## 3 Results and Discussions
### Role of Pore Structure and Surface Chemistry in the Adsorption Performance of Rice Husk Biochar  
The proper configuration of micropores and mesopores plays a critical role in adsorption processes. Micropores primarily function as the main sites for adsorption due to their strong interaction with adsorbates [53; 54; 55]. Although mesopores may exhibit relatively lower interaction capacity compared to micropores, they serve also as pathways, facilitating the transport of adsorbates to the micropores for effective adsorption [56; 57; 58]. The adsorption-desorption isotherm of rice husk biochar (Figure 4) exhibits characteristics of both Type I (b) and Type IV isotherms, as described by the International Union of Pure and Applied Chemistry (IUPAC) [59]. The steep initial rise at low relative pressure (P/P\({}_{0}\) < 0.01) indicates micropore filling, a hallmark of Type I (b) isotherms, which are associated with micropores, including wider micropores and narrow mesopores (<-2.5 nm). This is supported by the t-plot analysis, which reveals that micropores contribute 26.0 m\({}^{2}\) g\({}^{-1}\) to the total specific surface area of rice husk biochar, accounting for approximately 82% of the specific surface area measured at 31.9 m\({}^{2}\) g\({}^{-1}\) (Table 2). The adsorption behavior at higher relative pressures (P/P\({}_{0}\) > 0.1) aligns with Type IV isotherms, indicating the presence of mesopores in the rice husk biochar. According to the IUPAC classification, Type IV isotherms are observed in mesoporous materials, where the adsorption process involves monolayer-multilayer adsorption followed by capillary condensation at higher relative pressures. The desorption branch exhibits a hysteresis loop resembling Type H4, which is often associated with materials containing micropores and narrow mesopores. These interpretations are consistent with previously reported classification and pore behavior in mesoporous and microporous adsorbents [59; 60; 61; 62]. The loop does not close completely, which may be attributed to diffusion limitations in micropores that hinder the release of adsorbed nitrogen molecules--possibly due to irreversible uptake--as well as to potential pore deformation during adsorption [55; 63; 64]. Figure 5 illustrates the pore size distribution of rice husk biochar. The prominent peak within the 1-2 nm range confirms a significant presence of micropores. Additionally, a smaller peak around 10 nm suggests the presence of mesopores. These results suggest that both micropores and mesopores of the rice husk biochar play significant roles in adsorbing odorous compounds. With a molecular size of approximately 0.3 nm, NH\({}_{3}\) is well-suited for adsorption within the micropores. Meanwhile, the mesopores serve as transport pathways, reducing diffusional limitations and facilitating  
Figure 4: Nitrogen adsorption-desorption isotherm of rice husk biochar. Figure 5: Pore size distribution of rice husk biochar. the movement of ammoniacal nitrogen molecules into the micropores, thereby ensuring effective utilization of adsorption sites. In addition, the reduction in DMS emissions observed in the bedded pack treated with rice husk biochar may also be attributed to its pore structure. The micropores likely acted as adsorption sites for DMS or its precursors, while the mesopores improved air permeability within the bedded pack [65]. This enhanced oxygen diffusion could have mitigated anaerobic conditions, thereby suppressing the activity of microorganisms responsible for DMS production. The FTIR spectrum of rice husk biochar exhibited peaks at 1588.1 \(\pm\) 0.2 cm\({}^{-1}\), 1047.8 \(\pm\) 19.0 cm\({}^{-1}\), 791.2 \(\pm\) 3.9 cm\({}^{-1}\), and 459.9 \(\pm\) 2.4 cm\({}^{-1}\) (Figure 6). The peak at 1588.1 cm\({}^{-1}\) corresponds to C=O stretching vibrations, with potential contributions from C=C or aromatic ring vibrations [66; 67; 68]. The peak at 1047.8 cm\({}^{-1}\) is associated with Si-O-Si stretching vibrations [66; 68; 69].