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Study on Ultrasound-assisted Acid Pretreatment of Rice Straw and Its Enzymatic Hydrolysis

KANG Guang-bo,YUAN Xing-zhong,ZENG Guang-ming,LIU Jia(College of Environmental Science and Engineering,Hunan University,Changsha 410082,China)  
The effect of combination pretreatment with ultrasound and acid to the chemical composition of rice straw and its enzymatic hy-drolysis were investigated.Meanwhile it was compared with the acid-alone pretreated process.The results showed that in contrast to the un-pretreated rice straw,both the content of hemicelluloses and lignin in the pretreated rice straw decreased at a maximum of 64.46% and 62.19% with the ultrasound-assisted acid respectively,and the content of cellulose increased at a maximum of 73.20%,while the rice straw pretreated by acid only were 56.72%(hemicelluloses),59.90%(lignin)and 53.41%(cellulose)respectively.The enzymatic hydrolysis condi-tions of these two pretreatments were optimized by an orthogonal test.Both methods of the optimal enzymatic hydrolysis conditions were the same:pH 4.8,temperature 45 ℃ and enzyme loading 20 mg.g-1 substrate.Finally,it was indicated by the results that rice straw pretreated by ultrasound-assisted had the highest concentration of reducing sugar by 26.4 g.L-1 after an 108 h enzymatic hydrolysis,and the rice straw pretreated by acid only had 26.2 g.L-1 after an 120 h enzymatic hydrolysis.The rice straw was pretreated by ultrasound-assisted had a higher hydrolysis rate and produced a hydrolysate with higher glucose content and lower xylose content which was more suitable for subsequent fer-mentation in comparison with the one by acid alone.
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