Quantitative Effects of Washing Dilute Acid Pretreated Biomass in the Retrieval of Monomeric Sugars through Enzyme Hydrolysis and the Subsequent Fermentation of Recovered Sugars into Ethanol

Second generation biofuel production from cellulosic feedstocks requires a multiple step processing chain that includes pretreatment hydrolysis to fermentation and eventually distillation. The byproducts formed in the initial pretreatment of the biomass have inhibitory effects on downstream processing operations, and overcoming this inhibition is a significant challenge in cellulose to ethanol processes. Current practice is a 'washing' process in which inhibitory compounds generated in pretreatment are diluted and filtered. To determine the effect of washing on the eventual fermentation of sugars derived from biomass, poplar hybrid Populus deltoides biomass underwent dilute acid pretreatment (1%) for 40 minutes at 140 C in a stirred Parr batch reactor. The hydrolysate was then filtered and the retrieved pretreated biomass washed with 3, 1.5, or 0 volumes of wash water. The washed biomass was then enzymatically hydrolyzed (Accellerase©1500 Genencor), and the released carbohydrates fermented in a shake flask with two yeast strains. The results indicated that a significant decrease in sugar yields occurred; for 3, 1.5, and 0 wash volumes glucose concentrations were 3.74, 3.42, and .72 g/ respectively. Fermentation was found to only be slightly inhibited at equal carbohydrate levels. No significant difference was found between yeast strains in fermenting the sugars produced from different wash volumes. Hydrolysates were also tested for phenolic degradation compounds such as those listed in Ximenes (2011), but were either not detected or were present in trace amounts below inhibitory levels.