Date of Award

Fall 2013

Degree Type


Degree Name

Doctor of Philosophy (PhD)


Agricultural and Biological Engineering

First Advisor

Nathan S. Mosier

Committee Chair

Nathan S. Mosier

Committee Member 1

Michael R. Ladisch

Committee Member 2

Dennis R. Buckmaster

Committee Member 3

Keith D. Johnson


The successful utilization of lignocellulosic biomass as a feedstock for fuels and chemicals necessitates storage for 2-6 months. It is correspondingly important to understand the impact of storage parameters - moisture concentration, temperature and duration - on biomass quality.

As aerobic storage is the most viable large-scale solution, aerobic storage experiments were carried out with three projected bioenergy feedstocks - sweet sorghum (Sorghum bicolor) bagasse, corn (Zea mays) stover and switchgrass (Panicum virgatum). Stored samples of each were examined for dry matter loss and composition change to develop a material balance around carbohydrates and lignin.

A mean dry matter loss of 24% was observed at 8 weeks in sweet sorghum stored at high moisture content (26% w/w). Soluble sugars predominated the dry matter loss in high-moisture sorghum, causing an increase in the mass fraction of lignin in the biomass. In comparison, low-moisture (12% w/w) samples showed negligible loss. High-moisture sorghum dried from 26% to 20% in 8 weeks, and further to 8% in 24 weeks.

To control moisture loss in subsequent experiments, switchgrass and corn stover were wetted to specific water activities (aw) and stored under equivalent controlled humidities.

Switchgrass stored at water activities of 0.65-0.85 showed no dry matter loss, irrespective of storage temperature or duration. Switchgrass stored at a water activity of 0.99 (~33% w/w moisture) showed significant dry matter loss at temperatures of 20 and 35 °C, although substantial sample-to-sample variation was observed at 20 °C compared to 35 °C. At 8 and 16 weeks, switchgrass stored at 0.99 aw and 35 °C lost 7% dry matter on average. Corn stover was stored under similar conditions (35 °C, 0.97 aw) for 8 weeks. The stored samples showed 10% dry matter loss on average. The dry matter losses predominantly consisted of cellulose and hemicellulose, resulting in the mass fraction of lignin increasing in switchgrass from 26.6% to 27.0% in 8 weeks and 28.8% in 16 weeks, and in stover from 23% to 25% in 8 weeks.