Ozone treatment of biomass to enhance digestibility

Abstract

Lignin is the most abundant noncarbohydrate biological material. Pure lignin does not occur in nature; instead it is combined with plant polysaccharides as a composite called lignocellulose (Holtzapple, 1993c). Lignin combined with cellulose is very resistant to enzymatic degradation. Lignocellulosic materials require pretreatment to enhance their digestibility. The main objective of this research was to further enhance the digestibility of biomass (bagasse) with ozonation as a follow-up treatment to lime. Determining the optimum ozonation conditions such as time, pH, temperature, particle size, and water loading was essential for enhancing digestibility. The effects of sonication were also studied to determine if higher digestibility was achieved. Bagasse was ozonated for 7 min at a flowrate of 10 mL gas mixture/(g dry biomassm̕in) with a gas mixture of oxygen and ozone, where the ozone concentration varied from 9.5 to 13 wt%. To determine the effect of ozonation, material was enzymatically hydrolyzed with an enzyme loading of 5 FPU/g dry biomass for 72 hours at pH 4.8 and 50⁰C. Sugar production was measured using the DNS assay (Miller, 1959). Time, pH, and water loading were determined to be the significant factors to obtain higher digestibility. The optimum pH for ozonation was found to be 12. The recommended water loading was 20 mL/g dry biomass. Temperature, particle size, and sonication were found to have no significant effect on digestibility.