Effects of Alkaline Combined with Ultrasonic Pretreatment and Enzymatic Hydrolysis of Agricultural Wastes for High Reducing Sugar Production

The effects of six pretreatments of five agricultural wastes (corn cob, pineapple waste, bagasse, rice straw and water hyacinth) on the chemical composition and total reducing sugar yield were investigated. Six pretreatments were: 1% NaOH with ultrasound for 60 min; 1% NaOH with ultrasound 100% duty; 2% NaOH with ultrasound for 60 min; 2% NaOH with ultrasound 100% duty cycle; 1% NaOH by standing in the oven at 60 degrees C for 90 min; and 2% NaOH by standing in the oven at 60 degrees C for 90 min. Among them, the highest cellulose content of 55.15% was obtained from bagasse by pretreating with 1% NaOH with ultrasound 100% duty cycle. It subsequently yielded the highest total reducing sugar of 36.21% (36.21 g reducing sugar/100 g substrate). The lignin content of all samples significantly decreased, but ultrasonic pretreatment increased the cellulose content. However, the best pretreatment method for each sample was different. Based on SEM analysis, the morphologies of all samples were changed after pretreatment. In addition, the increase of enzyme loading from 250 to 550 CMC U/g biomass led to more than 20% increase in the total reducing sugar. It was found that the higher enzyme loading (700 CMC U/g dried biomass) did not improve the total reducing sugar for all samples.