This study presents a technical and environmental assessment of H 2 S removal using four rice husk (RH) –derived biochars produced by slow pyrolysis. Biochars were obtained under nitrogen (N 2) or carbon dioxide (CO 2) atmospheres, with and without potassium hydroxide (KOH) activation. The investigated materials included unmodified biochars (RHN 2 and RHCO 2) and biochars activated before (KOHRHCO 2) or after (RHCO 2 KOH) CO 2 -assisted-pyrolysis. Commercial activated carbon (CAC) was used as a reference. Dynamic adsorption experiments were conducted at H 2 S concentrations between 35 and 700 ppm and gas hourly space velocities (GHSV) from 3822 to 30, 573 h⁻¹. Compared to N 2, CO 2 -assisted-pyrolysis enhanced carbon content (74. 0 vs. 72. 0%), reduced H/C and O/C ratios, and improved specific surface area (SSA) (141. 0 vs. 55. 7 m²/g), and micropore volume (0. 08 vs. 0. 02 cm³/g). KOH-activation further enhanced SSA (178. 4 m²/g) and micropore volume (0. 60 cm³/g) in pre-activation, while decreasing carbon content due to potassium effects. Among the tested materials, KOHRHCO 2 and CAC showed the highest H 2 S adsorption capacities. Although KOHRHCO 2 exhibited a lower adsorption capacity than CAC at 700 ppm and GHSV of 3822 h⁻¹, it demonstrated superior environmental performance. Life Cycle Assessment results showed that KOHRHCO 2 achieved a negative global warming impact, corresponding to approximately 108% of the footprint of CAC but with an opposite sign, effectively shifting the process from carbon-intensive to carbon-negative. This outcome is attributed to the use of agricultural waste as feedstock and to carbon sequestration during CO 2 -assisted pyrolysis. Overall, CO 2 -pyrolyzed and KOH-activated RH biochars emerge as environmentally advantageous adsorbents for H 2 S removal in gas streams.
Galletti et al. (Sat,) studied this question.