Process Control based on Dynamic Properties in Composting: Moisture and Compaction considerations

Abstract

Effect of moisture levels and compactability (i.e. change in volume with load) were studied to determine their influence on aeration. Replicated experiments were conducted to measure pressure drop versus airflow using biosolids and cow manure composts at four moisture levels and loadings in the range of 0–43.2 kPa. Biosolids compost showed significant increase in compactability and pressure drops with increasing moisture levels. Cow manure compost behavior did not significantly change with increasing moisture. A generalized airflow model was developed based on the Kozeny Carman equation of permeability in porous media. The model successfully described the air permeability of the materials at all moisture and compaction levels. Data of moisture and temperature profiles during 21 days of compo sting are presented from a full scale invessel (6.1 × 3.0 × 220 m3) biosolids composting system. Based on this data and the air flow model it is quantitatively shown that management strategies using variable depth of compost can improve product uniformity and reduce operating costs. Maximum critical bed depth at different moisture levels and the potential for the formation of anaerobic conditions at different depths of the compost bed and at different moisture levels are described.