## 3 Results and Discussions
### Volatile Fatty Acids & Volatile Organic Compounds  
Table 7 summarizes the weekly average emissions of total volatile fatty acids (TVFA) and key volatile organic compounds (VOCs), including phenol, \(p\)-cresol, and indole. Contrary to the initial hypothesis that rice husk biochar would mitigate TVFA and VOC emissions, the results revealed complex and sometimes unexpected trends. TVFA emissions fluctuated over the three-week experimental period but did not show significant differences between the control and biochar treatments. This suggests that, under the given conditions, biochar had minimal influence on TVFA emissions. In contrast, phenol emissions increased with biochar addition, particularly in the 10% treatment, which showed a statistically significant rise (\(p<0.05\)). This unexpected increase may be due to the presence of phenolic compounds or their precursors in the biochar itself or changes in microbial activity favoring phenol production. Further investigation is required to determine the mechanisms underlying this response. The effect of biochar on \(p\)-cresol emissions  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Compound**} & \multirow{2}{*}{**Period**} & \multirow{2}{*}{**Control**} & \multicolumn{2}{c}{**Treatment**} & \multicolumn{2}{c}{**\(p\)-Value**} \\ \cline{4-9}  & & & **5\% Biochar** & **10\% Biochar** & & **5\% Biochar** & **10\% Biochar** \\ \hline \multirow{3}{*}{
\begin{tabular}{c} DMDS \\ (\(\mu\)g m\({}^{-2}\) day\({}^{-1}\)) \\ \end{tabular} } & 1 st week & 117.7 & 115.9 & 63.8 & 55.50 & 0.999 & 0.619 \\  & 2 nd week & ND & ND & - & - & - \\  & 3 rd week & ND & ND & ND & - & - & - \\  & Overall & 64.2 & 63.2 & 34.8 & 30.27 & 0.999 & 0.619 \\ \hline \hline \end{tabular}  
* ND = Not detected. Abbreviations: MM, methyl mercaptan; DMS, dimethyl sulfide; DMDS, dimethyl disulfide. Note: The number of measurements taken was 18 in the 1 st week, 9 in the 2 nd week, 6 in the 3 rd week, and 33 overall.  
\end{table}
Table 6: _Cont._appeared time-dependent. While no significant differences were observed in the first two weeks, the 10% biochar treatment significantly reduced \(p\)-cresol emissions in the third week (\(p<\) 0.05). This suggests a delayed effect, possibly due to biochar-induced changes in microbial communities or bedding properties over time. Indole emissions were only detected in the first week and were undetectable thereafter, likely due to rapid degradation or volatilization. No significant differences were observed between the control and biochar treatments, indicating that biochar did not have a measurable effect on indole emissions.  
These findings highlight the complex role of rice husk biochar in TVFA and VOC emissions. While biochar did not significantly impact TVFA and indole emissions, it unexpectedly increased phenol emissions and showed a delayed reduction in \(p\)-cresol emissions. These results emphasize the need for further research to clarify the mechanisms driving these changes and assess biochar's long-term impact on VOC emissions under different environmental conditions.  
Previous studies have reported varying effects of biochar on VOC mitigation, likely due to differences in biochar properties, application methods, and manure characteristics. [PERSON] et al. [12] found that applying cattle manure biochar at 10% (\(w/w\)) reduced total VOC emissions by more than 50% in a lab-scale sorption experiment. Similarly, [PERSON] et al. [39] observed a 13% reduction in NH\({}_{3}\) emissions when fine biochar (4.57 kg m\({}^{-2}\)) was applied to stored swine manure. However, their study reported no significant reduction in VFA and VOC emissions (e.g., n-butyric acid, valeric acid, isovaleric acid, \(p\)-cresol, indole, and skatole), nor sulfur compound emissions (H\({}_{2}\)S, DMDS, and Dimethyl trisulfide). These inconsistencies across studies may stem from variations in biochar and manure characteristics, biochar application method, dominant microbial consortia, and environmental conditions [49, 50].