(564a) Two-Phase Bioconversion Process for Effective Utilization of Hexoses and Pentoses in Corn Stover

An integrated bioconversion process was developed to achieve high ethanol yield and concentration using xylan-rich soaking in aqueous ammonia (SAA)-pretreated corn stover. The SAA has been proven to be effective for pretreatment of corn stover, which results in high retention of xylan with the solid. We devised a novel two-phase bioconversion process utilizing SAA-pretreated solid. This approach is designed to convert C5 sugars (>85% of xylan) with minimal glucose conversion (<15%) in the first stage and C6 sugars in the second stage, and thus effective utilization of both sugars can be achieved. This proposed bioconversion scheme of C5 sugars in the 1st phase followed by C6 sugar conversion in the 2nd phase is feasible because: the cell wall polysaccharides consist of crystalline cellulose fibrils surrounded by a matrix of non-crystalline hemicelluloses. A reversed bioconversion scheme (C6 sugar conversion before C5) is not feasible because hydrolysis of hemicellulose structure precedes cellulose hydrolysis.

The effects of various enzymes on SAA-treated substrate were investigated. This paper provides experimental details and overall assessment on corn stover-to-bioethanol by two-phase bioconversion process. The results support that two-phase fermentation of SAA-treated corn stover to ethanol is quite feasible.