# Experimental Characterization of the Engineering Properties of Landfill Compost-Biocover
## 3 Results and Discussions
### Moisture and Density Relationships  
Figure 5 shows the compaction curve of the compost material. The compaction tests were carried out for a wide range of water content on both sides of optimum water content, which was conducted to observe the behavior of compost for a lower and higher degree of saturation. Figure 4: Methanotrophs in the compost material. As expected and similar to other studies, in [PERSON] and [PERSON] (2019) and [PERSON] et al. (2019), it can be seen that the dry density increases as the water content increases until it attains a maximum value of 1200 kg/m\({}^{3}\) at an optimal water content level of 79%. After that, the dry density decreases with increased water content, and this behavior continues for the wet optimum segment. The Proctor curve on the optimum dry side represents a gradual rise to the optimal water content, showing a wide range of changes in water content from 38% to 79% on the dry optimum segment rather than on the wet optimum segment from 79% to 107%. This is because for the wet optimum segment, the water added only fills the pores and water drainage is needed to obtain larger density for the higher water content. Generally, as in Figure 6, the porosity of the studied material varies from 57 to 65% for water content from 38% to 107%, and these values are in good agreement as reported by [PERSON] et al. (2019) and [PERSON] et al. (2019) for two manure compots and red turf derived from volcanic ash, respectively. [PERSON] et al. (2019) stated that the CH\({}_{4}\) oxidation process is associated with the O\({}_{2}\) penetration capability of landfill cover soil. The soil composition, particle size, and porosity are considered to have significant influences on O\({}_{2}\) transport and thus on the CH\({}_{4}\) oxidizing capacity of the biocover material ([PERSON] and [PERSON], 2019). It is well understood that a low permeable cover reduces rainfall infiltration, which results in the saturation of cover material during the rainy season. The cover may also face a desiccation problem during the dry season ([PERSON] and [PERSON], 2019). The diffusion coefficient is a function of degree of saturation and free air space which may significantly affect the performance properties of landfill biocover material for CH\({}_{4}\) oxidation potential. Figure 7 illustrates the relationship between water content and degree of saturation of the compaction curve, and Figure 8 represents the relationship between water content and FAS of compost materials. It can be seen from Figure 7 that, as expected, S increases with an increase in water content up to the optimal water content. The S increases gradually for the dry optimum segment until reaching the Proctor optimum. After this point, the S is almost the same for the wet optimum segment, showing that most voids are filled with water. Studies have shown that when the degree of saturation reaches approximately 85%, gas diffusion should be completed in the liquid phase, which is much slower than the gas phase ([PERSON], 2019; [PERSON] and [PERSON], 2019; [PERSON] and [PERSON], 2019), and similar to this, as in Figure 9, the studied material also shows minimal diffusivity potential at 85% degree of saturation. It can radically decrease CH\({}_{4}\) oxidation due to the lack of both O\({}_{2}\) and CH\({}_{4}\) in the biocover ([PERSON] and [PERSON], 2019). Figure 5: Standard compaction curve for compost material. Figure 6: Relationship between porosity vs. compaction curve of compost material. Figure 7: Relationship between the degrees of saturation vs. compaction curve of compost. Thus, from an analysis of Figures 7 and 9, it can be concluded that the compacted compost materials with an initial water content higher than 74% (corresponding to the point with a degree of saturation of 85%) show low CH\({}_{4}\) oxidation capacity and are thereby unsuitable for landfill biocovers.