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.