Biomass Particle Size Influences Sugar Conversion

The lignocellulosic biomass (LCB) from crop residues contains about 65-75% of cellulose and hemicellulose that could be converted into fermentable sugars, a renewable source for producing biofuel. It is widely believed that when we reduce the particle size, the surface area increases which results in higher digestibility.  We designed experiments to test the effect of particle size (2mm, 5mm, 2cm and 5cm) on rice straw conversion. We pretreated rice straw using two different AFEX™ pretreatment conditions C1 (100°C; 2:1 ammonia to biomass ratio; 80% moisture and 30 minutes residence time) and C2 (140°C; 1:1 ammonia to biomass ratio; 130% moisture and 50 minutes residence time). Subsequently, we hydrolysed the pretreated biomass at different glucan loading (1%, 3% and 6%) using commercial enzymes (Spezyme CP and Novozyme 188) and determined the sugar yield. AFEX™ C2 conditions made the treated rice straw substrate more susceptible to enzymatic hydrolysis than AFEX™ C1 conditions. Interestingly, the largest particle size of rice straw (5 cm) was found to be more digestible when compared to smaller particle sizes (2mm, 5mm and 2cm) under the given enzyme hydrolysis conditions. Viscosity measurements and imaging has been done to explain the phenomenon. To the best of our knowledge, this is the first time such a trend has been observed.