Maximizing potential sugar yield by increasing biomass moisture content prior to pretreatment

In order to meet current and future demands for cellulosic bioethanol, biorefineries utilizing lignocellulosic biomass to produce ethanol must be run as efficiently as possible. These future biorefineries will likely utilize biomass from multiple sources. While characteristics like particle size can be specified and controlled, storage and shipping may cause non-uniformity in the chip moisture content. Maintaining uniform biomass moisture content is essential for consistency and maximizing efficiency of downstream processes.

The moisture content (MC) of fresh chipped hybrid poplar was reduced from the never dried state (50% MC) by air drying to 10% and 35% MC and oven drying to 0% MC. Moisture was then re-introduced to these samples by soaking them overnight in water to bring the moisture content back to ~55%. All samples were subjected to impregnation with 3% wt/wt SO₂ and steam explosion at 195°C for 5 minutes. Pretreated solids were enzymatically hydrolyzed at 5% consistency and 2.5 FPU/g cellulose cellulase enzyme loading for 96 hours. There was a significant increase (18-29% improvement) in hydrolysability between chips with low MC at the time of pretreatment (0% and 10%) and those that had greater than 35% MC. Soaking the dried chips in water prior to pretreatment resulted in an “evening out” of hydrolysis yields, with all of the pretreated substrates exhibiting the same hydrolysis yields regardless of their initial moisture content. These results indicate that chip MC at the time of pretreatment is highly influential on downstream processes, but can be easily controlled by rewetting dried chips.