Determination of Initial Bulk Density in Different Depth Layers of Composting

Different depth layers of composting materials have different bulk densities due to compaction of the upper pile onto the lower pile. Determining the bulk density of compost at different depths without disturbing the composting process is difficult. In this study, the densities of mixtures of animal manure (pig manure or chicken manure) and amendment material (corn stalks or peanut shells) at various water contents were measured using a custom measuring device. The materials were placed in barrels, and then different loads were applied to the materials by placing known masses on top of the material. Different pressure values indicate different depths, so the bulk density of different layers in a compost pile can be determined. Bulk density (ρ) and pile height (h) follow ρ = AhB, where A is a fitting parameter that depends on the initial bulk density of the material, and exponent B is a dimensionless indicator of the physical compressibility of the material. The most compressible materials were the mixtures of pig manure and corn stalks (61% water content) and chicken manure and corn stalks (61% water content), followed by the mixtures of chicken manure and corn stalks (65% water content) and chicken manure and peanut shells. The initial bulk density and free air space (FAS) of different compost materials at different depths can be determined using the measuring device. These data will be useful in developing reasonable designs for composting facilities.