Variations in moisture content and composition of stored Miscanthus x giganteus

Miscanthus x giganteus is a warm-season, high yield biomass crop and a great potential source for renewable energy conversion and production. Like all feedstocks the quantity and quality of miscanthus needs to be preserved during storage. Dry matter losses (DML) during storage are caused by multiple factors such as wind and rain erosion, leaching, high temperatures, and microbial oxidation. Compositional changes are affected by moisture content, temperature, substrate availability, porosity, and air diffusion rates into the biomass. In this study, bales of miscanthus were stacked (3.66 x 2.44 x 2.74 m³, L x W x H) and stored at the Energy Biosciences Institute (EBI) Farm in Urbana, IL for a period of nine months, with or without tarp cover. Weather conditions during the storage period were also recorded. After nine months, two stacks - one with tarp cover and the other without tarp cover - were sampled to assess distribution profiles of moisture content and composition. These results were used to verify a computational fluid dynamics (CFD) model being developed for simulating heat, moisture, and carbon dioxide migration through stored baled biomass. The average moisture contents at the end of the study were 11.4% for bales in a stack covered with tarp and 11.1% for those in a stack without tarp cover. Bale storage stack with tarp had a predicted DML value of 0.77% and estimated carbohydrates loss of 1.71 ± 0.81%. However, the bale storage stacks without tarp, the predicted DML accumulation value was 9.24% and observed estimated carbohydrates loss of 0.56 ± 0.5%. Additional sampling and a review of the assumptions made regarding moisture migration in the bale stacks in this ongoing study are warranted to verify the results of the physical sampling tests conducted and predictions made using the CFD model.