4-05: Determining the degradation rate and resulting quality of aerobically-stored high moisture corn stover

Wet harvest conditions and environmental factors, which support biological activity and subsequent dry matter loss, make dry storage (less than 20% moisture) of biomass for bioenergy use impractical in many locales. Flexible storage systems, capable of handling variable feedstock moisture contents, are necessary to deliver high-quality, low-cost feedstock to the emerging bio-products market. We investigated degradation rates of aerobically-stored high moisture corn stover (50%, wet basis) using laboratory scale storage simulators. Biomass was sampled throughout the self-heating temperature profile to understand the impact of thermally active storage on feedstock quality. CO₂ generation was used to quantify microbial respiration and resulting dry matter losses over 105 days in storage. Elevated dry matter loss rates (0.4% d^-1) occurred for 60 days while temperatures remained elevated (>55°C), resulting in 35% dry matter loss after temperatures returned to near ambient. Glucan and xylan losses occurred at a rate of 0.4% d^-1 and 0.5% d^-1 at elevated storage temperatures while total losses reached 28.5% and 43.5%, respectively. While the theoretical ethanol yield of the degraded material was within 4% of the initial feedstock, storage losses represented an estimated 35% reduction in achievable ethanol yield per ton of biomass harvested. In general, the greatest losses accrued while storage temperatures remained high due to self-heating, indicating a need for storage practices capable of reducing this period in order to mitigate losses of at-risk feedstocks.