100% removal within 30 and 60 min, respectively. The observed H₂S removal was facilitated by alkaline mineral-driven chemisorption and stoichiometric neutralization. Mechanistic analysis elucidated that the measured performance is attributed to the synergistic effects of physical pore-filling, hydrogen/coordination bonding with surface functional groups, and irreversible chemical fixation by inorganic components. Furthermore, scenario-based modeling evaluated the scalability of the LMB, predicting that practical dosages can mitigate pollutants in residential-scale volumes. Collectively, this study indicates that the LMB is a promising, cost-effective, and broad-spectrum adsorbent that supports IAQ improvement while promoting the circular economy through the upcycling of agricultural waste into functional materials.