Sunday, May 4, 2008
3-51

Optimization of an aqueous ammonia-soaking process for the enhanced enzymatic hydrolysis of rice straw by cellulase

Ja Kyong Ko1, Jin Seop Bak1, and Kyoung Heon Kim2. (1) Division of Food Bioscience and Technology, Korea University, College of Life Sciences and Biotechnology, Anam-dong, Seongbuk-gu, Seoul, South Korea, (2) School of Life Science & Biotechnology, Korea University, College of Life Sciences and Biotechnology, Anam-dong, Seongbuk-gu, Seoul, South Korea

Rice straw, which is the major lignocellulosic biomass in South Korea, was pretreated by using aqueous ammonia at moderate temperatures for the enhancement of enzymatic hydrolysis to achieve maximum amount of fermentable sugar.  In this study, the effects of various operating variables including temperature, time, concentration of ammonia, and solid-to-liquid ratio (S/L ratio) on the degree of delignification and the enzymatic digestibility were investigated and optimized by using a response surface methodology (RSM).  The ranges of the batch reaction conditions tested were a temperature of 50-70°C, a reaction time of 4-12 h, and an ammonia concentration of 12-28 wt% at a fixed S/L ratio in 1:6.  In the present study, the digestibility of the aqueous ammonia-pretreated rice straw by commercial cellulase was significantly increased in comparison with the control which was not pretreated with ammonia.  The experimental and RSM results showed that the effects of reaction time and temperature were significant on the degree of lignin removal and enzymatic digestibility of the rice straw.  The ammonia concentrations in the range tested in this study had little impact on the delignification and enzymatic digestibility of the rice straw.  The optimum reaction conditions for achieving the maximum delignification and enzyme digestibility, which were determined to be out of experimental range by the canonical analysis, was further found by using the ridge analysis.


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