Evaluation of Storage Effect on the Biomass Conversion to Sugars Using Alkaline Pretreatment

Dry matter loss (DML) occurs in high-moisture storage conditions; it remains unclear how storage conditions and degradation impact sugar release and fermentation inhibitor production during conversion.  Two feedstocks, switchgrass (SG) and corn stover (CS) were compared using compositional analysis, alkaline pretreatment, and enzymatic saccharification. Switchgrass samples were recovered after 18 months of storage in uncovered stacks from the top, middle and bottom bales. Degraded stover samples were produced using INL’s laboratory storage reactors; samples were recovered after 3 months of storage.  The SG samples from the top and bottom bales remained wet in storage and accumulated dry matter losses up to 30% over 18 months. The inner bales remained dry and incurred losses of < 10%. Glucan and xylan losses were proportional to DML. Sugar release was decreased in samples from the top bales, which suffered the greatest DML relative to the starting materials and the other sampled locations. Switchgrass samples from the middle and bottom bales produced more sugars after pretreatment and saccharification.  After three months storage, CS with high moisture content (50% mc) was more reactive with increased glucose (from 51% to 70%) and xylose (from 24% to 35%) yields. Results show the impact of storage-related degradation on feedstock reactivity. Under the tested conditions, SG from the middle and lower bales (10% and 20% DML) and CS with high moisture content (30% DML) achieve higher sugar yields compared to the samples before storage. Results suggest that conversion conditions may require optimization to utilize degraded feedstocks efficiently.