(643c) Physical and Microbial Modeling of Aerobic Switchgrass Degradation

A model has been developed to integrate heat and mass transfer aspects with microbial growth to describe the degradation of switchgrass using forced aeration. Microbial growth kinetics incorporated the use of three major microbial populations; namely, bacteria, fungi and actinomycetes, each of which was specific to different substrate components (sugars and starches, hemicelluloses, cellulose and lignin). The energy transfer components account for the removal of energy via the bulk flow of air, energy accumulation in the substrate bed and the generation of heat from microbial activity. Model predictions captured well the dynamics obtained experimentally between physical and microbial variables. A sensitivity analysis was performed to determine the effects of the key model parameters of initial moisture content, the oxygen uptake rate, substrate yield coefficients and population growth constants. This analysis showed that higher initial moisture content produced a higher maximum temperature and that substrate-specific and microbial population-specific constants also greatly impacted the dynamic behavior predicted by the model. Overall, the model agreed well with experimental data and has the potential to become a predictive tool for substrate degradation during solid state fermentation processes