Effects of moisture content and soil additions on physical properties and transport phenomena for compost windrow design

Composting has been used for over a decade for bioremediation of explosives, pesticides, and various petrochemical and organic compounds. When these contaminants are present in soil, the soil itself can be added directly to the compost piles. Because the addition of soil changes the physical properties of the compost matrix in a way that affects the proper functioning of biological activity within the pile, appropriate mixture ratios are critical. This study uses a fundamental engineering approach to characterize and predict the physical properties and transport phenomena of several soil:compost blends at various moisture and compaction levels for successful windrow design. The physical properties examined in this study were permeability, air-filled porosity, and mechanical strength. A baseline compost matrix composed primarily of food waste, manure, leaves and wood chips was used as a control. Soil was added to this compost in ratios of 20:80 and 50:50, based on dry weights. The physical properties mentioned above were measured for these soil:compost mixes at approximately 25%, 45% and 65% moisture contents (wet basis). Permeability and air-filled porosity were measured at various levels of compaction, ranging from 0 to 21.7 kN m^-2. Results show that moisture content has a larger effect on permeability, air-filled porosity, and mechanical strength than soil content. When moisture content increases, permeability, air-filled porosity, and mechanical strength decrease. Soil additions affect these properties to a lesser extent. In general, it was found that the amount of soil that can be added to a compost mixture decreases with increasing moisture content.