Biological Pretreatment of Lignocellulosic Biomass during Wet Storage and Its Impact on Downstream Biorefinery Processes

Storage and pretreatment of lignocellulosic biomass are both significant challenges facing the growing biorefinery industry. In humid environments, ensilage is a traditional biomass storage technique, which could be used to preserve the feedstock prior to bioconversion into ethanol. Under moist, anaerobic conditions, microorganisms convert the soluble sugars of the ensiled biomass into organic acids, resulting in low pH and minimizing further biomass degradation. Ensilage, either alone or with added biocatalysts, may have benefits as a combined storage and biological pretreatment strategy which is less energy and cost intensive. The goal of this work is to quantify these possible benefits. Variables considered include: feedstock (switchgrass and corn stover), silage duration (7-21 d for stover, 21 d-1 yr for switchgrass), experimental scale (lab mini-silos and field bales), and treatment during ensilage (enzymatic and microbial). Enzymatic treatments consisted of cellulase, hemicellulase, and/or ligninase addition while microbial treatments included inoculation with white-rot fungi before or after ensilage. These combined storage and pretreatment strategies were evaluated by using silage samples in enzymatic hydrolysis or simultaneous saccharification and fermentation reactions to quantify benefits in terms of sugar and/or ethanol yields.