Poplar (Populus deltoides L.): The Effect of Washing Pretreated Biomass on Enzymatic Hydrolysis and Fermentation to Ethanol

In this work, Populus deltoides L. biomass was pretreated in 0.98% (v/v) sulfuric acid at 140 °C for 40 min. Prior to enzymatic hydrolysis, pretreated biomass was either not washed or washed with 1.5 or 3 volumes of water, as compared to biomass. Rinsing the pretreated biomass with 1.5 or 3 volumes of water resulted in glucose yields that were seven times greater than the nonwashed treatment. Pretreatment hydrolyzates, wash waters, and enzymatic hydrolysis hydrolyzates were analyzed for carbohydrate, aliphatic acid, aldehyde, and phenolic content. An analysis of the wash waters showed the presence of gallic, vanillic, syringic, p -coumaric, ferrulic, trans -cinnamic, and salicylic acids at concentrations below 0.07 mg mL –1 . Washed and nonwashed enzymatic hydrolyzates showed significant differences in gallic, vanillic, ferrulic, and salicylic acid concentrations, indicating that these compounds could be in part responsible for inhibiting enzymatic hydrolysis. Nonwashed and washed enzymatic hydrolysates were fermented to ethanol with self-flocculating SPSC01 and nonflocculating ATCC4126 yeasts. While the biomass washed with 3 volumes of water produced the highest ethanol yields (up to 0.43 g g –1 glucose) and were significantly higher than those from the nonwashed sample (≤0.28 g g –1 glucose), the ensuing differences between samples washed with 3 and 1.5 volumes of water were not significant. The SPSC01 strain generally outperformed the ATCC4126 strain in ethanol fermentation efficiency, in particular when the nonwashed hydrolysates were used as feedstock.