(625an) Evaluation of Bulk, High Moisture Corn Stover Performance in Anaerobic Storage

Fires in bale storage yards and variable feedstock quality in outdoor-stored bales have prompted industrial and DOE program interest in alternative storage methods. Wet anaerobic storage of corn stover is being explored as a means to provide year-round feedstock supply to biorefineries while reducing the risk of loss due to fires or aerobic microbial degradation. Wet-harvested feedstocks also have the potential to reduce pretreatment severity requirements for conversion to biofuel compared to senesced feedstock. Laboratory reactors (100 liter) were used to simulate field conditions and determine the storage performance of corn stover in traditional ensiling at 50% moisture (wet basis) and modified-Ritter storage at saturation, approximately 75% moisture. In the modified-Ritter storage method, a storage pile is formed using slurried biomass and compacted by the weight of water. The water in the Ritter method is recirculated during pile construction and is capable of removing soluble components such as soil-based ash and macronutrients. This method was simulated in the laboratory by washing biomass with 3 volumes of water per kg corn stover, which successfully removed ash, N, P, and K. Anaerobic conditions were reached in the Ritter method within 7 days, while 1% oxygen was still present in the traditional ensiling approach after 80 days in storage. However, a three-fold increase in gas production was observed in the Ritter storage compared to traditional ensiling, with up to 65% CO₂ in the Ritter storage compared to 25% CO₂ in traditional ensiling. Trace levels of CH₄, H₂, and NO_x were observed in both storage conditions, while N₂O and NO₂ were detected only in the Ritter storage method. These results suggest that the corn stover in the simulated Ritter storage underwent a greater degree of microbial degradation than in the silage pile. Storage performance was also measured in terms of total dry matter loss, compositional analysis, and conversion to ethanol in a commercial process. Overall, wet anaerobic is a promising method for limiting dry matter losses and reducing the risk of catastrophic loss of feedstock to fire.