Abstract
A numerical model simulating airflow pattern, heat and mass transfer, and degradation in the twodimensional cross-section of a deep bed composting vessel was developed. The model accounts for compressibility of thematerial and predicts spatial and temporal changes in state variables. The model was validated at a commercial facilitythat composts a mix of biosolids, bark and sawdust. Simulations were performed to quantify the effects of (1) initialmoisture level, (2) depth of bed, (3) ambient air temperature, (4) cooling air recirculation, (5) material degradability and(6) blockage of plenum, on cost of aeration and spatial homogeneity of degradation within the vessel. Results show thatcost of aeration is lowest when the material is at an initial moisture level of 55% and the bed depth is 3.5 m. Energyrequired per unit of dry matter degraded decreases as the ambient temperature increases. The increased aerationrequirement when cooling air was recirculated was quantified, and shows that overall energy requirements are reduced byrecirculating air. Aeration energy requirements and system throughput were compared under different operatingparameters.
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