Long-term kinetics of corn stover bioconversion in an enzyme enhanced mixed culture fermentation

Ensilage offers intriguing opportunities for on-farm bioconversion of crop bio mass into value-added chemicals and energy products. Previous work has demonstrated the efficacy of enzyme enhanced ensilage to convert crop residues to organic acids and fermentable sugars over a 3 to 6 week period. This study extended the time scale of this analysis to evaluate process kinetics during a six month biomass storage/pretreatment process. Corn stover at three different particle sizes was ensiled with and without a commercial enzyme mixture with a hemicellulase:cellulase ratio of 1:2.54, applied at a hemicellulase rate of 1670 lU/kg dry mass. Triplicate 20 L mini-silos were removed and analyzed on days 0, 1, 7, 21, 63, and 189. Measurements included organic acids, water soluble carbohydrates, fiber fractions, pH, and microorganisms including lactic acid bacteria and clostridia. Enzymatic addition did improve the ensilage process, as indicated by sustained lower pH, inhibition of clostridia spores, and increased lactic acid production. The middle particle size range (<10 mm) demonstrated the most promising results, although size reduction was not necessary for successful stover bioconversion.