Evaluation of different pretreatments of Napier grass for enzymatic saccharification and ethanol production

Due to its fast-growing and high carbohydrate content, Napier grass has a great potential to be chosen as a raw material for renewable energy production. The Napier grass after different pretreatments was tested for simultaneous saccharification and fermentation (SSF) with dried yeast (Saccharomyces cerevisiae) and cellulase (CTec2) to produce ethanol. For alkaline pretreatment, the grass was incubated with 10% NaOH at a ratio of 1:20 (w/v) at 90 degrees C for 1 hour. For dilute acid pretreatment, the grass was soaked with 1% H2SO4 at a ratio of 1:10 (w/v) and incubated at 120 degrees C for 1 hour. For the two-stage pretreatment, the resultant solid from dilute acid pretreatment was further treated with 2% NaOH (1:10 w/v) at 80 degrees C for 6 hours. After enzymatic saccharification at 50 degrees C and pH 5.0 for 96 hours using CTec2, yields of glucose from three pretreated Napier grass samples (10% water-insoluble solids, WIS) were 75.4 +/- 2.9%, 55.4 +/- 6.5%, and 76.4 +/- 5.0%. Using 10% WIS of alkaline-pretreated Napier grass biomass as the substrate, the 72-hour SSF led to an ethanol yield of 86.6 +/- 3.4%. On the basis of the dried biomass of Napier grass as the raw material, the ethanol yield could reach 0.143 +/- 0.006 (g/g). Napier grass biomass could be effectively treated by alkaline, dilute acid, or two-stage pretreatment methods to remove non-cellulosic components to some extent. Alkaline pretreatment was found to be superior to dilute acid and two-stage pretreatment methods, based on ethanol yields obtained under similar SSF conditions.