3-12: Bioethanol Production from Steam Exploded Forage Sweet Sorghum at High Solid Content

The aim of this work was to determine the best operation conditions for steam explosion pretreatment of forage sorghum biomass and to test ethanol production by Simultaneous Saccharification and Fermentation (SSF) process at high pretreated solids loading.

Steam explosion pretreatment of forage sorghum was performed in a 2 L batch steam-explosion pilot unit at various experimental conditions. The effect of pretreatment temperature (180-230ºC) and time (2-10 min) on overall glucose yield was studied using a response surface method according to a rotable central composite experimental design 2². Glucose overall yield was calculated taking into account sugar recovery in the liquid fraction and sugar release from pretreated substrate by enzymatic hydrolysis laboratory tests using commercial cellulases. Optima pretreatment condition of 220ºC and 7 min resulted in a overall glucose yield of 93% of the glucose content in raw material.

The pretreated water insoluble solid fraction (WIS) from pretreatment run at optima temperature and time conditions was tested for bioconversion to ethanol by SSF in laboratory fermentors. A presaccharification step of 8 hours prior to SSF was tested in experiments at initial WIS concentrations of 10, 15 and 20% (w/v) using commercial cellulase and β-glucosidase (15-20 FPU and 15-20 IU/g cellulose in WIS, respectively). Fermenting yeast Saccharomyces cerevisiae at low inoculum (0.4-0.5 g/L) loading was used in SSF. Main results of this research will be reported.