Cost and performance estimates of corn stover in a wet logistics system

A large portion of feedstock is harvested with moisture contents that exceed 20%, a threshold for microbial and fungal growth that results in compositional changes and loss in storage. Storing corn stover in wet, anaerobic storage is an active management approach to reduce the risk of significant aerobic degradation and catastrophic loss due to fire. A wet, bulk logistics system is based on particle size reduction early in the supply chain through field-chopping, which removes the dependency on field-drying prior to baling and allows for an expanded harvest window. In this study, forage chopping was capable of size reducing 60-85% of corn stover below 1 inch diameter, reducing the need for further preprocessing. Two storage methods compatible with wet corn stover are ensiling, which is based on manual compaction to limit air infiltration and promote fermentation, and a modified-Ritter pile, which is formed and simultaneously compacted using slurried biomass. Laboratory reactors (100 liter) were used to determine storage performance; dry matter losses over 110 days were 5.9% (±1.1%) in ensiling and 10.1% (±0.6%) in modified-Ritter storage. No significant change in structural sugars occurred during storage, although total extractives and soluble sugars decreased significantly. An economic analysis of a fully-wet logistics system with on-site storage at a biorefinery showed that Ritter storage would incur 25% higher costs than ensiling at the central storage facility. Both wet storage approaches are cost competitive with a feedstock logistics system that relies on dry bales, meanwhile providing an active control for loss in storage.