# Exploring Effective Bio-Cover Materials for Mitigating Methane Emission at a Tropical Landfill
## 4 Conclusions  
Compost was found to be the most effective bio-cover material for mitigating methane emission from the tropical landfill examined in this study. Comparable field performance was also observed for sandy loam material. Stabilized waste could also be applied to mitigate methane at lower loading rates. Methane removals of 78.0-94.8% took place at the bottom part (0.20 m from inlet) of the material layer whereas the total removals of 97 to >99% were achieved in the whole material layer of 0.60 m depth. Higher methanotrophic activities and methanotrophic microorganisms were observed for compost and sandy loam materials compared to stabilized wastes. The majority of methane was possibly removed through biological oxidation in the bio-cover materials as fugitive emissions at the surface of the bio-cover material layer were low (<2% of methane loading).  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13031990/s1](https://www.mdpi.com/article/10.3390/app13031990/s1)]([https://www.mdpi.com/article/10.3390/app13031990/s1](https://www.mdpi.com/article/10.3390/app13031990/s1)), Figure S1. Variation of rainfall and ambient temperature; Figure S2. Variation of methane loadings (MLRs) and removals (MRRs) during bio-cover operation; Figure S3. Variation of methane emissions (MERs) during bio-cover operation; Figure S4. PCR-DGGE profiles of methanotrophic population observed in different materials (left) C (middle) SW (right) SL media; Table S1. Probes used in microbial population identification; Table S2. Moisture content (%) in bio-cover material; Table S3. Bio-cover material characteristics.  
Conceptualization, C.C. and W.C.; methodology, C.C. and W.C.; validation, R.C., W.C. and C.C.; investigation, R.C.; data curation, R.C.; writing--original draft preparation, R.C.; writing--review and editing; C.C.; funding acquisition, C.C. All authors have read and agreed to the published version of the manuscript.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Period**} & \multirow{2}{*}{**Media**} & \multicolumn{4}{c}{**Number of Methanotrophic Cells (Cell \(\times\) 10\({}^{6}\)/g Dry Solids)**} \\  & & & **Type I** & & & **Type II** & \\ \hline  & & **SL** & **C** & **SW** & **SL** & **C** & **SW** \\ \hline \multirow{3}{*}{Wet} & 0–0.20 & 10.2 & 30.3 & 8.4 & 27.2 & 35.5 & 9.3 \\  & 0.20–0.40 & 10.1 & 9.33 & 10.4 & 28.5 & 32.8 & 9.6 \\  & 0.40–0.60 & 11.1 & 11.1 & 10.7 & 30.1 & 26.7 & 10.9 \\ \hline \multirow{3}{*}{Dry} & 0–0.20 & 36.1 & 24.2 & 13.3 & 16.9 & 19.9 & 9.7 \\  & 0.20–0.40 & 35.5 & 28.7 & 13.8 & 17.2 & 24.9 & 14.7 \\ \cline{1-1}  & 0.40–0.60 & 34.6 & 24.9 & 19.6 & 25.1 & 23.6 & 16.9 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Methanotroph population in the bio-cover materials.  
**Funding:** This research was financially supported by the National Research Council of Thailand through the Kasetsart University Research and Development Institute (Research grant No. 79.60). Partial support through collaborative research from ASEAN University Network/Southeast Asia Engineering Education Development Network (AUN/SEED-Net) is also acknowledged.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available in the Supplementary Materials. The other additional information is available upon request from the corresponding author.  
**Conflicts of Interest:** The authors declare no conflict of interest.