Minimizing Wash Water Usage After Acid Hydrolysis Pretreatment of Biomass
Abstract Dilute acid pretreatment, needed to prepare biomass for saccharification, results in the production of a number of byproducts, which inhibit subsequent enzymatic hydrolysis and fermentation steps. In order to improve saccharification yields in the enzyme hydrolysis step, the pretreated biomass is often rinsed with room temperature water to remove these byproducts. High-density poplar was pretreated with 1% dilute sulfuric acid at 140 ºC for 40 minutes. After pretreatment the biomass was washed with water volumes equal to 0, 1 ½, or 3 times the biomass volume. The rinsed biomass was then enzymatically hydrolyzed and the concentrations of byproducts and resulting carbohydrates were quantified by high-pressure liquid chromatography (HPLC). Quantification was performed in pretreatment hydrolyzates, rinsing waters and enzyme hydrolyzates. Results show that inhibitory byproducts are highly soluble even in low amounts of wash water, and glucose yields are similar despite halving the amount of water used (3 and 1 ½ water volumes) in the wash step, signifying that the removal of a sufficient number of inhibitory compounds can be accomplished with even at small wash values. Specifically, enzymatic hydrolysis yielded between 3 and 4 grams glucose per gram dry biomass in the 1 ½ and 3 water volumes rinses, respectively, with totals at both conditions equaling between 7 and 8 grams glucose per gram dry biomass, respectively. The rinse step removed similar concentrations of inhibitors in either the 1 ½ and 3 water volume rinsing procedures.