(718c) Ozone Pretreatment of Compacted Switchgrass

Ozone pretreatment has been shown to improve the enzymatic digestibility of cellulose. In this study, the chemical pretreatment of highly compacted switchgrass with ozone was carried out in a fixed bed reactor. Material density in the reactor, ozone concentration, and biomass particle size simulated large scale in-farm or conversion facility treatment of biomass bales. An industrially viable ozone concentration of 22.5 mg/l (15% w/w) was used to treat the samples for 24 hrs. The results showed that a significant amount of soluble sugars (about 10% of total sugars) was generated from ozone-catalyzed hydrolysis of the hemicellulose. Despite visible changes in color, compositional analysis showed no significant change in glucan content and insignificant changes in total lignin content after treatment. Nonetheless digestibility of treated material increased by more than 5 fold. Enzymatic hydrolysis of the materials with a relatively low loading of 10 FPU/g glucan resulted in yields of glucose of 59% for water washed samples and 27% for unwashed, compared to 11 and 9 % for non-treated samples, respectively.  The significant improvement in hydrolysis yields for washed samples suggest that water-soluble inhibitors generated from lignin degradation may be present after ozone pretreatment.