Effect of anatomical fractionation on the enzymatic hydrolysis of acid and alkaline pretreated corn stover.

Due to concerns with biomass collection systems and soil sustainability there are opportunities to investigate the optimal plant fractions to collect for conversion. An ideal feedstock would require a low severity pretreatment to release a maximum amount of sugar during enzymatic hydrolysis. Corn stover fractions were separated manually and analyzed for glucan, xylan, acid soluble lignin, acid insoluble lignin, and ash composition. The stover fractions were also pretreated with either 0%, 0.4%, or 0.8% NaOH for 2 h at room temperature, washed, autoclaved and saccharified. In addition, dilute sulfuric acid pretreated samples underwent simultaneous saccharification and fermentation (SSF) to ethanol. In general, the two pretreatments produced similar trends with cobs, husks, and leaves responding best to the pretreatments, the tops of stalks responding slightly less, and the bottom of the stalks responding the least. For example, corn husks pretreated with 0.8% NaOH released over 90% (standard error of 3.8%) of the available glucan, while only 45% (standard error of 1.1%) of the glucan was produced from identically treated stalk bottoms. Estimates of the theoretical ethanol yield using acid pretreatment followed by SSF were 65% (standard error of 15.9%) for husks and 29% (standard error of 1.8%) for stalk bottoms. This suggests that integration of biomass collection systems to remove sustainable feedstocks could be integrated with the processes within a biorefinery to minimize overall ethanol production costs.

Effect of stover fraction and storage method on glucose production during enzymatic hydrolysis.

One avenue for overcoming the economic challenges associated with the production of ethanol from renewable resources is to reduce the cost of the biomass feedstock. The balance between storage costs and benefits depend on the storage method and composition changes of individual stover fractions. Corn stover from bales stored inside and outside of a barn was separated into an interior and exterior layer after approximately 10 months of storage. The cobs, stalks, and leaves and husks were separated, dried, and ground through a 2 mm screen. Stover, sodium acetate (buffer), cellulase, and deionized water were added to 125 ml flasks. The mixture was held at 50 degrees C in an incubator and samples taken for glucose determination. The average glucose concentration after 60 h of hydrolysis from cobs, leaves and husks, and stalks was 10.5, 9.6, and 3.1 g/l, respectively. Cobs, leaves, and husks produced over 300% more glucose than stalks. Storage outside of the barn decreased the glucose production from individual stover components between 4% and 8%. The effect of stover fraction type on glucose production was significant, while the storage treatment effect was not significant. Fractionation of corn stover may be a method to increase the value of corn stover as a feedstock for glucose production.