Enhanced biomethane generation from the anaerobic digestion of wilted corn straw via control in mesophilic and thermophilic temperature intervals

Abstract

Anaerobic digestion (AD) at mesophilic and thermophilic interval temperatures has received increasing attention due to an unexpectedly higher methane yield. However, there is no general consensus and the mechanisms of microbial regulation under interval temperature remain unclear. Therefore, this study evaluated the effect of conventional and interval temperatures on methanogenesis performance and microbial regulation in continuous AD of wilted corn straw. The results demonstrated that the hydrolysis rate increased with increasing temperatures, probably due to the predominant Firmicutes and Proteobacteria, whose abundance in D55 was more than 72% and 19%, respectively. However, in the stable period (31–55 d) experiments, digesters D35, D45, and D55 achieved an average methane yield of 224 ± 34, 311 ± 55, and 261 ± 49 N mL/g VS/d, respectively. Interval temperature substantially enhanced methane yield by 39.4% and 19.0% compared to that from mesophilic and thermophilic digesters, respectively. A higher proportion of Methanosarcina (94.42–94.73%) promoted the acetoclastic methanogenesis at interval temperature, implying that methanogenesis, rather than hydrolysis, is limited at the thermophilic temperatures because of the loss of Methanosarcina. Furthermore, a high abundance of essential genes involved in methane metabolism was found to stimulate methane production in the interval temperature digester. These findings revealed that the interval temperatures may be a balanced zone between hydrolysis and methanogenesis for achieving higher methane yield and provided a new perspective strategy for AD.