Effect of steam explosion pretreatment on the anaerobic digestion of rice straw

Abstract

Rice straw pretreated under various conditions of temperature, ranging from 200 to 220 °C, and time, from 60 to 240 s, was used as the substrate in an anaerobic biogas recovery process. Steam explosion-pretreated rice straw displayed a significant improvement in physicochemical properties compared to untreated rice straw. The biogas production rate increased in all pretreated rice straw systems with shortened start-up periods, and the highest biogas production rate reached 328.7 mL g⁻¹ TS (total solid content) under steam explosion pretreatment conditions of 200 °C/120 s, corresponding to a 51% increase. In addition, upon pretreatment at 200 °C/120 s, the degradation rates of cellulose and hemicellulose in the system reached 53.46% and 49.54%, which were 13.72% and 16.79% higher than in the control, respectively. PCR-DGGE analysis showed that the distributions of specific species of bacteria and archaea varied among different samples. There were clear differences in the bacterial population between pretreated and untreated groups during the set-up period and early stage. During the mid and final stages, pretreated systems had more diverse communities in the digester than the untreated system. Steam explosion pretreatment of the rice straw also led to the earlier presence of cellulolytic bacteria. Furthermore, the species of cellulolytic bacteria in pretreated systems were Clostridium sp. while those in the untreated reactor were Pseudomonas sp. The succession of archaea in the microbial community at different stages in the pretreated and untreated systems was not as obvious as that of bacteria. The results indicate that the physicochemical properties of rice straw were altered by the steam explosion pretreatment, which led to more efficient biogas production due to changes in the bacterial and archaeal species in the pretreated system.