MOISTURE EFFECT ON COMPACTION AND PERMEABILITY IN COMPOSTS

The effects of initial moisture content and compressive loads on the c ompactability and air permeability of two compost mixes, biosolids (pr imary) + bark + sawdust + recycled compost, and cow manure are describ ed. Biosolids compost in the moisture range of 42-57% was subjected to compressive stresses of 0-43.2 kPa and the degree of compaction and p ressure drops in the flow range of 0.05-0.20 m/s were measured. The re lationship between air permeability and total air-filled porosity at d ifferent moisture levels was described using the Kozeny-Carman how mod el. Biosolids showed significant compressive behavior and lower permea bilities with increasing moisture content (42-57%). Cow manure had a h igh moisture-retaining capacity and the differences in compaction beha vior and air permeabilities were small when moisture levels were varie d (57-73%). The model described the relationship between air permeabil ity and effective free air space with a high level of accuracy (R(2) > 0.95) at all moisture levels and compacted state. It was shown that i n beds of moisture levels greater than 60% (wet basis), free air space less than 30% can be reached, and fan power requirements can increase greatly with increasing depth.