Tuesday, May 3, 2011: 3:30 PM
Grand Ballroom B, 2nd fl (Sheraton Seattle)
A method was developed to eliminate process steps for solid-liquid separation and sugar cleanup. It involves the co-fermentation of hexose and pentose sugars from dilute phosphoric acid (0.01 g phosphoric acid/g dry raw bagasse) pretreated sugarcane bagasse in a single vessel (SScF) using an initial liquefaction step (L) with cellulase (prior to inoculation) to improve mixing and saccharification (L+SScF). This L+SScF process is similar to the corn dry milling ethanol process that is well established and commercially proven. Ethanologenic Escherichia coli strain LY180 was adapted to phosphoric acid hydrolysates and a hydrolysate-resistant mutant resulted, designated MM160. Strain MM160 demonstrated improved resistance to known dilute acid hydrolysate inhibitors (furfural, 5-hydroxymethylfurfural and acetate) formed during pretreatment over the parent strain. L+SScF fermentations were performed using MM160 of dilute acid steam pretreated bagasse (160-190°C, 1% phosphoric acid, 10 min) slurries containing 10% and 14% dry weight (includes fiber plus solubles). Increasing temperature increased the amount of inhibitors and monomeric sugars present in the slurries. Pretreatment at 190°C produced slurries that were not fermentable by MM160. With lower temperatures, glucose was completely consumed by 24, 48 and 96 h for 160°C, 170°C and 180°C pretreatment slurries respectively. Xylose utilization lagged with increasing temperature and was incomplete in all cases even after 240 h. Despite the incomplete utilization of xylose high ethanol yields were obtained. The highest titer (30 g/L ethanol) and yield (0.21 g ethanol/g bagasse dry weight) were obtained after incubation for 122 h using 14% dry weight slurries of pretreated bagasse (180°C).