A technology for strongly improving methane production from rice straw: freeze–thaw pretreatment

Overcoming the complex three dimensional structure of biomass is a major challenge in enhancing anaerobic digestion (AD) efficacy. Freeze–thaw pretreatment was proposed herein in order to improve methane production from rice straw. The effect was notable: average methane content for group-A (−4 °C) and -B (−20 °C) were A1 (−4 °C, 12 h): 40.0%, A2 (−4 °C, 24 h): 40.5%, A3 (−4 °C, 48 h): 42.2%; B1 (−20 °C, 12 h): 44.2%, B2 (−20 °C, 24 h): 45.7%, B3 (−20 °C, 48 h): 46.0%, the increases were 88.8–99.1% and 108.8–117.2%, respectively, compared with control (CK) (21.2%). Total methane production for group-A and -B were A1: 22.8 mL g(−1) TS, A2: 24.7 mL g(−1) TS, A3: 27.8 mL g(−1) TS; B1: 29.9 mL g(−1) TS, B2: 31.3 mL g(−1) TS, B3: 32.0 mL g(−1) TS, compared with CK (7.6 mL g(−1) TS), the increases were 200.0–265.8%, 293.4–321.1%, respectively. The technical digestion time (T(80)) was shortened by 8 days. Therefore, the maximum methane production was obtained under conditions of −20 °C and 48 h. This study proposed an efficient pretreatment method that broadens the horizon of improving biomass conversion into bioenergy.