Effect of pretreatment solutions and conditions on decomposition and anaerobic digestion of lignocellulosic biomass in rice straw

This study assessed the effects of hot water, acid, and alkali pretreatments on the lignocellulosic composition of rice straw and methane production potential of the pretreated solids-reagent mixture. Autoclaving (121 °C, 1.45 atm, 60 min) after addition of 2% H2SO4 showed the highest lignocellulose decomposition efficiency of 65.4%. However, the methane production potential was even smaller than that of the untreated sample, indicating the inhibitory effect of the acid in the biogas production process. On the other hand, hot water- and alkali-pretreated samples showed a factor of 2.1 greater methane production potential than untreated sample despite the relatively lower lignocellulose decomposition efficiency of 17.0–50.4%. By simply keeping the rice straw immersed in water at 100 °C for 30–60 min. or autoclaving prior to anaerobic digestion, the methane production potential of 805.8–824.2 mL of CH4/g total carbon and the overall lignocellulose degradability of 73.6–84.4% was achieved. The results of this study show the potential of hot water pretreatment as an efficient, chemical-free method to improve the feasibility of methane production from rice straw.