EFFECTS OF AERATION STRATEGIES ON THE COMPOSTING PROCESS: PART II. NUMERICAL MODELING AND SIMULATION
2005
A two-dimensional finite difference numerical model of composting was developed based on a two-component
first-order kinetic model and heat and mass balance equations. Data for validation of the numerical model used results from
four different pilot-scale composting systems built to investigate these aeration strategies. Results of temperature profiles for
the simulations showed strong correlation with experimental data for layers 2, 3, and 4 (inner layers) in the system but
indicated a need to strengthen the model’s simulation of boundary condition effects (layers 1 and 5). Based on the simulations,
one-directional airflow yielded the highest temperature gradients during composting, whereas air recirculation and air
recirculation with reversed-direction airflow had the smallest temperature gradients. Model prediction of moisture content
was highly accurate for the middle layers since they were less affected by boundary condition effects. Other layers were
affected by boundary conditions and the physical phenomenon occurring in the headspace of the reactor. Reversing the
direction of airflow with and without air recirculation reduced moisture gradients. Moisture retention was increased with
reversed-direction airflow. As a result of gradients in the process variables, decomposition gradients existed. The
decomposition gradients were highly variable in the experimental studies and were not highly correlated with the simulation
results.
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