Rice straw contains more ash (mainly in the form of silica) in comparison to other lignocellulosic materials. Silica has several major roles in the rice plant such as enhancement of grain yield, phenolic and carbohydrate synthesis, and plant cell wall protection (Van Soest, 2006). In addition, the presence of silica in outer layer of rice straw protects other components in the inside layer (Lynam et al., 2012). Therefore, unlike wheat straw, rice straw is not suitable for animal feed and its bioprocessing is more complex.