Effects of different pretreatment methods on enzymolysis characteristics of rice straw stalk in solid state

Abstract: The characteristics of enzymolysis of rice straws pretreated by natural stacking, ultrasonic wave, NaOH solution and H2SO4 solution were investigated in this work, and the physical and chemical structures of these rice straws were analyzed by SEM, FTIR and X-ray. As for natural stacking pretreatment, 50 g rice straw with 2-4 cm length in a 1000 mL beaker was mixed with 200 mL distilled water, and then the beaker was sealed against water evaporation. The substrate was fermented by natural stacking at 30℃ and a 4.0 g substrate sample was taken at intervals of 0, 3, 6, 9, 12 d respectively, and dried and ground. As for NaOH pretreatment, 50 g rice straw with 2-4 cm length immersed in 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0% NaOH solutions at ratio of 1:10 (g/mL) was pretreated for 24 h at 30°C, respectively. After that, the treated substrate samples were individually washed with water to be neutral, and ground after drying. In the process of acid pretreatment, 50 g substrate immersed in 1%, 5%, 10%, 15%, 20% and 25% H2SO4 solutions at a rate of 1:10 (g/mL) was treated for 24 h at room temperature of 30℃, respectively. Then, the treated substrate samples were individually washed with water to be neutral and ground after drying. During the ultrasonic pretreatment, the substrate grounded with 30 meshes at solid/liquid ratio of 1:15 was pretreated by ultrasonic wave at power of 180 W under ice bath condition. The ultrasonic times were set at 5, 10, 20, 30, 40 and 60 min, respectively. 4.0 g above pretreated substrate sample was autoclaved for enzymatic substrate. The results indicate that the lignin and hemicelluloses which wrapping outside the cellulose could be removed under optimal pretreatment methods and parameters, and the hydrolysis efficiency of straw stalk was improved. However, severe conditions of pretreatment would drop the enzymatic efficiency due to recrystallization of cellulose. The peak yield of reducing sugar with 126.3 mg per gram substrate was obtained from rice straw pretreated by 1.0% NaOH solution in the experiment.