4-09: Investigating the Impact of Storage Parameters upon Switchgrass Feedstock Quality

Large-scale, year-round manufacture of cellulosic biofuels requires medium to long-term storage due to the seasonal nature of biomass crop harvests. While the effects of storage on biomass harvested for animal forage have been researched, it is necessary to define storage impact, especially dry matter loss, on biofuel production. Moreover forage study data are largely time-invariant, focusing on end-point analysis. The objective of this study was to analyze the impact of storage parameters (moisture, temperature, and time) on switchgrass through a material balance around the constituents (cellulose, hemicellulose, and lignin) and changes in cellulose enzymatic digestibility.

Switchgrass wetted to four different moisture levels (10-12%, 15%, 18-20% and 30% by weight) was packed in perforated plastic mini-bales containing 100 dry grams each. The bales were stored at three different temperatures (<10, 20 and 35 °C) and at humidity levels designed to be in equilibrium with the bale moisture contents and minimize moisture loss over time. Bales were removed after 1, 2, 4, 8 and 12 weeks and analyzed for dry matter loss and subsequently composition changes. Storage carried out at low temperatures or with moisture contents ≤20% resulted in negligible dry matter loss. Switchgrass wetted to 30% by weight, stored at 20 °C showed <2% loss after 8 weeks. Similarly wetted bales stored at 35 °C showed 3-4% dry matter loss at 4 weeks, and 6-8% loss at 8 weeks. We report changes in biomass composition and the effect of degradation on enzymatic digestibility as a function of dry matter loss.