Production of Fermentable Sugars by Combined Chemo-enzymatic Hydrolysis of Cellulosic Material for Bioethanol Production

To change the recalcitrant nature of the lignocellulosic material for maximum hydrolysis yield, a comprehensive study was done by using sulphuric acid as an exclusive catalyst for the pretreatment process. The enzymatic digestibility of the biomass [Water Hyacinth: Eichhornia crassipes] after pretreatment was determined by measuring the hydrolysis yield of the pretreated material obtained from twenty four different pretreatment conditions. These included different concentrations of sulphuric acid (0.0, 1.0, 2.0 and 3.0%), at two different temperatures (108 and 121 °C) for different residence times (1.0, 2.0 and 3.0h).The highest reducing sugar yield (36.65 g/L) from enzymatic hydrolysis was obtained when plant material was pretreated at 121 °C for 1.0 h residence time using 3.0% (v/v) sulphuric acid and at 1:10 (w/v) solid to liquid ratio. The total reducing sugars obtained from the two-stage process (pretreatment + enzymatic hydrolysis) was 69.6g/L. The resulting sugars were fermented into ethanol by using Saccharomyces cerevisiae. The ethanol yield from the enzymatic hydrolyzate was 95.2% of the theoretical yield (0.51g/g glucose), as determined by GS-MS, and nearly 100% since no reducing sugars were detected in the fermenting media by TLC and DNS analysis.